Saccharide composition in atmospheric particulate matter in the southwest US and estimates of source contributions

Aerosol Science 41 (2010) 62 -- 73

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Saccharide composition in atmospheric particulate matter in the southwest US and estimates of source contributions Yuling Jiaa, b , Andrea L. Clementsa, b , Matthew P. Fraserb, ∗ a b

Department of Civil and Environmental Engineering, Rice University, Houston, TX, USA Global Institute of Sustainability, Arizona State University, PO Box 875402, Tempe, AZ 85287, USA

A R T I C L E

I N F O

Article history: Received 6 February 2009 Received in revised form 11 August 2009 Accepted 13 August 2009 Keywords: Saccharides PM Source Eastern Texas Central Arizona

A B S T R A C T

Saccharide compositions were measured in ambient particulate matter (PM) samples collected at four sites in Eastern Texas and Central Arizona in an effort to assess the contribution from biomass burning, atmospheric entrainment of soil, and primary biological aerosol particles (PBAPs) in regions with different climate patterns and ecosystems. In spite of the concentration difference, samples from the four study sites showed similar saccharide composition and seasonal variation, with the only exception being trehalose, likely resulting from the influence of local climatic conditions. Comparison of samples at the Arizona site showed different saccharide enrichment patterns between PM2.5 and PM10, which is consistent with their proposed sources as determined by a correlation analysis between observations. A positive matrix factorization (PMF) model was used to resolve three saccharide-related source factors and their relative source contributions to ambient PM using saccharides as tracers. Both the correlation and PMF model results indicate a stronger influence from local biogenic sources on aerosol saccharides at the rural sites than the urban site in Texas, and a greater impact from the PBAP and other biologically derived sources for PM collected in the Arizona location. This paper will provide the first analysis of saccharides in both fine and coarse PM in two US regions with dramatically different climates and ecosystem and provide a characterization of the ambient aerosol sources. © 2009 Elsevier Ltd. All rights reserved.

1. Introduction Saccharide compounds are important constituents of ambient aerosols. Approximately 13–26% of the total compound mass identified in continental aerosols were saccharides and this number can reach as high as 63% in oceanic aerosols (Simoneit, Elias et al., 2004; Simoneit, Kobayashi et al., 2004). Saccharides in aerosols have been proposed as tracers for the sources, processes and transport of biologically important organic material in the natural environment (Medeiros & Simoneit, 2007). Recent studies have identified saccharides in emissions from biomass burning (Fine, Cass, & Simoneit, 2004; ; Schmidl et al., 2008; Simoneit, Elias et al., 2004; Simoneit, Kobayashi et al., 2004), atmospheric entrainment of soil and associated biota (Simoneit, Elias et al., 2004; Rogge, Medeiros, & Simoneit, 2006, 2007), and more recently primary biological aerosol particles (PBAPs) (Bauer, Schueller et al., 2008; Caseiro et al., 2007; Elbert, Taylor, Andreae, & Poschl, 2007;; Graham et al., 2003). Specifically, biomass burning aerosols include anhydrous saccharides (levoglucosan, mannosan and galactosan) generated from the combustion and pyrolysis of cellulose and hemicellulose, and possibly sugar polyols from thermal stripping during burning (Simoneit, 2002; Simoneit, Elias et al., 2004; Simoneit et al., 1999). Levoglucosan has been tested and confirmed as a good tracer for the long range transport of this ∗ Corresponding author. Tel.: +1 480 965 3489. E-mail address: [email protected] (M.P. Fraser). 0021-8502/$ - see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaerosci.2009.08.005

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source category (Fraser & Lakshmanan, 2000). Soil and associated biota contributes to ambient aerosols through resuspension by wind erosion or agricultural practices (Cox & Wathes, 1995; Simoneit, Elias et al., 2004). Saccharide compounds measured in emissions from this category include a variety of monosaccharides, disaccharides, and sugar polyols, among which glucose, sucrose, and trehalose were proposed as marker compounds in a study of soils from five types of crop fields in the San Joaquin Valley of California (Rogge et al., 2007). PBAPs are biologically derived material such as spores, pollens, fungi, algae, protozoa, bacteria, viruses and fragments of plants and animals (Elbert et al., 2007; Caseiro et al., 2007; Winiwarter, Bauer, Caseiro, & Puxbaum, 2009). They contribute to ambient aerosols through direct injection into the atmosphere (Jaenicke, 2005), and a large array of aerosol saccharides have been reported to originate from PBAPs (Bieleski, 1982; Graham et al., 2003; Lewis & Smith, 1967; Pacini, Guarnieri, & Nepi, 2006). In particular, mannitol and arabitol have been proposed as tracers for airborne fungal spores (Bauer et al., 2008; Elbert et al., 2007). The contributions of these three sources (biomass burning, atmospheric entrainment of soil and associated biota, and PBAPs) have been shown to be significant sources of saccharides to ambient PM. The 1999 National Emission Inventory estimated that biomass burning and atmospheric entrainment of soil and fugitive dust contributes 20.6 millions of tons per year to PM10 and 4.4 millions of tons per year to PM2.5 in the United States (McMurry, Shepherd, & Vickery, 2004). Chow et al. (1992) and Chen, Watson, Chow, and Magliano (2007) used multi-variate receptor models based on ions and element markers to estimate that up to 40–60% of the ambient PM10 and 7–23% of the ambient PM2.5 at the San Joaquin Valley in California were derived from fugitive dust. Estimates of emissions of PBAPs on the global scale range from 56 Tg (Penner, Andreae, Annegarn, and Barrie 2001) to 1000 Tg (Jaenicke, 2005) annually. Bauer, Schueller et al. (2008) used spore counts and concentrations of mannitol and arabitol to estimate the fungal contribution to PM10 in Vienna, Austria of between 3% and 7% at a suburban sampling location. However, still very little is known about the contribution of soil dust and PBAPs to aerosol mass, particularly on a regional scale. In recognition to the role of aerosol saccharides as indicators of major aerosol sources, this study was undertaken to characterize and compare the saccharide composition of ambient PM in two different regions of the continental United States. A series of PM2.5 samples were first collected at two rural sites (San Augustine and Clarksville) and one urban site (Dallas) in Eastern Texas from November 2005 to July 2006. Following that, PM2.5 and PM10 samples were simultaneously collected in Higley, Arizona, a suburb of the Phoenix metropolitan area which routinely exceeds the federal 24 hr NAAQS (National Ambient Air Quality Standards) for PM10 (AirData, 2008). The goal of this study was to resolve the aerosol saccharide composition at four different sites, to compare the saccharide profiles between the fine and coarse fractions of PM, and to assess the contribution of biologically derived sources including biomass burning, atmospheric entrainment of soil, and PBAPs to ambient PM using saccharide compounds as indicators. This will provide the first analysis of saccharides in both fine and coarse PM in the arid Southwest US, and comparison of saccharides in fine PM in two US regions with dramatically different climates and ecosystems.

2. Experimental method 2.1. Ambient sampling Ambient PM samples were collected on pre-baked quartz-fiber filters (Whatman, 8×10 ) by high-volume air samplers (Thermo) equipped with a size selective inlet (MSP Corp) to sample PM2.5. Samples were taken at a flow rate of 1200 LPM for a total of 24 hrs on each sampling day and used for carbonaceous and ionic compositional analysis. In parallel, PM was also collected on pre-weighed Teflon-filters (Whatman, 47 mm) using low-volume air samplers (Thermo, Partisol-Plus, Model 2025). These low volume Teflon-filter samples were taken at a flow rate of 16.7 LPM for 24 hrs on each sampling day and used for gravimetric mass determination. After collection, quartz-fiber filter samples were returned from the field sites in glass jars with Teflon-lined caps and Teflon-filters were transported in dedicated Petri-dishes. All samples were stored in freezers at −4 F until analysis. Sampling in Texas was conducted at three sites between November 2005 and July 2006. Of the sites (Fig. 1), San Augustine (31◦ 32 N, 94◦ 10 W, EPA Site no. 48-405-0646) and Clarksville (33◦ 37 N, 95◦ 3 W, EPA Site no. 48-387-0648) were located in rural areas of eastern Texas surrounded by grasslands and trees, and the Dallas sampling site (32◦ 49 N, 96◦ 51 W, EPA Site no. 48-113-0069) was located in the urban core of that city and within 1-mile distance to highway 77 and interstate 35. Samples were taken every third day at each site, and a total of 174 PM2.5 samples were obtained for analysis. During this sampling period, a series of wildfires broke out in northern Texas and southern Oklahoma from November 2005 to April 2006, with a reported tens of thousands of wildfires and millions of acres of land and forest were burned during this period (NCDC, 2007). Sampling in central Arizona was conducted from January to April 2008 at Higley (33◦ 18 N, 111◦ 43 W, EPA Site no. 04-0134006), a location of urban growth in a traditionally agricultural location (Fig. 1). This site is surrounded by agricultural and bare lands, and is adjacent to a dirt road and a railway track. Both PM2.5 and PM10 samples were taken by methods equivalent to the above described sampling every other day, and a total of 45 PM2.5 and 46 PM10 samples were obtained.

2.2. Sample analysis 2.2.1. Element carbon (EC) and organic carbon (OC) analysis The elemental and organic carbon content was determined for the ambient aerosol samples using a Sunset Laboratory Thermo-Optical Carbon Analyzer following the thermal-optical method described by Birch and Cary (1996).

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Fig. 1. Map of sampling locations in Texas and Arizona, USA. Left: three sampling sites in Texas, including two rural sites (Clarksville and San Augustine) and one urban site (Dallas); Right: sampling site in Central Arizona (Higley).

2.2.2. Gravimetric analysis Total mass of each collected aerosol sample was determined using a microbalance. The low volume Teflon-filters were weighed under controlled temperature (22−24 ◦ C) and humidity conditions (45–55%) both before and after sampling to obtain aerosol mass loadings. 2.2.3. Organic speciation One fourth of the 8×10 quartz-fiber filter with collected sample was extracted and analyzed for sugar composition following the method described by Medeiros and Simoneit (2007), which has been shown to be highly efficient for extracting sugar compounds (Medeiros & Simoneit, 2007). An isotopically labeled internal standard (D-Glucose-1,2,3,4,5,6,6-d7) was spiked to the sample, samples were extracted three times for 10 min each with dichloromethane:methanol (2:1, v/v) under mild ultrasonic agitation, and the solvent extract was combined, filtered, and concentrated using a rotary evaporator, and then blown down to complete dryness using pure nitrogen gas. Extracted saccharides were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) containing 1% trimethylchlorosilane (TMCS) and pyridine for 3 h at 70 ◦ C, and the converted trimethylsilyl derivatives were analyzed by GC/MS within 24 h. A 1 l aliquot of the derivatized extracts were analyzed by a HP model 6890 gas chromatography (GC) coupled to a HP model 5973 mass selective detector (MSD). An aliquot of 1-phenyldodecane (1-PD) was co-injected to ensure proper injection as well as for independently monitoring instrument response. Separation was achieved using a 30 m HP-5MS capillary column. The GC operating conditions were as follows: temperature hold at 65 ◦ C for 10 min, increase from 65 to 300 ◦ C at a rate of 10 ◦ C/min with a final isothermal hold at 300 ◦ C for 5 min. The sample was injected splitless with the injector temperature at 250 ◦ C. The MS was operated in electron impact mode at 70 eV and scanned from 50 to 500 Dalton. Individual sugar compounds were identified by the comparison of mass spectra to authentic standards, literature and library data, and interpretation of mass spectrometric fragmentation patterns. Compounds were quantified using selected ion peak area and converted to compound mass using relative response factors (RRF) determined by GC/MS injection of authentic standards spanning the range of concentrations of ambient samples and 1-PD under the same instrumental operating conditions. 3. Results and discussion 3.1. Total saccharides, PM mass and organic carbon in PM2.5 Total measured saccharide concentrations, PM mass and organic carbon for PM2.5 samples collected at all four sites were summarized in Table 1. In general, much lower saccharide concentrations were measured at the Arizona site than at the three Texas sites, due to a lower PM2.5 and the fraction of PM2.5 that is organic carbon, possibly as a result of the arid desert location. However, the average fraction of PM2.5 mass and OC that was quantified as saccharides at Higley was comparable to that measured at Dallas (Table 1), consistent with the fact that both sites are located in a metropolitan area, but in spite of the local climatic and ecological conditions. Among the three sampling sites in Texas, total measured saccharides were higher at the two rural sites (San Augustine and Clarksville) than the urban site, which is consistent with less contribution from biogenic sources at the urban location. This corroborates the suggested role of saccharides as tracers for biologically derived sources (Bauer et al., 2008; Bauer, Schueller et al., 2008; Graham et al., 2003; Simoneit, Elias et al., 2004; Simoneit et al., 1999).

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Table 1 Total measured saccharide concentrations, PM mass and organic carbon in PM2.5 samples at one suburban site (Higley) in Arizona, and two rural sites (San Augustine and Clarksville) and one urban site (Dallas) in Texas.

Total measured saccharide concentration (ng/m3 ) PM2.5 Mass (ug/m3 ) OC (ug/m3 ) Total Saccharides/PM2.5 (%) Total Saccharides/OC (%)

Higley, AZ (January–April 2008) (n = 45)

San Augustine, TX (November 2005– July 2006) (n = 76)

Clarksville, TX (January–July 2006) (n = 40)

Dallas, TX (January–July 2006) (n = 57)

1.1−83.0 (24.1)

15.4−355.1 (70.4)

7.5−372.2 (128.4)

15.8−196.0 (52.4)

1.1−12.4 (5.9) 0.7−2.9 (1.6) 0.02−2.0 (0.5) 0.1−5.2 (1.5)

2.5−23.2 (9.9) 1.2−9.1 (2.6) 0.2−1.7 (0.8) 0.5−10.2 (3.3)

2.2−22.3 (10.2) 1.3−9.6 (3.2) 0.1−6.0 (1.6) 0.2−13.4 (5.2)

3.5−34.0 (11.2) 1.8−6.5 (3.2) 0.1−1.6 (0.6) 0.7−4.1 (2.0)

*Numbers in parenthesis are means of values; n = total number of samples analyzed.

Table 2 Comparison of total measured saccharide concentrations and ratios to OC in literature. Location

Sampling period

Concentration range (ng m−3 )

% of OC

Source

Hong Kong University campus

38−129 (84) 83−175 (133) 70−1316 (375) 88−683 (292) 10−180

0.6−2.2 (1.3) 0.5−1.4 (1.1) 0.3−3.6 (1.5) 0.6−1.5 (1.1) –

Wan and Yu (2007)

Howland experimental forest, Maine

Spring Summer Fall Winter May–October

Curbside site, Norway Urban background site, Norway Suburban site, Norway Rural background site, Norway Amazonia, Brazil San Joaquin Valley, CA

September–October November–December January–March, May–June January–December July December–next January

17−134 10−537 14−1085 1−43 32−115 (61) 144−3644

0.1−0.3 (0.2) 0.1−0.8 (0.2) 0.1−1.7 (0.5) 0.1−1.0 (0.2) 5.4% –

Yttri et al. (2007)

Medeiros, Conte, Weber, & Simoneit (2006)

Graham et al. (2003) Nolte et al. (2001)

*Numbers in parenthesis are means of values.

The total measured saccharide concentrations at Higley were lower than literature reports with the only comparable ambient levels measured at a rural background site in Norway (Table 2). The total measured saccharide concentrations at the three sites in Texas were comparable to several measurements conducted elsewhere, including those measured at the Howland experimental forest in Maine, a roadway site and an urban background site in Norway, and in the Amazon basin in Brazil, but were lower than those observed in the urban setting in Hong Kong, a suburban site in Norway, and the San Joaquin Valley in California (Table 2). However, when considering the corresponding OC levels, the AZ suburban site (Higley) and the TX urban site (Dallas) were comparable to measured levels in Hong Kong, and the two TX rural sites (San Augustine and Clarksville) had higher percentages of total measured saccharides to OC than most of the places with the exception of the tropic Amazonia site. This suggests that saccharide compounds represent a higher proportion of the organic carbon content in aerosols collected in rural areas, and in particular those locations with active biological production. 3.2. Seasonal variations of saccharide compounds in PM2.5 Aerosol concentrations of individual saccharide compounds varied widely with the local season. Fig. 2 shows the monthly variation of the measured major saccharide compounds. For the three Texas sites, approximately 10 24 h samples were analyzed each month, and for the Higley site in Arizona, approximately 15 24 h samples were analyzed each month. Of the measured saccharide compounds, levoglucosan was measured at the highest concentrations at all four sites, constituting more than half of the total measured saccharide concentrations in most of the samples. Levoglucosan levels were elevated in the first half of each sampling period, indicating the enhanced biomass burning activities in winter and early spring (Simoneit, Elias et al., 2004), which dropped in late spring and summer in both sampling regions. The levoglucosan levels at the three sites in Texas also followed reports of the Texas-Oklahoma wildfires from November 2005 to April 2006 (Fig. 2), confirming the impact from biomass burning. Glucose and sucrose were the second most abundant saccharide compounds, both of which had higher concentrations in spring. In particular, sucrose was dominant almost exclusively in March and April. Sucrose is an important sugar in developing flower buds (Bieleski, 1995) and a known component of pollen grain (Pacini, 2000), and the high aerosol sucrose in March and April suggested the origin of this compound from pollen or pollen fragment sources. Glucose is the simple sugar present in vascular plants (Cowie & Hedges, 1984) and serves as a primary carbon reservoir for plants and microorganisms (Pigman & Horton, 1980). Consistent with this role, the increase of glucose measured in aerosols during the growing season, was expected. Another important sugar measured in all PM2.5 samples was trehalose, a primary saccharide serving as a stress protectant in bacteria, yeast, insects and a few higher plants (Caseiro et al., 2007). Trehalose measured in the Texas samples was elevated during the summer months (May, June and July), and a similar trend was observed for two major sugar polyols, mannitol

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Glucose 60 Higley

50

San Augustine Clarksville

ng/m3

40

Dallas

30 20 10

Jul

Jun

May

Apr

Mar

Trehalose

45 40 35 30 25 20 15 10 5 0

ng/m3

8 7

Higley

6

San Augustine

5

Clarksville Dallas

4 3 2 1

Mannitol

Ju l

N

ov De c Ja n Fe b M ar Ap r M ay Ju n

Jul

Jun

May

Apr

Mar

Feb

Jan

Dec

0

Nov

ng/m3

Sucrose

Feb

Jan

Dec

Nov

Jul

Jun

May

Apr

Mar

Feb

Jan

Dec

0

Nov

ng/m3

Levoglucosan 100 90 80 70 60 50 40 30 20 10 0

Arabitol

30

12

25

10

20

8

Dallas

Jul

Jun

May

Apr

Mar

Feb

Jan

Dec

Jul

Jun

0

May

0

Apr

2

Mar

5

Feb

4

Jan

Clarksville

6

10

Dec

San Augustine

Nov

ng/m3

15

Nov

ng/m3

Higley

Fig. 2. Seasonal variation of major saccharide compounds at one suburban site (Higley) in Arizona, and two rural sites (San Augustine and Clarksville) and one urban site (Dallas) in Texas (for each month, n∼10 for San Augustine, Clarksville and Dallas, and n∼15 for Higley, n = number of 24 hr sample analyzed).

and arabitol, an indication of the contribution from fungal spore derived sources (Bauer et al., 2008; Dahlman, Persson, Nasholm, & Palmqvist, 2003;; Elbert et al., 2007; Eleutherio, Araujo, & Panek, 1993; Graham et al., 2003; Lewis & Smith, 1967). For the Arizona site, no samples were available after April to show the comparable trend, but trehalose was elevated throughout the sampling period from January to April. As these concentrations were equal or greater than trehalose measured at the three sites in Texas during the same period of the year while the concentrations of other fine aerosol saccharides measured in Arizona were much lower than those measured at the three Texan sites, this may suggest a unique influence from the desert environment and drought conditions on the metabolic activities of micro-organisms and plants in Arizona. The seasonal variation of saccharide compounds in PM2.5 have been reported in previous studies (Medeiros, Conte, Weber, & Simoneit, 2006; Wan & Yu 2007; Yttri, Dye, & Kiss, 2007), and, in general, good agreements were found between the results of current study and literature reports with a few exceptions. For example, in Hong Kong fine aerosol, levoglucosan concentrations were enhanced in both fall and winter, and sucrose was measured at the highest concentrations in autumn as opposed to spring (Wan & Yu, 2007). In PM2.5 samples at one suburban site in Norway, higher concentrations of glucose were measured in winter compared to summer (Yttri et al., 2007). These results can be interpreted as indicators of ecosystem function, climate and local sources, i.e., the enhancement of levoglucosan measured in Hong Kong as a result of crop residue burning during the harvest season, and more incidents of hill fires during the drier weather of fall (Wan & Yu, 2007); the peak of sucrose in Hong Kong

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Average concentration of saccharide compounds in PM2.5 and PM10 - Higley, AZ 30

PM2.5 PM10

25

ng m-3

20 15 10 5

to l A ra bi

to l an ni M

os e Tr eh al

e ro s Su c

se lu co G

ce r ly G

Le vo

gl u

co sa

n

ol

0

Fig. 3. Average concentration of saccharide compounds measured in PM2.5 and PM10 from samples collected in Arizona (total number of samples analyzed n = 45 for PM2.5 and n = 46 for PM10).

aerosols in fall instead of spring conincide with the flowering season of the Bauhinia, flower which is locally widespread and starts to bloom in September; and the glucose peak in winter aerosols in Norway possibly was related to fungal spores (Yttri et al., 2007) and other microbially degraded material. As this shows saccharides in aerosols can be used as tracers for the seasonal change of carbohydrate production and utilization in a local ecosystem or regional source trends. 3.3. PM10 vs. PM2.5 in Arizona aerosols Several studies have shown that different saccharide compounds are enriched in different size ranges of the ambient aerosols (Carvalho, Pio, & Santos, 2003; Elbert et al., 2007; Fuzzi et al., 2007; Graham et al., 2003; Pashynska, Vermeylen, Vas, Maenhaut, & Claeys, 2002; Yttri et al., 2007). At the Arizona sampling site, we were able to compare saccharide concentrations in PM2.5 and PM10 samples collected simultaneously, with a goal of using the enrichment of individual saccharide compounds in fine and coarse particulate matter to elucidate local contributing sources. While saccharide compounds were generally measured at higher concentrations in PM10 samples compared to parallel PM2.5 samples (Fig. 3), two distinct patterns in this relationship were observed. Levoglucosan and glycerol had almost equivalent PM10 and PM2.5 concentrations while the remainder of the measured saccharide compounds (glucose, sucrose, trehalose, mannitol, arabitol, sorbitol, erythritol, ribitol and xylitol) had elevated PM10 relative to PM2.5 concentrations. These two different size fractionation patterns indicate that levoglucosan and glycerol predominately are associated with the fine fraction of PM while other saccharide compounds exist in both PM10 and PM2.5. This is consistent with levoglucosan being a tracer for wood smoke (Simoneit et al., 1999), with primary particle emissions in the submicron accumulation aerosol mode (Fuzzi et al., 2007; Kleeman, Schauer, & Cass, 1999; Pio et al., 2008). While the size distribution of aerosol glycerol primary emissions has not been documented before, Graham et al. (2002) reported a high correlation of aerosol glycerol with black carbon (BC), organic carbon (OC) and potassium (K) in particles collected at pasture and primary rainforest sites in Rondônia, Brazil, linking glycerol with combustion sources. Simoneit, Elias et al. (2004) also link some sugar polyols to the emission of particles by thermal stripping during wildfires. The other observed size fractionation shows glucose, sucrose, trehalose, mannitol and arabitol are mainly contributed from PBAPs (Bauer et al., 2008; Bauer, Schueller et al., 2008; Caseiro et al., 2007; Deguillaume et al., 2008; Elbert et al., 2007; Winiwarter et al., 2009), which have been reported to contribute mainly to coarse mode aerosols (Bauer et al., 2008; Cox & Wathes, 1995; Deguillaume et al., 2008; Taylor, Flagan, Valenta, & Glovsky, 2002). This observation is consistent with other ambient measurements conducted elsewhere (Carvalho et al., 2003; Fuzzi et al., 2007; Graham et al., 2003; Pio et al., 2008; Yttri et al., 2007). 3.4. Correlation analysis To further investigate the correlation between saccharide compounds in the observational dataset collected in Texas and Arizona, Pearson's correlation coefficients were calculated based on saccharide concentrations for aerosol samples aggregated by sampling sites, by PM sizes at the Higley site, and the results are summarized in the Appendix. 3.4.1. Correlation of saccharides by sampling site As seasonal variability of aerosol saccharides was found to be similar from samples collected in Texas and Arizona, this relationship was quantified by correlation coefficients between species. For example, concentrations of trehalose and sugar

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polyols including mannitol and arabitol, were highly correlated in PM samples at the four sites, serving as statistical support for a common source for these compounds (Bieleski, 1982; Lewis & Smith, 1967). Glucose was correlated with most sugars and polyols in varying degrees. Since glucose is a fundamental simple sugar in biology, all other sugars and polyols can be considered derivatives in the sense that glucose serves as a primary carbon source for plants and microorganisms (Pigman & Horton, 1980). These correlations, between trehalose and the sugar polyols and between glucose and most other saccharides, have been reported for both aerosol and soil samples (Medeiros, Fernandes, Dick, & Simoneit, 2006; Wan & Yu 2006). No consistent correlation was observed between levoglucosan and the other measured saccharides except for fine particle glycerol, which is consistent with our earlier interpretation that aerosol glycerol may be linked to biomass combustion sources. When comparing the correlation results between sites, it is important to note that the most significant correlations calculated between trehalose and major sugar polyols, were stronger for PM2.5 samples from Clarksville and San Augustine (rural sites) and weaker for data collected at the Dallas site (urban). This may imply that local biogenic sources are less dominant on ambient PM2.5 saccharide concentrations at the urban site compared to the rural site. As the correlation between trehalose and the sugar polyols was stronger in Higley (suburban) than in Dallas (urban) for PM2.5 samples, the impact from the fungal spore derived sources was greater in the desert than the site in Texas. Since the correlation between levoglucosan and glycerol was stronger at Higley and Dallas than at Clarksville and San Augustine, one might speculate that aerosol glycerol in rural sampling locations are more influenced by PBAPs than biomass combustion. Trehalose was found to be highly correlated with sucrose in PM samples collected in Arizona, but this was not observed at the three sites in Texas. Although trehalose resembles sucrose both structurally and functionally as a carrier of energy and carbon (Wiemken, 1990), these two sugars originate differently. Trehalose is widely present in bacteria, fungi, lower plants and invertebrates (Bieleski, 1982), serving as a protectant against stressful environmental conditions (Chaturvedi, Bartiss, & Wong, 1997; Eleutherio et al., 1993; Wong, Murray, Castellanos, & Croen, 1993). Sucrose, on the other hand, is prevalent in the phloem of plants and has been found to be enriched in pollen grains (Bieleski, 1995; Pacini, 2000). The high correlation found between trehalose and sucrose in Arizona aerosols may result from the onset of pollen season concurring with increased microbial metabolism in spring under desert heat and drought condition in Arizona. The dominant pollen types found in Arizona originate from ragweed, mulberry trees, cypress, and mormon tea, all of which have their peak release in March and April (O'Rourke, 1990). March and April also mark the relatively dry season in Arizona, between winter frontal and summer monsoonal rains during which trehalose may be produced as a cell protectant against desiccation for microorganisms. 3.4.2. Correlation of saccharides by particle size In general, the correlation between saccharide compounds was consistent between the PM2.5 and PM10 samples collected at the Higley site. However, all correlations between saccharides were stronger in PM2.5 than PM10 data. Whereas no direct comparison is available in the current literature, results from several studies on the size distribution of aerosol sugars and sugar polyols can be used to elucidate this observation. Yttri et al. (2007) found that the majority of the sugars and the sugar polyols measured at four sites in Norway were predominately in aerosols in the size range 0.25–1.0 m during winter, and in aerosols larger than 2 m in summer. This was attributed to snow on the ground, which effectively reduced resuspension of decaying biogenic material (coarse particles) from the ground in winter. In general, this is in agreement with data of Carvalho et al. (2003), except that the maximum of the aerosol saccharide size distribution varied depending on location. In recognition of these earlier results, the stronger correlations between saccharides in PM2.5 compared to PM10 may have resulted from lower temperatures and atmospheric stagnation that prevented resuspension of PBAPs into the atmosphere. To corroborate this, correlations on the first and second halves of the ambient data were calculated (Appendix). This supplementary analysis showed a greater degree of correlation for PM10 saccharides but a lesser degree of correlation for PM2.5 saccharides in the second half of the data (March–April) than in the first half (January–February). This is likely an effect of increased contribution from saccharides in larger particles during the second half of the sampling period. 3.5. Source isolation of saccharides by positive matrix factorization Positive matrix factorization (PMF) is a powerful statistical tool that can resolve potential sources contributing to ambient particle levels when appropriate source profiles are not available. PMF analyzes sets of ambient aerosol data to estimate the number of sources of particles, the chemical composition of each source, and the amount that each source contributes to each sample, based on the compositional data of aerosols and key representative markers for difference sources. A detailed discussion of the PMF model can be found elsewhere (Paatero, 1997; Paatero and Tapper, 1994). In recognition of the role of saccharides as indicators of biomass burning, PBAPs and other biologically derived carbohydrate from resuspension of soil, dust and associated biota, PMF modeling was performed for ambient data collected in this study, including PM2.5 data from samples collected at the Dallas and San Augustine sites in Texas, and both PM2.5 and PM10 samples collected at the Higley site in Arizona. Ambient concentrations of the major saccharides were used in conjunction with a number of other measured parameters including elemental and organic carbon, ions, particle bound n-alkanes, organic acids, and polycyclic aromatic hydrocarbons. The PMF model developed by EPA (PMF1.1) was used in this study for data analysis and interpretation. A detailed description of EPA PMF1.1 can be found elsewhere (Eberly, 2005). This model has been used extensively for source apportionment of PM based on elemental data and, to a more limited extent, on organic molecular markers (Buzcu, Fraser, Kulkarni, & Chellam, 2003; Jaeckels, Bae, & Schauer, 2007; Ramadan, Song, & Hopke, 2000; Song, Polissar, & Hopke, 2001). In this study, PMF model application

% of species apportioned to factor

80

% of species apportioned to factor

80

% of species apportioned to factor

Y. Jia et al. / Aerosol Science 41 (2010) 62 -- 73

90

69

Dallas PM2.5 - Saccharide rich factor 1

70 60 50 40 30 20 10

SUL

GLY

ERY

ARAB

MANN

LEV

SUC

GLUC

TRE

PINIC

C181

C180

C160

HOP2

HOP1

C31

C30

C29

C28

C27

C26

C25

EC

OC

0

Dallas PM2.5 - Saccharide rich factor 2

70 60 50 40 30 20 10

SUC

MANN

ARAB

ERY

GLY

SUL

SUC

MANN

ARAB

ERY

GLY

SUL

LEV

GLUC

TRE

PINIC

C181

C180

C160

HOP2

HOP1

C31

C30

C29

C28

C27

C26

C25

EC

OC

0

Dallas PM2.5 - Saccharide rich factor 3

80 70 60 50 40 30 20 10 LEV

GLUC

TRE

PINIC

C181

C180

C160

HOP2

HOP1

C31

C30

C29

C28

C27

C26

C25

EC

OC

0

Fig. 4. Three compositional source factors isolated by PMF and characterized by the enrichment of saccharide compounds from analysis of the Dallas PM2.5 samples. Similar profiles were isolated in all model applications (OC: organic carbon; EC: elemental carbon; C25-C31: normal alkane series; HOP1: 17(H), 21(H)-hopane; HOP2: 17(H), 21(H)-29-norhopane; C160: hexadecanoic acid; C180: octadecanoic acid; C181: octadecenoic acid; PINIC: pinic acid; TRE: trehalose; GLUC: glucose; LEV: levoglucosan; SUC: sucrose; MANN: mannitol; ARAB: arabitol; ERY: erythritol; GLY: glycerol; SUL: sulfate).

resolved 7 or 8 source factors that contributed to ambient PM2.5 or PM10 at these three sites, with 3 of the source factors dominated by different saccharide compounds. As an example, shown here in Fig. 4 are the source profiles of three source factors characterized by the enrichment of saccharide compounds, resolved by PMF from data collected in PM2.5 samples from Dallas.

70

Y. Jia et al. / Aerosol Science 41 (2010) 62 -- 73

Table 3 Estimated relative contribution of different sources to ambient PM mass for saccharide-related sources resolved by PMF. Source factor characterized by the enrichment of saccharide compounds

Relative source contribution to PM mass Higley, AZ (%)

San Augustine TX (%)

Dallas, TX (%)

PM2.5 Biomass burning PBAPs and other biologically or microbially derived carbohydrate sources

20 16

22 14

16 5

PM10 Biomass burning PBAPs and other biologically or microbially derived carbohydrate sources

13 21

– –

– –

The first factor is dominated by levoglucosan and glycerol, consistent with this factor representing biomass burning. The second factor is enriched with mannitol and arabitol, and to a lesser extent with trehalose, glucose and erythritol. The third factor enriched with saccharides is dominated by sucrose. The second and third factors are difficult to be convincingly labeled to a unique source, given the possibility of these saccharides coming from either PBAPs or other biologically derived carbohydrate sources such as resuspended soil dust and associated biota (Caseiro et al., 2007; Graham et al., 2003; Simoneit, Elias et al., 2004). However, it is clear that they are of biogenic origin, and the relative source contributions of the saccharide-related sources to the ambient PM mass can be calculated based on the model results using a multiple linear regression between the isolated factor strengths and measured PM2.5 mass (Table 3) (Song et al., 2001). As expected, these saccharide-related sources contributed a higher percentage to the ambient PM2.5 at the rural site (San Augustine) than the urban site (Dallas) in Texas. At the Arizona site, the source impact of biomass burning contributed a greater fraction of PM2.5 compared to PM10 while the PBAPs and other biologically derived sources indicated by the other saccharides contributed more to PM10 than PM2.5. The greater contribution of saccharide-related sources to both PM2.5 and PM10 at the Arizona site compared to Texas sites may be due to the strong influence from diverse flora and fungal species present in the Sonoran desert. 4. Conclusions Ambient PM samples were collected at four sites in Eastern Texas and Central Arizona to characterize the aerosol saccharide compositions and assess the contribution from biomass burning, atmospheric entrainment of soil, and PBAPs in regions with different climate patterns and ecosystems. Measured saccharide concentrations in PM2.5 were much lower at the Arizona site compared to the three Texas sites, but the saccharide content relative to PM2.5 mass and OC was roughly equivalent at the suburban site in Arizona and the urban site in Texas. Samples from the four study sites displayed similar saccharide compositional trends and seasonal variation, with the only exception being trehalose, likely resulting from the influence of local climatic conditions. Comparison with data reported by other studies showed good agreements with a few exceptions that could be interpreted as indicators of ecosystem function, climate, and local aerosol sources. The composition of aerosol samples collected at the Arizona site showed levoglucosan and glycerol were enriched in the fine fraction of the PM while other saccharides including glucose, sucrose, trehalose, and saccharide polyols were more abundant in the coarse fraction PM. This is consistent with the proposed sources of these sugars and knowledge of the size distribution of emissions from these sources. A correlation analysis found a stronger correlation between saccharides in PM2.5 relative to PM10, which may have resulted from lower temperatures and atmospheric stagnations that prevented resuspension of PBAPs into the atmosphere during the sampling period in each study area. Saccharides were also used as markers in a source attribution model that resolved three saccharide-rich source factors, two of which that can be related to primary biologically derived carbon sources. It was estimated that biomass burning contributed significantly to PM2.5 while the PBAPs and other biologically derived sources contributed directly to measured PM10 levels. The estimated contributions from these saccharide-related sources to ambient PM were higher at the rural site than the urban site in Texas, and higher at the Arizona site than the three Texas sites. The above interpretation indicates that saccharides in aerosols can be used as tracers for the seasonal change of carbohydrate production and utilization in a local ecosystem or regional source trends. Acknowledgements We wish to acknowledge both the Texas Commission on Environmental Quality and the Maricopa County (AZ) Department of Air Quality for access to the sampling sites. Funding for this work was provided by the US EPA through the STAR program. Appendix Correlation matrix for the dataset of major saccharide compounds in PM10 and PM2.5 samples collected at the suburban site (Higley) in Arizona, and in PM2.5 samples collected at two rural sites (San Augustine and Clarksville) and one urban site (Dallas) in Texas (n = number of samples used for correlation analysis) (Table A1).

Y. Jia et al. / Aerosol Science 41 (2010) 62 -- 73

71

Table A1 Trehalose

Glucose

Levoglucosan

Sucrose

Sorbitol

Mannitol

Arabitol

Ribitol

Erythritol

Glycerol

Higley, AZ, PM10 (January–April) (n = 46) Trehalose 1 Glucose 0.38 1 Levoglucosan −0.33 0.10 Sucrose 0.82 0.42 Sorbitol −0.05 0.00 Mannitol 0.44 0.25 Arabitol 0.36 0.21 Ribitol 0.02 −0.02 Iso-erythritol −0.07 0.08 Glycerol 0.15 0.20

1 −0.33 0.17 0.01 0.14 −0.14 0.09 0.2

1 −0.22 0.30 0.16 −0.02 −0.14 0.14

1 0.24 0.45 −0.10 0.30 0.26

1 0.77 −0.16 0.03 0.25

1 −0.06 0.39 0.53

1 0.05 −0.06

1 0.53

1

Higley, AZ, PM2.5 (January–April) (n = 45) Trehalose 1 Glucose 0.72 1 Levoglucosan −0.13 0.18 Sucrose 0.84 0.63 Sorbitol – – Mannitol 0.73 0.73 Arabitol 0.62 0.64 Ribitol 0.08 0.11 Iso-Erythritol 0.77 0.62 Glycerol 0.12 0.46

1 −0.23 – 0.19 0.20 −0.18 0.10 0.44

1 – 0.51 0.44 0.24 0.60 −0.06

– –

1 0.84 0.08 0.83 0.49

1 0.25 0.75 0.45

1 0.02 −0.11

1 0.32

1

San Augustine, TX, PM2.5 (November--July) (n = 76) Trehalose 1 Glucose 0.43 1 Levoglucosan −0.08 −0.02 1 Sucrose −0.01 0.35 0.51 Sorbitol 0.63 0.43 0.03 Mannitol 0.82 0.59 −0.24 Arabitol 0.71 0.53 0.07 Ribitol 0.06 −0.10 0.35 Iso-erythritol 0.35 0.46 −0.02 Glycerol −0.06 0.12 0.29

1 0.06 −0.12 0.09 0.11 0.03 0.11

1 0.67 0.75 0.34 0.39 0.08

1 0.88 −0.01 0.57 −0.04

1 0.38 0.66 0.04

1 0.08 0.08

1 0.17

1

Clarksville, TX, PM2.5 (January–July) (n = 40) Trehalose 1 Glucose 0.51 1 Levoglucosan −0.06 0.24 1 Sucrose −0.08 0.38 0.38 Sorbitol 0.64 0.57 0.04 Mannitol 0.78 0.63 −0.03 Arabitol 0.64 0.59 0.03 Ribitol −0.01 −0.28 −0.06 Iso-erythritol 0.60 0.51 0.11 Glycerol −0.02 0.28 0.26

1 0.02 0.06 0.05 −0.11 −0.07 0.00

1 0.78 0.90 0.21 0.63 0.14

1 0.85 −0.18 0.71 0.06

1 0.24 0.71 0.23

1 −0.14 0.05

1 0.19

1

Dallas, TX, PM2.5 (January–July) (n = 57) Trehalose 1 Glucose 0.60 1 Levoglucosan 0.07 0.20 Sucrose 0.22 0.50 Sorbitol 0.58 0.63 Mannitol 0.35 0.35 Arabitol 0.49 0.57 Ribitol 0.00 0.08 Iso-erythritol 0.08 0.21 Glycerol 0.04 0.12

1 0.24 −0.03 −0.07 0.12 0.15 0.51

1 0.50 0.66 0.02 0.20 0.15

1 0.64 −0.20 0.00 −0.23

1 −0.09 0.26 −0.11

1 0.27 0.31

1 0.25

1

1 – 0.69 0.58 – 0.81 0.00

1 – – – – –

1 0.83 – 0.85 0.26

1 – 0.79 0.25

1 – –

1 0.16

1

1 0.48 0.00 −0.31 −0.21 0.33 0.34 0.53

Higley, AZ, PM2.5 (January–February) (n = 22) Trehalose 1 Glucose 0.79 1 1 Levoglucosan −0.25 −0.01 Sucrose 0.94 0.72 −0.22 Sorbitol – – – Mannitol 0.81 0.64 −0.15 Arabitol 0.71 0.62 −0.16 Ribitol – – – Iso-erythritol 0.88 0.64 −0.10 Glycerol 0.08 0.32 0.27 Higley, AZ, PM2.5 (March–April) (n = 23) Trehalose 1 Glucose 0.69 1

1 – –

72

Y. Jia et al. / Aerosol Science 41 (2010) 62 -- 73

Table A1 Cont.. Trehalose

Glucose

Levoglucosan

Sucrose

Sorbitol

Mannitol

Arabitol

Ribitol

Erythritol

Glycerol

0.37 0.70 – 0.74 0.58 – 0.50 0.39

0.23 0.66 – 0.88 0.59 – 0.77 0.60

1 0.01 – 0.46 0.52 – 0.16 0.65

1 – 0.52 0.53 – 0.51 0.12

1 – – – – –

1 0.78 – 0.82 0.71

1 – 0.68 0.46

1 – –

1 0.50

1

Higley, AZ, PM10 (January–February) (n = 22) Trehalose 1 Glucose 0.37 1 Levoglucosan −0.13 0.20 1 Sucrose 0.79 0.21 −0.22 Sorbitol – – – Mannitol 0.52 −0.01 −0.07 Arabitol 0.53 0.03 0.07 Ribitol – – – Iso-erythritol 0.18 0.41 0.56 Glycerol −0.01 −0.09 0.28

1 – 0.23 0.15 – −0.14 −0.08

1 – – – – –

1 0.80 − 0.38 0.13

1 − 0.65 0.42

1 – –

1 0.40

1

Higley, AZ, PM10 (March–April) (n = 23) Trehalose 1 Glucose 0.51 1 Levoglucosan 0.29 0.15 Sucrose 0.71 0.69 Sorbitol – – Mannitol 0.72 0.60 Arabitol 0.56 0.43 Ribitol – – Iso-erythritol −0.28 −0.05 Glycerol 0.19 0.42

1 – 0.61 0.33 – −0.32 0.16

1 – – – – –

1 0.73 – −0.10 0.37

1 – 0.38 0.65

1 – –

1 0.59

1

Levoglucosan Sucrose Sorbitol Mannitol Arabitol Ribitol Iso-erythritol Glycerol

1 0.20 – 0.30 0.50 – 0.02 0.52

Level of significance  = 0.05 (two-tailed test).

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