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Loss rates of acetone in filtered and unfiltered coastal seawater
Marine Chemistry 150 (2013) 39–44
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Loss rates of acetone in filtered and unfiltered coastal seawater Warren J. de Bruyn, Catherine D. Clark ⁎, Lauren Pagel, Harpreet Singh School of Earth and Environmental Sciences, Schmid College of Science and Technology, Chapman University, One University Drive, Orange, CA 92866, USA
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Article history: Received 9 July 2012 Received in revised form 19 December 2012 Accepted 18 January 2013 Available online 4 February 2013 Keywords: Acetone loss Coastal waters Particle-mediated rate
a b s t r a c t Loss rates of acetone were measured in filtered and unfiltered seawater samples over a 12 month time period at a Pacific Ocean coastal site in Orange County, Southern California, USA, using purge and trap isotope-dilution gas chromatography–mass spectrometry (GC/MS). The average measured first-order rate constant for acetone loss in unfiltered seawater (biotic and abiotic rate) was 0.12± 0.05 h−1 corresponding to a half-life of 5.8± 2.4 h. The observed loss rate in filtered seawater (abiotic rate) was less than 10% of this. Seasonal variations were observed, with higher loss measured in winter and after rain events. Diurnal effects were also observed, with loss rates higher earlier in the day and lower at noon. These are attributed to seasonal and temporal variations in bacteria concentrations, suggesting that bacterial metabolism may be the primary loss process for acetone in urbanized coastal waters. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Oxygenated hydrocarbons are organic compounds ubiquitous in the atmosphere at concentrations ranging from low parts per trillion (ppt; acetaldehyde) to low parts per billion (ppb; methanol) (Singh et al., 2001, 2004). They are more abundant than non-methane hydrocarbons and react rapidly with hydroxyl radicals (OH) (Singh et al., 2001, 2004). These species produce hydroxyl and hydroperoxy radicals (HOx), ozone (O3), carbon monoxide (CO), peroxyacetyl nitrate (PAN) and formaldehyde (CH2O) and can contribute to particle formation in the atmosphere (Singh et al., 2004; de Gouw et al., 2005; Dufour et al., 2007; Millet et al., 2008, 2010 and references therein). Oxygenated hydrocarbons have a direct impact on the oxidative capacity of the atmosphere by acting as a sink for OH and a source of atmospheric HOx and O3. Over the last decade there have been a number of attempts to inventory sources and analyze budgets but significant uncertainties remain (Marandino et al., 2005; Schade and Goldstein, 2006; Millet et al., 2008, 2010; Naik et al., 2010). The role of the oceans in cycling these species into or out of the troposphere is consistently one of the larger sources of uncertainty or discrepancy in global models (Millet et al., 2008, 2010; Naik et al., 2010). This uncertainty is driven by the relatively limited oceanic measurement database (Williams et al., 2004; Beale et al., 2010; Kameyama et al., 2010; Dixon et al., 2011a,b) and our incomplete understanding of the processes that control the concentrations of these species in seawater. Acetone is one of the oxygenated hydrocarbons that plays a major role in the production of HOx in the upper troposphere. Although
⁎ Corresponding author. Tel.: +1 714 628 7341. E-mail address: [email protected] (C.D. Clark). 0304-4203/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.marchem.2013.01.003
ozone photolysis is the major source of OH in much of the troposphere (Finlayson-Pitts and Pitts, 1999), the direct photolysis of acetone has been estimated to be responsible for approximately 18% of the total HOx budget in the drier upper troposphere (Arnold et al., 2004). Sources of acetone to the atmosphere include anthropogenic emissions, biomass burning, terrestrial vegetation and plant decay, and the gas-phase oxidation of organic species (Singh et al., 1994; Brasseur et al., 1998; Wang et al., 1998; Collins et al., 1999; Singh et al., 2000). The oceans are believed to be important but at present it is not clear whether they are a net sink or source based on contradictory experimental data. For example, a large oceanic source was inferred from aircraft measurements over the remote Pacific Ocean (Singh et al., 2001). An analysis of the global budget based on these data suggested that the oceanic source comprised as much as 28% of the estimated total global sources of 95 Tg·yr−1 and was a net source of ~13 Tg·yr−1 (Jacob et al., 2002). However, eddy correlation direct flux measurements over the Pacific Ocean indicated that the flux of acetone is into, rather than out of, the ocean for most of the tropical and northern Pacific Ocean (Marandino et al., 2005); analysis of these data suggested that the oceans are a net sink for acetone of ~30 Tg·yr−1. A more recent budget calculation based on observations during the CARABIC field campaign also suggested that the oceans are a net sink, but on a smaller scale of ~8 Tg·yr−1 (Elias et al., 2011). There are a number of potential sources and sinks for acetone in seawater. Several studies have shown that acetone and other oxygenated hydrocarbons are produced photochemically in surface ocean waters irradiated by sunlight (Mopper and Stahovec, 1986; Kieber and Mopper, 1987; Kieber et al., 1990; Kieber and Mopper, 1990; Zhou and Mopper, 1997; de Bruyn et al., 2011). Biological production of acetone has been demonstrated in laboratory cultures (Weyer and Rettger, 1927; Nemecek-Marshall et al., 1995) and modeling studies suggest that biology could be an important source for some oxygenated hydrocarbons in the open ocean (Millet et al., 2008). However,
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laboratory experiments indicate that photoproduction is the dominant production process for acetone (de Bruyn et al., 2011). Acetone loss in seawater is less well characterized than production. While the fate of larger hydrocarbons, particularly aromatics like benzene and toluene, have been studied in some detail in seawater, little is known about the smaller oxygenated hydrocarbons like acetone (Wakeham et al., 1983). Loss has been demonstrated in cultures (Rathbun et al., 1982), and Dixon et al. (2011a,b) recently found that methanol is rapidly oxidized biologically in the tropical and northeast Atlantic Oceans. For acetone, earlier laboratory studies showed microbial uptake of acetone in bacterial cultures (Sluis and Ensign, 1997; Rathbun et al., 1982) and an insignificant loss due to direct photolysis in fresh and riverine waters (Rathbun et al., 1982). However, to the best of our knowledge, no direct measurements of acetone loss rates have been made in seawater. In this paper, we have measured the loss of acetone in filtered and unfiltered seawater from a Pacific Ocean coastal site in Southern California to probe biotic and abiotic loss processes. Seasonal and temporal variabilities are discussed and results are compared to the literature where possible. 2. Methods 2.1. Site and sample preparation Water samples (1 L) were collected in glass bottles between November 2009 and November 2010 in the Santa Anna River Mouth (SAR) at Huntington State Beach (HSB) in Orange County, California, USA (33°37′32″ N; 117°57′01″ W) and immediately transported back to the laboratory for filtering within 1 h. Four additional samples were collected from Newport Beach Pier (NBP; 33 36.389 N 117 55.830 W) 3 km down coast from HSB for comparison. Samples were generally collected in the morning because of logistics, but some were collected later in the day to test for changes due to sampling time. The temperature and salinity were measured in situ with a standard laboratory Traceable® Thermometer and a YSI CTD respectively. In the laboratory, samples were split into two 500 mL aliquots, one of which was filtered to remove particles, plankton and bacteria through 0.2 μm filters (Millipore, nitrocellulose). Some samples were filtered through 0.8 μm filters (Millipore) for comparison purpose. 2.2. Acetone loss measurements Both filtered and unfiltered seawater samples were spiked with fully deuterated (d-6) acetone (4 to 126 nM; Aldrich) and incubated in a water bath, in 150 mL glass syringes with no head space, and wrapped in aluminum foil to block light. Most incubations were carried out at the temperature of the seawater measured at the time of sampling (typically around 17 °C) or at laboratory temperature (consistently within 5 °C of seawater temperature). Experiments were also carried out to test the effects of incubation across a wider temperature range (10–30 °C). For analyses of acetone concentration, 5–10 mL samples were removed periodically and analyzed by purge and trap isotope-dilution GC/MS. Unfiltered samples (for biotic processes) were analyzed immediately within 1 h of collection and filtered samples (for abiotic processes) were stored in a refrigerator and analyzed within 24 h. Acetone loss rates were determined from the observed rate of change of d-6 acetone. The rate for the filtered sample represents the abiotic or chemical loss rate (in the absence of most particles and biology). Particle and bacteria mediated loss rates can then be determined from the difference between the loss rates measured for the filtered and unfiltered samples. We use isotopically labeled acetone to decouple production and loss processes. If we were looking at natural acetone, changes would reflect both production and destruction processes. Therefore, if we saw decay in natural acetone, it would be a net decay rate. Since isotopically labeled acetone is not produced in seawater, when we
look at changes in a spike we are looking at loss only i.e. an absolute loss rate. We also use the isotope to avoid laboratory contamination and the effects of cell rupture while filtering. We expect natural acetone to be consumed at the same first order decay rate measured for the isotope, assuming minimal isotopic kinetic effects. We have some limited data that suggests that kinetic isotope effects are minimal. While monitoring the decay of a d-6 spike we also monitored the decay of natural acetone however, uncertainties for the natural acetone are much higher due to among other things a variable blank associated with contamination from laboratory air. For a small subset of loss experiments (n = 7) in which precision was comparable to the d-6 measurements the natural acetone decay rate was 20% higher than the isotopically labeled acetone decay rate. 2.3. Analytical methodology Acetone concentrations were measured by isotope-dilution purge and trap GC/MS. In isotope-dilution analysis, a species with two or more naturally occurring stable isotopes is analyzed in the presence of a standard in which one of the naturally occurring isotopes has been enriched. The concentration of the analyte is then determined from the measured isotope ratio. C-13 labeled acetone was used as the internal standard. The purge and trap system is a modified version of an instrument used for methyl bromide and alkyl nitrate analysis (Tokarczyk et al., 2003; Dahl et al., 2003). Seawater is injected into a calibrated volume and transferred under He pressure to a glass-fritted sparger. Sample injection volume for analysis was 0.6 mL for samples from 11/20/09 to 3/22/10 and increased to 4.2 mL for the remaining samples to test the robustness of the technique. Helium is sparged (100–150 mL·min−1) through the sample and the dissolved gases in He flow through a cold trap (−30 °C) to a glass bead cryotrap immersed in liquid nitrogen; the cold trap minimizes water reaching the liquid nitrogen trap. The trapped gases are thermally desorbed and transferred in He to the GC (Shimadzu, 14A) with a Poroplot Q column and into a quadruple mass spectrometer (HP 5973). A gas loop of a 1 ppm C-13 labeled internal acetone standard (Apel-Riemer Environmental Inc., Denver, Colorado) is added to the base of the sparger, and concentrations are calculated from the ratio of the unlabeled and labeled acetone peaks at m/e 58 and 61 respectively. In this experiment where we are following the loss of d-6 acetone, concentrations are determined from the ratio of d-6 acetone and c-13 labeled acetone at m/e 64 and 61 respectively. Standard volumes injected varied between 250 and 800 μL. This system has a detection limit of approximately 0.1 nM acetone for a 5 cm3 water sample. The measured precision during these experiments was ~2.5% across the range of spike concentrations used. 3. Results A total of 25 coastal water samples were collected over a 12 month period from November 2009 to November 2010 (Table 1). Salinities at the Santa Anna River Mouth averaged 26± 2 over this period, typical of this tidally-flushed estuarine environment that doesn't receive regular large fresh water inputs in the absence of rain events (Boehm et al., 2002). Temperatures at the time of sample collection were relatively consistent over the study time-frame, averaging 18± 1 °C. Decreases in salinity were observed in a few instances after isolated rain events and were generally associated with small temperature increases. Typical isotopically-labeled d-6 acetone concentrations as a function of time are shown in Fig. 1 for a 0.2 μm filtered and unfiltered water sample. Unfiltered samples will include loss from both abiotic reactions in the water and particulate phases and biological processing from bacteria in free-living and particle associated reactions, whereas degradation in filtered samples should primarily be due to abiotic, non-particle-mediated processes i.e. chemical reactions in solution. Initial spiked d-6 acetone concentrations were varied from 3 to 126 nM with an average of 59 ± 39 nM to cover the range of ambient
W.J. de Bruyn et al. / Marine Chemistry 150 (2013) 39–44 Table 1 Sampling dates and times, measured salinity (sal. in ppt), ambient temperature (Tw), initial spiked isotopically labeled acetone concentrations ([Ac], nM), and 1st order loss rate constants (k1). Date 11/20/09 12/11 1/06/10 1/11 1/13 1/19 3/10 3/15 3/22 4/05 4/12 4/19 4/21 4/26 5/03 5/05 5/10 5/12 8/03a 8/05a 8/09a 8/12a 10/10 10/21 11/02
Local time 14:00 18:00 7:50 7:55 7:55 7:55 6:45 6:50 6:50 6:40 6:50 6:40 6:40 6:50 6:40 6:50 6:50 6:55 8:07 7:11 6:48 8:07 10:15 10:15 8:50
Sal. 28.3 26.5 25.1 27.4 27.6 24.9 22.5 25.7 22.8 27.9 25.2 26.4 24.9 27.8 20.5 26.6 27.7 26.2 b b b b b b b
Tw (°C) c
18.8 17.9c 14.9c 16.4c 16.8c 15.9c 18.9c 17.0c 17.9c 16.3 16.3 18.0 17.5 16.5 19.0 18.8 17.5 18.9 16.8 17.7 18.1 15.3 18.9 18.9 18.1
[Ac] (nM)
k1 (hr−1)
89 102 62 98 91 126 42 63 53 21 4.9 4.4 53 27 5.2 16 3.2 31 72 51 118 45 15 28.7 263
0.09 ± 0.01 0.10 ± 0.02 0.13 ± 0.02 0.10 ± 0.01 0.12 ± 0.03 0.18 ± 0.02 0.09 ± 0.02 0.16 ± .02 0.15 ± 0.05 0.22 ± 0.02 0.17 ± 0.02 0.12 ± 0.01 0.15 ± 0.02 0.16 ± 0.01 0.20 ± 0.02 0.16 ± 0.03 0.15 ± 0.02 0.13 ± 0.04 0.084 ± 0.02 0.039 ± 0.025 0.033 ± 0.028 0.017 ± 0.005 0.047 ± 0.007 0.064 ± 0.008 0.060 ± 0.014
a
Water samples from NBP. No measurement made. c Samples incubated at room T (18–20 °C); remainder incubated at ambient water T measured at time of sampling. b
acetone concentrations found in a prior study in these waters (De Bruyn et al., 2012) and to probe the concentration dependence of the acetone loss kinetics. The solid lines in Fig. 1 are linear fits to the data shown for ease of viewing. First-order (exponential decay) rate constants were obtained from the slope of a plot of ln [acetone]0 / [acetone]t vs. time with an average R 2 value of 0.854; rate constants are given in Table 1. For the unfiltered samples, where both chemical and biotic and abiotic particle mediated loss processes occur, the average first-order rate constant was 0.12 ± 0.05 h −1. Errors are standard deviations of the slope of linear least squares fits to the first order loss data. Based on the average first-order rate constant, the corresponding half-life is 5.8 ± 2.4 h, where the half-life is given by ln 2/k for a first order process.
Fig. 1. Concentration of isotopically-labeled d-6 acetone ([Ac], in nM) as a function of time elapsed (in hr) for a typical split filtered (○) and unfiltered (●) seawater sample. Data shown for sample from 04/05/2010. Lines shown from linear regression fit to the data (filtered R2 = 0.291, p = 0.575; unfiltered R2 = 0.988, p = 0.0002).
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Changes in d-6 concentrations for the 0.2 μm filtered samples were minor relative to the changes described above for the unfiltered samples. Changes in acetone levels for filtered samples (i.e. abiotic rate only) were typically less than 10% of the observed changes for unfiltered samples, with an estimated average first-order rate constant of 0.005 ± 0.002 h −1 (standard error, n = 8) with a corresponding half-life of 139 ± 56 h. When samples were filtered through 0.8 μm filters instead of 0.2 μm, the unfiltered and filtered samples had similar loss rates within the uncertainties of the measurements suggesting that the species responsible for the loss are in the size range between 0.2 and 0.8 μm. In seawater, this size fraction includes both inorganic particles and bacteria, whereas zooplankton and dinoflagellates are in much larger size modes > 40 μm (Ahn and Grant, 2007). To confirm first-order kinetics, loss rates (changes in concentration as a function of time) were measured as a function of the initial spiked d-6 acetone concentration (Fig. 2). This was done for all samples collected in the morning at approximately the same time during the winter months at the Santa Anna River Mouth (16 out of 25 samples) to minimize seasonal and temporal variabilities. The observed positive linear relationship suggests that the kinetics is in fact first or pseudo first order. For the same subset of data, a plot (not shown) of first-order loss rate constants as a function of incubation temperature showed that temperature had minimal impact on the observed loss rate over the temperature range studied (10–30 °C; slope= −0.0021; int= 0.1996; R2 = 0.2505). Observed differences between average 10 °C data and 30 °C data were not significant at the 95% confidence limit (Student's t-test). Similarly, salinity had little impact on measured loss rates. A slight decrease in the observed first-order rate constant was observed as salinity increased from 20 to 28. A linear fit to the data had a slope of −0.0038, an intercept of 0.2401 and R2 = 0.0481; this was not a significant relationship over the salinity range observed in these coastal waters based on a p-test (p= 0.05). However, extrapolation to a salinity of 36 for seawater would give loss rates that are 36% lower. The slight decrease observed here is likely not directly due to salinity differences but rather to variability in particle concentrations or bacteria density and populations that co-vary with the same factors that impact salinity (e.g. rain events, tidal changes, etc.). 4. Discussion The acetone loss associated with small particles removed by filtration through 0.2 μm filters could be due to physical or biological processes, specifically physical adsorption to small particles or metabolism by
Fig. 2. Rates (nM·hr−1) as a function of the initial concentration of d-6 acetone (nM) added to the sample for all early morning samples. Line shown from linear regression fit to the data with slope = 0.0998 ± 0.0067 and intercept = 0.01 ± 0.37 (R2 = 0.971; p b 0.0001).
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bacteria. Suspended particle size distributions in these waters have been measured on seasonal and shorter time scales by light scattering and optical microscopy (Ahn et al., 2005; Ahn and Grant, 2007). Three types of particles have been identified; large plant and zooplankton debris (>200 μm); dinoflagellate particles (~40 μm); and inorganic particles b5 μm (Ahn and Grant, 2007). Increases in the fine particle mode (b5 μm) were typically associated with rainfall events, increased river discharges and increased fecal indicator bacteria (FIB) concentrations. Natural bacterial populations in marine coastal waters consist of both single-cell and colony forming bacterioplankton and are of diverse phylogenic origin, including subdivisions of the proteobacteria class and cytophaga-flexibacter-bacteroides phylum (Pinhassi et al., 1997; Pinhassi and Hagstrom, 2000). In addition, coastal waters adjacent to highly urbanized regions like Southern California receive inputs of FIB through runoff (Boehm et al., 2002). There have been no studies of natural marine bacterial populations at this beach, but many microbial water quality studies measuring FIB levels have been carried out in the surf zone waters at this site (for example Ahn et al., 2005 and references therein). The Orange County Sanitation District (OCSD) has a long-term monitoring program at this site which includes daily measurements of total coliform, fecal coliform and Enterococci. Variability in FIB in surf zone waters on both short and long time scales has been well documented (Boehm et al., 2002; Boehm, 2007). In general, bacteria levels are highest over the winter months (December through February) when rainfall levels are highest, and show decreases in summer and with locations farther from river outlets like the SAR (Boehm et al., 2002; OCSD). In Fig. 3, we show our measured first order particle-mediated loss rate constants as a function of time of year at HSB. All August 2010 data are for water samples from Newport Beach Pier taken for an ancillary study; however, in the summer dry season we expect these adjacent sites to be comparable to those of HSB because of the lack of high-volume riverine inputs and the long-shore currents that ensure rapid mixing of any low-volume runoff and wetland discharges (Grant et al., 2005). Also shown in Fig. 3 are discharge rates for the SAR (USGS; http://wdr.water.usgs.gov/wy2009/pdfs/ 11078000.2009.pdf; accessed 06/27/2012) over the same time period. Note that these are shown on a log scale for clarity of viewing, so stream flows in the winter wet season are 3 to 4 orders of magnitude higher than in the summer dry season. The observed seasonal cycling in river discharge rate is typical with what has been observed in prior studies (Boehm et al., 2002; OCSD). Increases in SAR flows are associated with the rain events that occurred in the wet season (from December through March). Southern California has a semi-arid
Fig. 3. First order loss rate constants (k1 in hr−1; ■) as a function of time of year. Superimposed on the data are river discharge stream gauge data every 5 days for the Santa Anna River from the United States Geological Survey (—; in ft3 s−1). Note that these are shown on a log scale for clarity of viewing so stream flows in the winter wet season are 3 to 4 orders of magnitude higher than in the summer dry season.
Mediterranean type climate with low annual rainfalls and sporadic rain events. Total monthly rainfall for the study period ranged from a high of 3.69″ in December 2009 to lows of 0″ from July through September 2010 (http://www.cnrfc.noaa.gov/monthly_precip_2010.php; accessed 6/27/2012). Monthly rainfall for the summer dry season from May through September 2010 averaged 0.002″ and was over 3 orders of magnitude higher at 2.5″ for the winter wet season from December 2009 through February 2010. While the acetone loss dataset does not cover the dry season extensively, rates are higher in the winter months during the rainy season when river water discharges are higher. Over the wet season, k1 averages 0.14 ± 0.04 h −1 whereas it is statistically significantly lower at 0.05 ± 0.02 h −1 over the dry season. These seasonal changes could be due to increases in loss efficiencies through increases in bacterial levels associated with runoff or to increased concentrations of small particles associated with increased river discharge (Ahn and Grant, 2007). FIB levels typically increase with a rain event and take a few weeks to return to baseline levels (Boehm et al., 2002). In addition to the FIB, there will also be marine bacteria in the water which should show similar seasonal variability. Increases and changes in marine bacterial populations might also be expected after rain events due to an influx of nutrients. Significant changes in the abundance of different marine bacteria over the year have been observed in coastal marine environments (Pinhassi et al., 1997) with distinct communities and lower levels of production observed in summer vs. fall and winter seasons. Another factor affecting natural bacterial populations is the near-shore coastal upwelling that typically occurs along the coast of Southern California from March through September, bringing in colder, nutrient rich waters from depth. This results in phytoplankton blooms which can be observed through satellite imaging. Different marine bacterial species have been observed to dominate during spring when phytoplankton blooms occur (Pinhassi et al., 1997). Upwelling events would explain the increases in loss rate constants in Spring and Summer 2010 that were not associated with significant increases in FIB levels and stream gauge flows due to large rainfall events. Any upwelling events would be indicated by a decrease in water temperatures. For example, k1 was 0.0839 h −1 on 8/4/2012 when water temperatures were 16.8 °C and 60% lower at 0.033 h −1 on 8/9/2012 when the water temperature was 18.1 °C. Similar effects were seen in early April when water temperatures dropped to 16.3 °C in association with an increase in k1 by 25% over typical levels for that time of year. Although we have limited samples taken at later times during the day, there appears to be a diurnal effect on the observed first order loss rate constants (Fig. 4), with higher values obtained during the early morning hours than the afternoon and evening. The early morning values for k1 average 0.14± 0.02 h−1 vs. the statistically lower average for the late morning and afternoon hours of 0.077 ± 0.02 h−1. These diurnal effects suggest that the observed decay is most likely due to consumption by bacteria rather than adsorption onto inorganic particles, since bacteria are affected by changing sunlight levels whereas inorganic particles should not be. It has been well-established at this beach that FIB undergo diurnal cycling; highest bacterial levels occur in the early morning, decrease to a minimum after solar noon and rebound at night (Boehm et al., 2002). These patterns have been attributed to bacterial mortality and oxidative stress associated with ultraviolet light and photochemically produced oxidants like hydrogen peroxide acting as sinks that vary with time of day (Boehm et al., 2002; Boehm, 2007), coupled with reseeding at night from the beach sediments and local wetland outflows as sources (Grant et al., 2001; Ahn et al., 2005; Yamahara et al., 2007). Few data have been published on the loss of acetone in seawater. Rathbun et al. (1982) measured acetone consumption by cultured sewage bacteria in an Oceanography International E/BOD respirator. They report a first order decay rate of 0.163 ± 0.102 h−1 in experiments
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Acknowledgments The authors thank the National Science Foundation (OCE # 0727614) for funding this work. References
Fig. 4. Diurnal variability in first-order loss rate constants (■; hr−1) as a function of local time. Also shown on the plot are solar irradiation levels (straight line; W m−2) at the same site reproduced from data in Clark et al. (2009).
in which the culture was not pretreated with acetone, and a rate of 0.058 ± 0.046 h−1 when the sample was pretreated. Initial concentrations in their study were 0.27 to 2.7 mM. They suggest that the rates in the real world would be lower because of the idealized conditions of the experiment. While we can't conclusively state that our observed loss rate is due solely to bacteria and not also inorganic particles, the average first order rate constant of 0.12± 0.05 h−1 we measured here for natural seawater compares well with their measurements in bacterial cultures. Biological loss rates for methanol, another oxygenated hydrocarbon, recently measured in the open ocean are lower than the rates obtained for acetone. Dixon et al. (2011a) report biological oxidation rates for methanol of 2.1 to 8.4 nM·day −1 in surface waters of the northeast Atlantic with surface concentrations of 70–97 nM and 2–146 nM·day −1 in the tropical Atlantic with surface concentrations of 300 nM. Based on their data, we estimate the associated approximate first order rate constants to be 0.001–0.004 h −1 for the northeast Atlantic and 0.0003–0.02 h −1 for the tropical Atlantic. These are 2 to 3 orders of magnitude lower than what we measured in this study for acetone. This difference could partially be attributed to the difference in the environments the measurements were made in, since open ocean waters have significantly lower bacterial population densities and diversity than near-shore waters.
5. Conclusions Acetone can be produced and destroyed in seawater. In theory, removal can occur via a combination of chemical, photochemical and particle-mediated loss pathways (including biological consumption). We measured acetone loss rates in seawater samples from a coastal site in Southern California. Our loss rates for filtered samples (attributed to abiotic, non-particle-mediated rates i.e. chemical processes only) were on the order of 10% or less than the observed loss rates for unfiltered seawater samples (attributed to biotic and abiotic processes like bacterial metabolism and particle sorption). The average first-order loss rate constant measured for unfiltered samples was 0.12±0.05 h−1. Seasonal and temporal trends were observed, with higher loss rate constants measured on average: 1) in the rainy winter wet season vs. the dry summer season; 2) after rain and upwelling events; and 3) earlier in the day. These trends are consistent with established patterns and changes in bacterial levels, suggesting that loss may be due primarily to bacteria rather than non-organic particles.
Ahn, J.H., Grant, S.B., 2007. Size distribution, sources and seasonality of suspended particles in southern California marine bathing waters. Environ. Sci. Technol. 41, 695–702. Ahn, J.H., Grant, S.B., Surbeck, C.Q., Digiacomo, P.M., Nezlin, N.P., Jiang, S., 2005. Coastal water quality impact of stormwater runoff from an urban watershed in southern California. Environ. Sci. Technol. 39, 5940–5953. Arnold, S.R., Chipperfield, M.P., Blitz, M.A., Heard, D.E., Pilling, M.J., 2004. Photodissociation of acetone: atmospheric implications of temperature-dependent quantum yields. Geophys. Res. Lett. 31, LO7110. http://dx.doi.org/10.1029/2003GLO19099. Beale, R., Liss, P.S., Nightingale, P.D., 2010. First oceanic measurements of ethanol and propanol. Geophys. Res. Lett. 37, L24607. http://dx.doi.org/10.1029/2010GL045534. Boehm, A.B., 2007. Enterococci concentrations in diverse coastal environments exhibit extreme variability. Environ. Sci. Technol. 41, 8227–8232. Boehm, A.B., Grant, S.B., Kim, J.H., Mowbray, S.L., McGee, C.D., Clark, C.D., Foley, D.M., Wellman, D.E., 2002. Decadal and shorter period variability of surf zone quality at Huntington Beach, California. Environ. Sci. Technol. 36, 3885. Brasseur, G.P., Hauglustaine, D.A., Walters, S., Rasch, P.J., Muller, J.F., Granier, C., Tie, X., 1998. MOZART, a global chemical transport model for ozone and related chemical tracers: 1. Model description. J. Geophys. Res. 103, 28,265–28,289. Clark, C.D., De Bruyn, W.J., Hirsch, C.M., Jakubowski, S.D., 2009. Hydrogen peroxide measurements in recreational marine bathing waters in Southern California, USA. Water Res. 44, 2203–2210. Collins, W.J., Stevenson, D.S., Johnson, C.E., Derwent, R.G., 1999. Role of convection in determining the budget of odd hydrogen in the upper troposphere. J. Geophys. Res. 104, 26,927–26,941. Dahl, E.E., Saltzman, E.S., De Bruyn, W.J., 2003. A mechanism for the aqueous phase production of alkyl nitrates in seawater. Geophys. Res. Lett. 36, 1271–1275. De Bruyn, W.J., Clark, C.D., Pagel, L., Takahara, C., 2011. Photoproduction of formaldehyde, acetaldehyde and acetone from chromophoric dissolved organic matter in coastal and estuarine waters. J. Photochem. Photobiol. 226, 16–22. De Bruyn, W.J., Clark, C.D., Pagel, L., 2012. Oxygenated Hydrocarbons in Coastal Waters, Book Chapter in Oceanography. In-Tech Open Access Publishing978-953-307-919-6. de Gouw, J.A., Middlebrook, A.M., Warneke, C., Goldan, P.D., Kuster, W.C., Roberts, J.M., Fehsenfeld, F.C., Worsnop, D.R., Canagaratna, M.R., Pszenny, A.A.P., Keene, W.C., Marchewka, M., Bertman, S.B., Bates, T.S., 2005. Budget of organic carbon in a polluted atmosphere: Results from the New England Air Quality Study in 2002. J. Geophys. Res. Atmos. (1984–2012), 110 (D16). Dixon, J.L., Beale, R., Nightingale, P.D., 2011a. Rapid biological oxidation of methanol in the tropical Atlantic: significance as a microbial carbon source. Biogeosci. Discuss. 8, 3899–3921. Dixon, J.L., Beale, R., Nightingale, P.D., 2011b. Microbial methanol uptake in the northeast Atlantic waters. ISME J. 5, 704–716. Dufour, G., Szopa, S., Hauglustaine, D.A., Boone, C.D., Rinsland, C.P., Bernath, P.F., 2007. The influence of biogenic emissions on upper-tropospheric methanol as revealed from space. Atmos. Chem. Phys. 7, 6119–6129. Elias, T., Szopa, S., Zahn, A., Schuck, T., Brenninkmeijer, C., Sprung, D., Slemr, F., 2011. Acetone variability in the upper troposphere: analysis of CARABIC observations and LMDZ-INCA chemistry-climate model simulations. Atmos. Chem. Phys. 11, 8053–8074. Finlayson-Pitts, B.J., Pitts, J.N., 1999. Chemistry of the Upper and Lower Atmosphere: Theory, Experiments, and Applications. Elsevier Science & Technology Books. Grant, S.B., Sanders, B.F., Boehm, A.B., Redman, J.A., Kim, J.H., Mrse, R.D., Chu, A.K., Gouldin, M., McGee, C.D., Gardiner, N.A., Jones, B.H., Svejkovsky, J., Leipzig, G.V., Brown, A., 2001. Generation of Enterococci bacteria in a coastal saltwater marsh and its impact on surf zone water quality. Environ. Sci. Technol. 35, 2407–2416. Grant, S.B., Kim, J.H., Jones, B.H., Jenkins, S.A., Wasyl, J., Cudaback, C., 2005. Surf zone entrainment, along-shore transport and human health implications of pollution from tidal outlets. J. Geophys. Res. 110, C10025. http://dx.doi.org/10.1029/2004JC002401. Jacob, D.J., Field, B.D., Jin, E.M., Bey, I., Li, Q., Logan, J.A., Yantosca, R.M., 2002. Atmospheric budget of acetone. J. Geophys. Res. 107 (D10), 4100. http://dx.doi.org/10.1029/ 2001JD000694. Kameyama, S., Tanimoto, H., Inomata, S., Tsunoga, U., Ooki, A., Takeda, S., Obata, H., Tsuda, A., Uematsu, M., 2010. High-resolution measurement of multiple volatile organic compounds dissolved in seawater using equilibrator inlet–proton transfer reaction-mass spectrometry (EI–PTR-MS). Mar. Chem. 122, 59–73. Kieber, D.J., Mopper, K., 1987. Photochemical formation of glyoxylic and pyruvic acids in seawater. Mar. Chem. 21, 135–149. Kieber, R.J., Mopper, K., 1990. Determination of picomolar concentrations of carbonyl compounds in natural waters, including seawater, by liquid chromatography. Environ. Sci. Technol. 24, 1477–1481. Kieber, R.J., Zhou, X., Mopper, K., 1990. Formation of carbonyl compounds from UVinduced photodegradation of humic substances in natural waters: fate of riverine carbon in the sea. Limnol. Oceanogr. 35, 1503–1515. Marandino, C.A., DeBruyn, W.J., Saltzman, E.S., Miller, S.D., Prather, M.J., 2005. Oceanic uptake and the global atmospheric budget of acetone. Geophys. Res. Lett. 32, L15806. http://dx.doi.org/10.1029/2005GL023285. Millet, D.B., Jacob, D.J., Custer, T.G., de Gouw, J.A., Goldstein, A.H., Karl, T., Singh, H.B., Sive, B.C., Talbot, R.W., Warneke, C., Williams, J., 2008. New constraints on terrestrial and oceanic sources of atmospheric methanol. Atmos. Chem. Phys. 8, 6887–6905.
44
W.J. de Bruyn et al. / Marine Chemistry 150 (2013) 39–44
Millet, D.B., Guenther, A., Siegel, D.A., Nelson, N.B., Singh, H.B., de Gouw, J.A., Warneke, C., Williams, J., Erdekens, G., Sinha, V., Karl, T., Flocke, F., Apel, E., Riemer, D.D., Palmer, P.I., Barkley, M., 2010. Global atmospheric budget of acetaldehyde: 3-D model analysis and constraints from in situ and satellite observations. Atmos. Chem. Phys. 10, 3405–3425. Mopper, K., Stahovec, W.L., 1986. Sources and sinks of low molecular weight organic carbonyl compounds in seawater. Mar. Chem. 19, 305–321. http://dx.doi.org/ 10.1016/0304-4203(86)90052-6. Naik, V., Fiore, A.M., Horowitz, L.W., Singh, H.B., Wiedinmeyer, C., Guenther, A., de Gouw, J.A., Millet, D.B., Goldan, P.D., Kuster, W.C., Goldstein, A., 2010. Observational constraints on the global atmospheric budget of ethanol. Atmos. Chem. Phys. Discuss. 10, 925–945. Nemecek-Marshall, M., Wojciechowski, C., Kuzma, J., Silver, G.M., Fall, R., 1995. Marine vibrio species produce the volatile organic compound acetone. Appl. Environ. Microbiol. 61, 44–47. Pinhassi, J., Zweifel, U.L., Hagstrom, A., 1997. Dominant marine bacteriaplankton species found among colony-forming bacteria. Appl. Environ. Microbiol. 63, 3359–3366. Pinhassi, J., Hagstrom, A., 2000. Seasonal succession in marine bacterioplankton. Aquat. Microb. Ecol. 21, 245–256 [Published june 15]. Rathbun, R.E., Stephens, D.W., Schultz, D.J., Tai, D.Y., 1982. Fate of acetone in water. Chemosphere 11, 1097–1114. Schade, G.W., Goldstein, A.H., 2006. Seasonal measurements of acetone and methanol: abundances and implications for atmospheric budgets. Global Biogeochem. Cycles 20, GB1011. http://dx.doi.org/10.1029/2005GB002566. Singh, H.B., O'Hara, D., Herlth, D., Sachse, W., Blake, D.R., Bradshaw, J.D., Kanakidou, M., Crutzen, P.J., 1994. Acetone in the atmosphere: distribution sources and sinks. J. Geophys. Res. 99, 1805–1819. Singh, H., Chen, Y., Tabazedeh, A., Fukui, Y., Bey, I., Yantosca, R., Jacob, D., Arnold, F., Wohlfrom, K., Atlas, E., Flocke, F., Blake, D., Blake, N., Heikes, B., Snow, J., Talbot, R., Gregory, G., Sachse, G., Vay, S., Kondo, Y., 2000. Distribution and fate of selected oxygenated organic species in the troposphere and lower stratosphere over the Atlantic. J. Geophys. Res. 105, 3795–3806.
Singh, H., Chen, Y., Staudt, A., Jacob, D., Blake, D., Heikes, B., Snow, J., 2001. Evidence from the Pacific troposphere for large global sources of oxygenated organic compounds. Nature 410, 1078–1081. Singh, H.B., Slas, L.J., Chatfield, R.B., Czech, E., Fried, A., Walega, J., Evans, M.J., Field, B.D., Jacob, D.J., Blake, D., Heikes, B., Talbot, R., Sachse, G., Crawford, J.H., Avery, M.A., Sandholm, S., Fuelberg, H., 2004. Analysis of atmospheric distribution sources and sinks of oxygenated volatile organic chemicals based on measurements over the Pacific during TRACE-P. J. Geophys. Res. 109, D15S07. http://dx.doi.org/ 10.1029/2003JD003883. Sluis, M.K., Ensign, S.A., 1997. Purification and characterization of acetone carboxylase from Xanthobacter strain Py2. Proc. Natl. Acad. Sci. 94, 8456–8461. Tokarczyk, R., Goodwin, K., Saltzman, E.S., 2003. Methyl chloride and methyl bromide degradation in the southern ocean. Geophys. Res. Lett. 1808, 30. http://dx.doi.org/ 10.1029/2003GLO17459. Wakeham, S.G., Davis, A.C., Karas, J.L., 1983. Mesocosm experiments to determine the fate and persistence of volatile organic compounds in coastal seawater. Environ. Sci. Technol. 17, 611–617. Wang, Y., Jacob, D.J., Logan, J.A., 1998. Global simulation of tropospheric O 3–NO xhydrocarbon chemistry. J. Geophys. Res. 103, 10,713–10,726. Weyer, E.R., Rettger, L.F., 1927. A comparative study of six different strains of the organism commonly concerned in large-scale production of butyl alcohol and acetone by the biological process. J. Bacteriol. 14 (6), 399–424 (PMCID: PMC374969 ). Williams, J., Holzinger, R., Gros, V., Xu, X., Atlas, E., Wallace, D.W.R., 2004. Measurements of organic species in air and seawater from the tropical Atlantic. Geophys. Res. Lett. 31, L23S06. http://dx.doi.org/10.1029/2004GL020012. Yamahara, K.M., Layton, B.A., Santoro, A.E., Boehm, A.B., 2007. Beach sands along the California Coast are diffuse sources of fecal bacteria to coastal waters. Environ. Sci. Technol. 41, 4515–4521. Zhou, X., Mopper, K., 1997. Photochemical production of low-molecular-weight carbonyl compounds in seawater and surface microlayer and their air-sea exchange. Mar. Chem. 56, 201–213.
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Loss rates of acetone in filtered and unfiltered coastal seawater Warren J. de Bruyn, Catherine D. Clark ⁎, Lauren Pagel, Harpreet Singh School of Earth and Environmental Sciences, Schmid College of Science and Technology, Chapman University, One University Drive, Orange, CA 92866, USA
a r t i c l e
i n f o
Article history: Received 9 July 2012 Received in revised form 19 December 2012 Accepted 18 January 2013 Available online 4 February 2013 Keywords: Acetone loss Coastal waters Particle-mediated rate
a b s t r a c t Loss rates of acetone were measured in filtered and unfiltered seawater samples over a 12 month time period at a Pacific Ocean coastal site in Orange County, Southern California, USA, using purge and trap isotope-dilution gas chromatography–mass spectrometry (GC/MS). The average measured first-order rate constant for acetone loss in unfiltered seawater (biotic and abiotic rate) was 0.12± 0.05 h−1 corresponding to a half-life of 5.8± 2.4 h. The observed loss rate in filtered seawater (abiotic rate) was less than 10% of this. Seasonal variations were observed, with higher loss measured in winter and after rain events. Diurnal effects were also observed, with loss rates higher earlier in the day and lower at noon. These are attributed to seasonal and temporal variations in bacteria concentrations, suggesting that bacterial metabolism may be the primary loss process for acetone in urbanized coastal waters. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Oxygenated hydrocarbons are organic compounds ubiquitous in the atmosphere at concentrations ranging from low parts per trillion (ppt; acetaldehyde) to low parts per billion (ppb; methanol) (Singh et al., 2001, 2004). They are more abundant than non-methane hydrocarbons and react rapidly with hydroxyl radicals (OH) (Singh et al., 2001, 2004). These species produce hydroxyl and hydroperoxy radicals (HOx), ozone (O3), carbon monoxide (CO), peroxyacetyl nitrate (PAN) and formaldehyde (CH2O) and can contribute to particle formation in the atmosphere (Singh et al., 2004; de Gouw et al., 2005; Dufour et al., 2007; Millet et al., 2008, 2010 and references therein). Oxygenated hydrocarbons have a direct impact on the oxidative capacity of the atmosphere by acting as a sink for OH and a source of atmospheric HOx and O3. Over the last decade there have been a number of attempts to inventory sources and analyze budgets but significant uncertainties remain (Marandino et al., 2005; Schade and Goldstein, 2006; Millet et al., 2008, 2010; Naik et al., 2010). The role of the oceans in cycling these species into or out of the troposphere is consistently one of the larger sources of uncertainty or discrepancy in global models (Millet et al., 2008, 2010; Naik et al., 2010). This uncertainty is driven by the relatively limited oceanic measurement database (Williams et al., 2004; Beale et al., 2010; Kameyama et al., 2010; Dixon et al., 2011a,b) and our incomplete understanding of the processes that control the concentrations of these species in seawater. Acetone is one of the oxygenated hydrocarbons that plays a major role in the production of HOx in the upper troposphere. Although
⁎ Corresponding author. Tel.: +1 714 628 7341. E-mail address: [email protected] (C.D. Clark). 0304-4203/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.marchem.2013.01.003
ozone photolysis is the major source of OH in much of the troposphere (Finlayson-Pitts and Pitts, 1999), the direct photolysis of acetone has been estimated to be responsible for approximately 18% of the total HOx budget in the drier upper troposphere (Arnold et al., 2004). Sources of acetone to the atmosphere include anthropogenic emissions, biomass burning, terrestrial vegetation and plant decay, and the gas-phase oxidation of organic species (Singh et al., 1994; Brasseur et al., 1998; Wang et al., 1998; Collins et al., 1999; Singh et al., 2000). The oceans are believed to be important but at present it is not clear whether they are a net sink or source based on contradictory experimental data. For example, a large oceanic source was inferred from aircraft measurements over the remote Pacific Ocean (Singh et al., 2001). An analysis of the global budget based on these data suggested that the oceanic source comprised as much as 28% of the estimated total global sources of 95 Tg·yr−1 and was a net source of ~13 Tg·yr−1 (Jacob et al., 2002). However, eddy correlation direct flux measurements over the Pacific Ocean indicated that the flux of acetone is into, rather than out of, the ocean for most of the tropical and northern Pacific Ocean (Marandino et al., 2005); analysis of these data suggested that the oceans are a net sink for acetone of ~30 Tg·yr−1. A more recent budget calculation based on observations during the CARABIC field campaign also suggested that the oceans are a net sink, but on a smaller scale of ~8 Tg·yr−1 (Elias et al., 2011). There are a number of potential sources and sinks for acetone in seawater. Several studies have shown that acetone and other oxygenated hydrocarbons are produced photochemically in surface ocean waters irradiated by sunlight (Mopper and Stahovec, 1986; Kieber and Mopper, 1987; Kieber et al., 1990; Kieber and Mopper, 1990; Zhou and Mopper, 1997; de Bruyn et al., 2011). Biological production of acetone has been demonstrated in laboratory cultures (Weyer and Rettger, 1927; Nemecek-Marshall et al., 1995) and modeling studies suggest that biology could be an important source for some oxygenated hydrocarbons in the open ocean (Millet et al., 2008). However,
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laboratory experiments indicate that photoproduction is the dominant production process for acetone (de Bruyn et al., 2011). Acetone loss in seawater is less well characterized than production. While the fate of larger hydrocarbons, particularly aromatics like benzene and toluene, have been studied in some detail in seawater, little is known about the smaller oxygenated hydrocarbons like acetone (Wakeham et al., 1983). Loss has been demonstrated in cultures (Rathbun et al., 1982), and Dixon et al. (2011a,b) recently found that methanol is rapidly oxidized biologically in the tropical and northeast Atlantic Oceans. For acetone, earlier laboratory studies showed microbial uptake of acetone in bacterial cultures (Sluis and Ensign, 1997; Rathbun et al., 1982) and an insignificant loss due to direct photolysis in fresh and riverine waters (Rathbun et al., 1982). However, to the best of our knowledge, no direct measurements of acetone loss rates have been made in seawater. In this paper, we have measured the loss of acetone in filtered and unfiltered seawater from a Pacific Ocean coastal site in Southern California to probe biotic and abiotic loss processes. Seasonal and temporal variabilities are discussed and results are compared to the literature where possible. 2. Methods 2.1. Site and sample preparation Water samples (1 L) were collected in glass bottles between November 2009 and November 2010 in the Santa Anna River Mouth (SAR) at Huntington State Beach (HSB) in Orange County, California, USA (33°37′32″ N; 117°57′01″ W) and immediately transported back to the laboratory for filtering within 1 h. Four additional samples were collected from Newport Beach Pier (NBP; 33 36.389 N 117 55.830 W) 3 km down coast from HSB for comparison. Samples were generally collected in the morning because of logistics, but some were collected later in the day to test for changes due to sampling time. The temperature and salinity were measured in situ with a standard laboratory Traceable® Thermometer and a YSI CTD respectively. In the laboratory, samples were split into two 500 mL aliquots, one of which was filtered to remove particles, plankton and bacteria through 0.2 μm filters (Millipore, nitrocellulose). Some samples were filtered through 0.8 μm filters (Millipore) for comparison purpose. 2.2. Acetone loss measurements Both filtered and unfiltered seawater samples were spiked with fully deuterated (d-6) acetone (4 to 126 nM; Aldrich) and incubated in a water bath, in 150 mL glass syringes with no head space, and wrapped in aluminum foil to block light. Most incubations were carried out at the temperature of the seawater measured at the time of sampling (typically around 17 °C) or at laboratory temperature (consistently within 5 °C of seawater temperature). Experiments were also carried out to test the effects of incubation across a wider temperature range (10–30 °C). For analyses of acetone concentration, 5–10 mL samples were removed periodically and analyzed by purge and trap isotope-dilution GC/MS. Unfiltered samples (for biotic processes) were analyzed immediately within 1 h of collection and filtered samples (for abiotic processes) were stored in a refrigerator and analyzed within 24 h. Acetone loss rates were determined from the observed rate of change of d-6 acetone. The rate for the filtered sample represents the abiotic or chemical loss rate (in the absence of most particles and biology). Particle and bacteria mediated loss rates can then be determined from the difference between the loss rates measured for the filtered and unfiltered samples. We use isotopically labeled acetone to decouple production and loss processes. If we were looking at natural acetone, changes would reflect both production and destruction processes. Therefore, if we saw decay in natural acetone, it would be a net decay rate. Since isotopically labeled acetone is not produced in seawater, when we
look at changes in a spike we are looking at loss only i.e. an absolute loss rate. We also use the isotope to avoid laboratory contamination and the effects of cell rupture while filtering. We expect natural acetone to be consumed at the same first order decay rate measured for the isotope, assuming minimal isotopic kinetic effects. We have some limited data that suggests that kinetic isotope effects are minimal. While monitoring the decay of a d-6 spike we also monitored the decay of natural acetone however, uncertainties for the natural acetone are much higher due to among other things a variable blank associated with contamination from laboratory air. For a small subset of loss experiments (n = 7) in which precision was comparable to the d-6 measurements the natural acetone decay rate was 20% higher than the isotopically labeled acetone decay rate. 2.3. Analytical methodology Acetone concentrations were measured by isotope-dilution purge and trap GC/MS. In isotope-dilution analysis, a species with two or more naturally occurring stable isotopes is analyzed in the presence of a standard in which one of the naturally occurring isotopes has been enriched. The concentration of the analyte is then determined from the measured isotope ratio. C-13 labeled acetone was used as the internal standard. The purge and trap system is a modified version of an instrument used for methyl bromide and alkyl nitrate analysis (Tokarczyk et al., 2003; Dahl et al., 2003). Seawater is injected into a calibrated volume and transferred under He pressure to a glass-fritted sparger. Sample injection volume for analysis was 0.6 mL for samples from 11/20/09 to 3/22/10 and increased to 4.2 mL for the remaining samples to test the robustness of the technique. Helium is sparged (100–150 mL·min−1) through the sample and the dissolved gases in He flow through a cold trap (−30 °C) to a glass bead cryotrap immersed in liquid nitrogen; the cold trap minimizes water reaching the liquid nitrogen trap. The trapped gases are thermally desorbed and transferred in He to the GC (Shimadzu, 14A) with a Poroplot Q column and into a quadruple mass spectrometer (HP 5973). A gas loop of a 1 ppm C-13 labeled internal acetone standard (Apel-Riemer Environmental Inc., Denver, Colorado) is added to the base of the sparger, and concentrations are calculated from the ratio of the unlabeled and labeled acetone peaks at m/e 58 and 61 respectively. In this experiment where we are following the loss of d-6 acetone, concentrations are determined from the ratio of d-6 acetone and c-13 labeled acetone at m/e 64 and 61 respectively. Standard volumes injected varied between 250 and 800 μL. This system has a detection limit of approximately 0.1 nM acetone for a 5 cm3 water sample. The measured precision during these experiments was ~2.5% across the range of spike concentrations used. 3. Results A total of 25 coastal water samples were collected over a 12 month period from November 2009 to November 2010 (Table 1). Salinities at the Santa Anna River Mouth averaged 26± 2 over this period, typical of this tidally-flushed estuarine environment that doesn't receive regular large fresh water inputs in the absence of rain events (Boehm et al., 2002). Temperatures at the time of sample collection were relatively consistent over the study time-frame, averaging 18± 1 °C. Decreases in salinity were observed in a few instances after isolated rain events and were generally associated with small temperature increases. Typical isotopically-labeled d-6 acetone concentrations as a function of time are shown in Fig. 1 for a 0.2 μm filtered and unfiltered water sample. Unfiltered samples will include loss from both abiotic reactions in the water and particulate phases and biological processing from bacteria in free-living and particle associated reactions, whereas degradation in filtered samples should primarily be due to abiotic, non-particle-mediated processes i.e. chemical reactions in solution. Initial spiked d-6 acetone concentrations were varied from 3 to 126 nM with an average of 59 ± 39 nM to cover the range of ambient
W.J. de Bruyn et al. / Marine Chemistry 150 (2013) 39–44 Table 1 Sampling dates and times, measured salinity (sal. in ppt), ambient temperature (Tw), initial spiked isotopically labeled acetone concentrations ([Ac], nM), and 1st order loss rate constants (k1). Date 11/20/09 12/11 1/06/10 1/11 1/13 1/19 3/10 3/15 3/22 4/05 4/12 4/19 4/21 4/26 5/03 5/05 5/10 5/12 8/03a 8/05a 8/09a 8/12a 10/10 10/21 11/02
Local time 14:00 18:00 7:50 7:55 7:55 7:55 6:45 6:50 6:50 6:40 6:50 6:40 6:40 6:50 6:40 6:50 6:50 6:55 8:07 7:11 6:48 8:07 10:15 10:15 8:50
Sal. 28.3 26.5 25.1 27.4 27.6 24.9 22.5 25.7 22.8 27.9 25.2 26.4 24.9 27.8 20.5 26.6 27.7 26.2 b b b b b b b
Tw (°C) c
18.8 17.9c 14.9c 16.4c 16.8c 15.9c 18.9c 17.0c 17.9c 16.3 16.3 18.0 17.5 16.5 19.0 18.8 17.5 18.9 16.8 17.7 18.1 15.3 18.9 18.9 18.1
[Ac] (nM)
k1 (hr−1)
89 102 62 98 91 126 42 63 53 21 4.9 4.4 53 27 5.2 16 3.2 31 72 51 118 45 15 28.7 263
0.09 ± 0.01 0.10 ± 0.02 0.13 ± 0.02 0.10 ± 0.01 0.12 ± 0.03 0.18 ± 0.02 0.09 ± 0.02 0.16 ± .02 0.15 ± 0.05 0.22 ± 0.02 0.17 ± 0.02 0.12 ± 0.01 0.15 ± 0.02 0.16 ± 0.01 0.20 ± 0.02 0.16 ± 0.03 0.15 ± 0.02 0.13 ± 0.04 0.084 ± 0.02 0.039 ± 0.025 0.033 ± 0.028 0.017 ± 0.005 0.047 ± 0.007 0.064 ± 0.008 0.060 ± 0.014
a
Water samples from NBP. No measurement made. c Samples incubated at room T (18–20 °C); remainder incubated at ambient water T measured at time of sampling. b
acetone concentrations found in a prior study in these waters (De Bruyn et al., 2012) and to probe the concentration dependence of the acetone loss kinetics. The solid lines in Fig. 1 are linear fits to the data shown for ease of viewing. First-order (exponential decay) rate constants were obtained from the slope of a plot of ln [acetone]0 / [acetone]t vs. time with an average R 2 value of 0.854; rate constants are given in Table 1. For the unfiltered samples, where both chemical and biotic and abiotic particle mediated loss processes occur, the average first-order rate constant was 0.12 ± 0.05 h −1. Errors are standard deviations of the slope of linear least squares fits to the first order loss data. Based on the average first-order rate constant, the corresponding half-life is 5.8 ± 2.4 h, where the half-life is given by ln 2/k for a first order process.
Fig. 1. Concentration of isotopically-labeled d-6 acetone ([Ac], in nM) as a function of time elapsed (in hr) for a typical split filtered (○) and unfiltered (●) seawater sample. Data shown for sample from 04/05/2010. Lines shown from linear regression fit to the data (filtered R2 = 0.291, p = 0.575; unfiltered R2 = 0.988, p = 0.0002).
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Changes in d-6 concentrations for the 0.2 μm filtered samples were minor relative to the changes described above for the unfiltered samples. Changes in acetone levels for filtered samples (i.e. abiotic rate only) were typically less than 10% of the observed changes for unfiltered samples, with an estimated average first-order rate constant of 0.005 ± 0.002 h −1 (standard error, n = 8) with a corresponding half-life of 139 ± 56 h. When samples were filtered through 0.8 μm filters instead of 0.2 μm, the unfiltered and filtered samples had similar loss rates within the uncertainties of the measurements suggesting that the species responsible for the loss are in the size range between 0.2 and 0.8 μm. In seawater, this size fraction includes both inorganic particles and bacteria, whereas zooplankton and dinoflagellates are in much larger size modes > 40 μm (Ahn and Grant, 2007). To confirm first-order kinetics, loss rates (changes in concentration as a function of time) were measured as a function of the initial spiked d-6 acetone concentration (Fig. 2). This was done for all samples collected in the morning at approximately the same time during the winter months at the Santa Anna River Mouth (16 out of 25 samples) to minimize seasonal and temporal variabilities. The observed positive linear relationship suggests that the kinetics is in fact first or pseudo first order. For the same subset of data, a plot (not shown) of first-order loss rate constants as a function of incubation temperature showed that temperature had minimal impact on the observed loss rate over the temperature range studied (10–30 °C; slope= −0.0021; int= 0.1996; R2 = 0.2505). Observed differences between average 10 °C data and 30 °C data were not significant at the 95% confidence limit (Student's t-test). Similarly, salinity had little impact on measured loss rates. A slight decrease in the observed first-order rate constant was observed as salinity increased from 20 to 28. A linear fit to the data had a slope of −0.0038, an intercept of 0.2401 and R2 = 0.0481; this was not a significant relationship over the salinity range observed in these coastal waters based on a p-test (p= 0.05). However, extrapolation to a salinity of 36 for seawater would give loss rates that are 36% lower. The slight decrease observed here is likely not directly due to salinity differences but rather to variability in particle concentrations or bacteria density and populations that co-vary with the same factors that impact salinity (e.g. rain events, tidal changes, etc.). 4. Discussion The acetone loss associated with small particles removed by filtration through 0.2 μm filters could be due to physical or biological processes, specifically physical adsorption to small particles or metabolism by
Fig. 2. Rates (nM·hr−1) as a function of the initial concentration of d-6 acetone (nM) added to the sample for all early morning samples. Line shown from linear regression fit to the data with slope = 0.0998 ± 0.0067 and intercept = 0.01 ± 0.37 (R2 = 0.971; p b 0.0001).
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bacteria. Suspended particle size distributions in these waters have been measured on seasonal and shorter time scales by light scattering and optical microscopy (Ahn et al., 2005; Ahn and Grant, 2007). Three types of particles have been identified; large plant and zooplankton debris (>200 μm); dinoflagellate particles (~40 μm); and inorganic particles b5 μm (Ahn and Grant, 2007). Increases in the fine particle mode (b5 μm) were typically associated with rainfall events, increased river discharges and increased fecal indicator bacteria (FIB) concentrations. Natural bacterial populations in marine coastal waters consist of both single-cell and colony forming bacterioplankton and are of diverse phylogenic origin, including subdivisions of the proteobacteria class and cytophaga-flexibacter-bacteroides phylum (Pinhassi et al., 1997; Pinhassi and Hagstrom, 2000). In addition, coastal waters adjacent to highly urbanized regions like Southern California receive inputs of FIB through runoff (Boehm et al., 2002). There have been no studies of natural marine bacterial populations at this beach, but many microbial water quality studies measuring FIB levels have been carried out in the surf zone waters at this site (for example Ahn et al., 2005 and references therein). The Orange County Sanitation District (OCSD) has a long-term monitoring program at this site which includes daily measurements of total coliform, fecal coliform and Enterococci. Variability in FIB in surf zone waters on both short and long time scales has been well documented (Boehm et al., 2002; Boehm, 2007). In general, bacteria levels are highest over the winter months (December through February) when rainfall levels are highest, and show decreases in summer and with locations farther from river outlets like the SAR (Boehm et al., 2002; OCSD). In Fig. 3, we show our measured first order particle-mediated loss rate constants as a function of time of year at HSB. All August 2010 data are for water samples from Newport Beach Pier taken for an ancillary study; however, in the summer dry season we expect these adjacent sites to be comparable to those of HSB because of the lack of high-volume riverine inputs and the long-shore currents that ensure rapid mixing of any low-volume runoff and wetland discharges (Grant et al., 2005). Also shown in Fig. 3 are discharge rates for the SAR (USGS; http://wdr.water.usgs.gov/wy2009/pdfs/ 11078000.2009.pdf; accessed 06/27/2012) over the same time period. Note that these are shown on a log scale for clarity of viewing, so stream flows in the winter wet season are 3 to 4 orders of magnitude higher than in the summer dry season. The observed seasonal cycling in river discharge rate is typical with what has been observed in prior studies (Boehm et al., 2002; OCSD). Increases in SAR flows are associated with the rain events that occurred in the wet season (from December through March). Southern California has a semi-arid
Fig. 3. First order loss rate constants (k1 in hr−1; ■) as a function of time of year. Superimposed on the data are river discharge stream gauge data every 5 days for the Santa Anna River from the United States Geological Survey (—; in ft3 s−1). Note that these are shown on a log scale for clarity of viewing so stream flows in the winter wet season are 3 to 4 orders of magnitude higher than in the summer dry season.
Mediterranean type climate with low annual rainfalls and sporadic rain events. Total monthly rainfall for the study period ranged from a high of 3.69″ in December 2009 to lows of 0″ from July through September 2010 (http://www.cnrfc.noaa.gov/monthly_precip_2010.php; accessed 6/27/2012). Monthly rainfall for the summer dry season from May through September 2010 averaged 0.002″ and was over 3 orders of magnitude higher at 2.5″ for the winter wet season from December 2009 through February 2010. While the acetone loss dataset does not cover the dry season extensively, rates are higher in the winter months during the rainy season when river water discharges are higher. Over the wet season, k1 averages 0.14 ± 0.04 h −1 whereas it is statistically significantly lower at 0.05 ± 0.02 h −1 over the dry season. These seasonal changes could be due to increases in loss efficiencies through increases in bacterial levels associated with runoff or to increased concentrations of small particles associated with increased river discharge (Ahn and Grant, 2007). FIB levels typically increase with a rain event and take a few weeks to return to baseline levels (Boehm et al., 2002). In addition to the FIB, there will also be marine bacteria in the water which should show similar seasonal variability. Increases and changes in marine bacterial populations might also be expected after rain events due to an influx of nutrients. Significant changes in the abundance of different marine bacteria over the year have been observed in coastal marine environments (Pinhassi et al., 1997) with distinct communities and lower levels of production observed in summer vs. fall and winter seasons. Another factor affecting natural bacterial populations is the near-shore coastal upwelling that typically occurs along the coast of Southern California from March through September, bringing in colder, nutrient rich waters from depth. This results in phytoplankton blooms which can be observed through satellite imaging. Different marine bacterial species have been observed to dominate during spring when phytoplankton blooms occur (Pinhassi et al., 1997). Upwelling events would explain the increases in loss rate constants in Spring and Summer 2010 that were not associated with significant increases in FIB levels and stream gauge flows due to large rainfall events. Any upwelling events would be indicated by a decrease in water temperatures. For example, k1 was 0.0839 h −1 on 8/4/2012 when water temperatures were 16.8 °C and 60% lower at 0.033 h −1 on 8/9/2012 when the water temperature was 18.1 °C. Similar effects were seen in early April when water temperatures dropped to 16.3 °C in association with an increase in k1 by 25% over typical levels for that time of year. Although we have limited samples taken at later times during the day, there appears to be a diurnal effect on the observed first order loss rate constants (Fig. 4), with higher values obtained during the early morning hours than the afternoon and evening. The early morning values for k1 average 0.14± 0.02 h−1 vs. the statistically lower average for the late morning and afternoon hours of 0.077 ± 0.02 h−1. These diurnal effects suggest that the observed decay is most likely due to consumption by bacteria rather than adsorption onto inorganic particles, since bacteria are affected by changing sunlight levels whereas inorganic particles should not be. It has been well-established at this beach that FIB undergo diurnal cycling; highest bacterial levels occur in the early morning, decrease to a minimum after solar noon and rebound at night (Boehm et al., 2002). These patterns have been attributed to bacterial mortality and oxidative stress associated with ultraviolet light and photochemically produced oxidants like hydrogen peroxide acting as sinks that vary with time of day (Boehm et al., 2002; Boehm, 2007), coupled with reseeding at night from the beach sediments and local wetland outflows as sources (Grant et al., 2001; Ahn et al., 2005; Yamahara et al., 2007). Few data have been published on the loss of acetone in seawater. Rathbun et al. (1982) measured acetone consumption by cultured sewage bacteria in an Oceanography International E/BOD respirator. They report a first order decay rate of 0.163 ± 0.102 h−1 in experiments
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Acknowledgments The authors thank the National Science Foundation (OCE # 0727614) for funding this work. References
Fig. 4. Diurnal variability in first-order loss rate constants (■; hr−1) as a function of local time. Also shown on the plot are solar irradiation levels (straight line; W m−2) at the same site reproduced from data in Clark et al. (2009).
in which the culture was not pretreated with acetone, and a rate of 0.058 ± 0.046 h−1 when the sample was pretreated. Initial concentrations in their study were 0.27 to 2.7 mM. They suggest that the rates in the real world would be lower because of the idealized conditions of the experiment. While we can't conclusively state that our observed loss rate is due solely to bacteria and not also inorganic particles, the average first order rate constant of 0.12± 0.05 h−1 we measured here for natural seawater compares well with their measurements in bacterial cultures. Biological loss rates for methanol, another oxygenated hydrocarbon, recently measured in the open ocean are lower than the rates obtained for acetone. Dixon et al. (2011a) report biological oxidation rates for methanol of 2.1 to 8.4 nM·day −1 in surface waters of the northeast Atlantic with surface concentrations of 70–97 nM and 2–146 nM·day −1 in the tropical Atlantic with surface concentrations of 300 nM. Based on their data, we estimate the associated approximate first order rate constants to be 0.001–0.004 h −1 for the northeast Atlantic and 0.0003–0.02 h −1 for the tropical Atlantic. These are 2 to 3 orders of magnitude lower than what we measured in this study for acetone. This difference could partially be attributed to the difference in the environments the measurements were made in, since open ocean waters have significantly lower bacterial population densities and diversity than near-shore waters.
5. Conclusions Acetone can be produced and destroyed in seawater. In theory, removal can occur via a combination of chemical, photochemical and particle-mediated loss pathways (including biological consumption). We measured acetone loss rates in seawater samples from a coastal site in Southern California. Our loss rates for filtered samples (attributed to abiotic, non-particle-mediated rates i.e. chemical processes only) were on the order of 10% or less than the observed loss rates for unfiltered seawater samples (attributed to biotic and abiotic processes like bacterial metabolism and particle sorption). The average first-order loss rate constant measured for unfiltered samples was 0.12±0.05 h−1. Seasonal and temporal trends were observed, with higher loss rate constants measured on average: 1) in the rainy winter wet season vs. the dry summer season; 2) after rain and upwelling events; and 3) earlier in the day. These trends are consistent with established patterns and changes in bacterial levels, suggesting that loss may be due primarily to bacteria rather than non-organic particles.
Ahn, J.H., Grant, S.B., 2007. Size distribution, sources and seasonality of suspended particles in southern California marine bathing waters. Environ. Sci. Technol. 41, 695–702. Ahn, J.H., Grant, S.B., Surbeck, C.Q., Digiacomo, P.M., Nezlin, N.P., Jiang, S., 2005. Coastal water quality impact of stormwater runoff from an urban watershed in southern California. Environ. Sci. Technol. 39, 5940–5953. Arnold, S.R., Chipperfield, M.P., Blitz, M.A., Heard, D.E., Pilling, M.J., 2004. Photodissociation of acetone: atmospheric implications of temperature-dependent quantum yields. Geophys. Res. Lett. 31, LO7110. http://dx.doi.org/10.1029/2003GLO19099. Beale, R., Liss, P.S., Nightingale, P.D., 2010. First oceanic measurements of ethanol and propanol. Geophys. Res. Lett. 37, L24607. http://dx.doi.org/10.1029/2010GL045534. Boehm, A.B., 2007. Enterococci concentrations in diverse coastal environments exhibit extreme variability. Environ. Sci. Technol. 41, 8227–8232. Boehm, A.B., Grant, S.B., Kim, J.H., Mowbray, S.L., McGee, C.D., Clark, C.D., Foley, D.M., Wellman, D.E., 2002. Decadal and shorter period variability of surf zone quality at Huntington Beach, California. Environ. Sci. Technol. 36, 3885. Brasseur, G.P., Hauglustaine, D.A., Walters, S., Rasch, P.J., Muller, J.F., Granier, C., Tie, X., 1998. MOZART, a global chemical transport model for ozone and related chemical tracers: 1. Model description. J. Geophys. Res. 103, 28,265–28,289. Clark, C.D., De Bruyn, W.J., Hirsch, C.M., Jakubowski, S.D., 2009. Hydrogen peroxide measurements in recreational marine bathing waters in Southern California, USA. Water Res. 44, 2203–2210. Collins, W.J., Stevenson, D.S., Johnson, C.E., Derwent, R.G., 1999. Role of convection in determining the budget of odd hydrogen in the upper troposphere. J. Geophys. Res. 104, 26,927–26,941. Dahl, E.E., Saltzman, E.S., De Bruyn, W.J., 2003. A mechanism for the aqueous phase production of alkyl nitrates in seawater. Geophys. Res. Lett. 36, 1271–1275. De Bruyn, W.J., Clark, C.D., Pagel, L., Takahara, C., 2011. Photoproduction of formaldehyde, acetaldehyde and acetone from chromophoric dissolved organic matter in coastal and estuarine waters. J. Photochem. Photobiol. 226, 16–22. De Bruyn, W.J., Clark, C.D., Pagel, L., 2012. Oxygenated Hydrocarbons in Coastal Waters, Book Chapter in Oceanography. In-Tech Open Access Publishing978-953-307-919-6. de Gouw, J.A., Middlebrook, A.M., Warneke, C., Goldan, P.D., Kuster, W.C., Roberts, J.M., Fehsenfeld, F.C., Worsnop, D.R., Canagaratna, M.R., Pszenny, A.A.P., Keene, W.C., Marchewka, M., Bertman, S.B., Bates, T.S., 2005. Budget of organic carbon in a polluted atmosphere: Results from the New England Air Quality Study in 2002. J. Geophys. Res. Atmos. (1984–2012), 110 (D16). Dixon, J.L., Beale, R., Nightingale, P.D., 2011a. Rapid biological oxidation of methanol in the tropical Atlantic: significance as a microbial carbon source. Biogeosci. Discuss. 8, 3899–3921. Dixon, J.L., Beale, R., Nightingale, P.D., 2011b. Microbial methanol uptake in the northeast Atlantic waters. ISME J. 5, 704–716. Dufour, G., Szopa, S., Hauglustaine, D.A., Boone, C.D., Rinsland, C.P., Bernath, P.F., 2007. The influence of biogenic emissions on upper-tropospheric methanol as revealed from space. Atmos. Chem. Phys. 7, 6119–6129. Elias, T., Szopa, S., Zahn, A., Schuck, T., Brenninkmeijer, C., Sprung, D., Slemr, F., 2011. Acetone variability in the upper troposphere: analysis of CARABIC observations and LMDZ-INCA chemistry-climate model simulations. Atmos. Chem. Phys. 11, 8053–8074. Finlayson-Pitts, B.J., Pitts, J.N., 1999. Chemistry of the Upper and Lower Atmosphere: Theory, Experiments, and Applications. Elsevier Science & Technology Books. Grant, S.B., Sanders, B.F., Boehm, A.B., Redman, J.A., Kim, J.H., Mrse, R.D., Chu, A.K., Gouldin, M., McGee, C.D., Gardiner, N.A., Jones, B.H., Svejkovsky, J., Leipzig, G.V., Brown, A., 2001. Generation of Enterococci bacteria in a coastal saltwater marsh and its impact on surf zone water quality. Environ. Sci. Technol. 35, 2407–2416. Grant, S.B., Kim, J.H., Jones, B.H., Jenkins, S.A., Wasyl, J., Cudaback, C., 2005. Surf zone entrainment, along-shore transport and human health implications of pollution from tidal outlets. J. Geophys. Res. 110, C10025. http://dx.doi.org/10.1029/2004JC002401. Jacob, D.J., Field, B.D., Jin, E.M., Bey, I., Li, Q., Logan, J.A., Yantosca, R.M., 2002. Atmospheric budget of acetone. J. Geophys. Res. 107 (D10), 4100. http://dx.doi.org/10.1029/ 2001JD000694. Kameyama, S., Tanimoto, H., Inomata, S., Tsunoga, U., Ooki, A., Takeda, S., Obata, H., Tsuda, A., Uematsu, M., 2010. High-resolution measurement of multiple volatile organic compounds dissolved in seawater using equilibrator inlet–proton transfer reaction-mass spectrometry (EI–PTR-MS). Mar. Chem. 122, 59–73. Kieber, D.J., Mopper, K., 1987. Photochemical formation of glyoxylic and pyruvic acids in seawater. Mar. Chem. 21, 135–149. Kieber, R.J., Mopper, K., 1990. Determination of picomolar concentrations of carbonyl compounds in natural waters, including seawater, by liquid chromatography. Environ. Sci. Technol. 24, 1477–1481. Kieber, R.J., Zhou, X., Mopper, K., 1990. Formation of carbonyl compounds from UVinduced photodegradation of humic substances in natural waters: fate of riverine carbon in the sea. Limnol. Oceanogr. 35, 1503–1515. Marandino, C.A., DeBruyn, W.J., Saltzman, E.S., Miller, S.D., Prather, M.J., 2005. Oceanic uptake and the global atmospheric budget of acetone. Geophys. Res. Lett. 32, L15806. http://dx.doi.org/10.1029/2005GL023285. Millet, D.B., Jacob, D.J., Custer, T.G., de Gouw, J.A., Goldstein, A.H., Karl, T., Singh, H.B., Sive, B.C., Talbot, R.W., Warneke, C., Williams, J., 2008. New constraints on terrestrial and oceanic sources of atmospheric methanol. Atmos. Chem. Phys. 8, 6887–6905.
44
W.J. de Bruyn et al. / Marine Chemistry 150 (2013) 39–44
Millet, D.B., Guenther, A., Siegel, D.A., Nelson, N.B., Singh, H.B., de Gouw, J.A., Warneke, C., Williams, J., Erdekens, G., Sinha, V., Karl, T., Flocke, F., Apel, E., Riemer, D.D., Palmer, P.I., Barkley, M., 2010. Global atmospheric budget of acetaldehyde: 3-D model analysis and constraints from in situ and satellite observations. Atmos. Chem. Phys. 10, 3405–3425. Mopper, K., Stahovec, W.L., 1986. Sources and sinks of low molecular weight organic carbonyl compounds in seawater. Mar. Chem. 19, 305–321. http://dx.doi.org/ 10.1016/0304-4203(86)90052-6. Naik, V., Fiore, A.M., Horowitz, L.W., Singh, H.B., Wiedinmeyer, C., Guenther, A., de Gouw, J.A., Millet, D.B., Goldan, P.D., Kuster, W.C., Goldstein, A., 2010. Observational constraints on the global atmospheric budget of ethanol. Atmos. Chem. Phys. Discuss. 10, 925–945. Nemecek-Marshall, M., Wojciechowski, C., Kuzma, J., Silver, G.M., Fall, R., 1995. Marine vibrio species produce the volatile organic compound acetone. Appl. Environ. Microbiol. 61, 44–47. Pinhassi, J., Zweifel, U.L., Hagstrom, A., 1997. Dominant marine bacteriaplankton species found among colony-forming bacteria. Appl. Environ. Microbiol. 63, 3359–3366. Pinhassi, J., Hagstrom, A., 2000. Seasonal succession in marine bacterioplankton. Aquat. Microb. Ecol. 21, 245–256 [Published june 15]. Rathbun, R.E., Stephens, D.W., Schultz, D.J., Tai, D.Y., 1982. Fate of acetone in water. Chemosphere 11, 1097–1114. Schade, G.W., Goldstein, A.H., 2006. Seasonal measurements of acetone and methanol: abundances and implications for atmospheric budgets. Global Biogeochem. Cycles 20, GB1011. http://dx.doi.org/10.1029/2005GB002566. Singh, H.B., O'Hara, D., Herlth, D., Sachse, W., Blake, D.R., Bradshaw, J.D., Kanakidou, M., Crutzen, P.J., 1994. Acetone in the atmosphere: distribution sources and sinks. J. Geophys. Res. 99, 1805–1819. Singh, H., Chen, Y., Tabazedeh, A., Fukui, Y., Bey, I., Yantosca, R., Jacob, D., Arnold, F., Wohlfrom, K., Atlas, E., Flocke, F., Blake, D., Blake, N., Heikes, B., Snow, J., Talbot, R., Gregory, G., Sachse, G., Vay, S., Kondo, Y., 2000. Distribution and fate of selected oxygenated organic species in the troposphere and lower stratosphere over the Atlantic. J. Geophys. Res. 105, 3795–3806.
Singh, H., Chen, Y., Staudt, A., Jacob, D., Blake, D., Heikes, B., Snow, J., 2001. Evidence from the Pacific troposphere for large global sources of oxygenated organic compounds. Nature 410, 1078–1081. Singh, H.B., Slas, L.J., Chatfield, R.B., Czech, E., Fried, A., Walega, J., Evans, M.J., Field, B.D., Jacob, D.J., Blake, D., Heikes, B., Talbot, R., Sachse, G., Crawford, J.H., Avery, M.A., Sandholm, S., Fuelberg, H., 2004. Analysis of atmospheric distribution sources and sinks of oxygenated volatile organic chemicals based on measurements over the Pacific during TRACE-P. J. Geophys. Res. 109, D15S07. http://dx.doi.org/ 10.1029/2003JD003883. Sluis, M.K., Ensign, S.A., 1997. Purification and characterization of acetone carboxylase from Xanthobacter strain Py2. Proc. Natl. Acad. Sci. 94, 8456–8461. Tokarczyk, R., Goodwin, K., Saltzman, E.S., 2003. Methyl chloride and methyl bromide degradation in the southern ocean. Geophys. Res. Lett. 1808, 30. http://dx.doi.org/ 10.1029/2003GLO17459. Wakeham, S.G., Davis, A.C., Karas, J.L., 1983. Mesocosm experiments to determine the fate and persistence of volatile organic compounds in coastal seawater. Environ. Sci. Technol. 17, 611–617. Wang, Y., Jacob, D.J., Logan, J.A., 1998. Global simulation of tropospheric O 3–NO xhydrocarbon chemistry. J. Geophys. Res. 103, 10,713–10,726. Weyer, E.R., Rettger, L.F., 1927. A comparative study of six different strains of the organism commonly concerned in large-scale production of butyl alcohol and acetone by the biological process. J. Bacteriol. 14 (6), 399–424 (PMCID: PMC374969 ). Williams, J., Holzinger, R., Gros, V., Xu, X., Atlas, E., Wallace, D.W.R., 2004. Measurements of organic species in air and seawater from the tropical Atlantic. Geophys. Res. Lett. 31, L23S06. http://dx.doi.org/10.1029/2004GL020012. Yamahara, K.M., Layton, B.A., Santoro, A.E., Boehm, A.B., 2007. Beach sands along the California Coast are diffuse sources of fecal bacteria to coastal waters. Environ. Sci. Technol. 41, 4515–4521. Zhou, X., Mopper, K., 1997. Photochemical production of low-molecular-weight carbonyl compounds in seawater and surface microlayer and their air-sea exchange. Mar. Chem. 56, 201–213.