Model simulation of NO3, N2O5 and ClNO2 at a rural site in Beijing during CAREBeijing-2006

Atmospheric Research 196 (2017) 97–107

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Model simulation of NO3, N2O5 and ClNO2 at a rural site in Beijing during CAREBeijing-2006

MARK

Haichao Wanga, Keding Lua,⁎, Zhaofeng Tana, Kang Sunb, Xin Lia, Min Hua, Min Shaoa, Limin Zenga, Tong Zhua, Yuanhang Zhanga,c a b c

State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China China National Environmental Monitoring Centre, Beijing, China CAS Center for Excellence in Regional Atmospheric Environment, Chinese Academy of Science, Xiamen, China

A B S T R A C T A chemical box model was used to study nitrate radical (NO3), dinitrogen pentoxide (N2O5) and nitryl chloride (ClNO2) in a rural site during the Campaign of Air Quality Research in Beijing 2006 (CAREBeijing-2006). The model was based on regional atmospheric chemistry mechanism version 2 (RACM2) with the heterogeneous uptake of N2O5 and the simplified chloride radical (Cl) chemistry mechanism. A high production rate of NO3 with a mean value of 0.8 ppbv/h and low mixing ratios of NO3 and N2O5 (peak values of 17 pptv and 480 pptv, respectively) existed in this site. Budget analysis showed that NO emission suppressed the NO3 chemistry at the surface layer, the reaction of NO3 with VOCs made a similar contribution to NO3 loss as N2O5 heterogeneous uptake. The NO3 chemistry was predominantly controlled by isoprene, and NO3 oxidation produced organic nitrate with a mean value of 0.06 ppbv/h during nighttime. The organic nitrate production initiated by NO3 was equal to that initiated by OH, implying the importance of nighttime chemistry for secondary organic aerosol (SOA) formation. We confirmed that the N2O5 heterogeneous reaction accounted for nighttime particle NO3− enhancement, with a large day to day variability, and made less of a contribution to NOx loss compared to that of OH reacting with NO2. Additionally, abundant ClNO2, up to 5.0 ppbv, was formed by N2O5 heterogeneous uptake. ClNO2 was sustained at a high level until noon in spite of the gradually increasing photolysis of ClNO2 after sunrise. Chlorine activation caused by N2O5 heterogeneous uptake increased primary ROx formation by 5% and accounted for 8% of the net ozone production enhancement in the morning.

1. Introduction Nitrate radical (NO3), produced by the reacting NO2 with O3 (R1), has a noticeable oxidation initiation capability in nocturnal chemistry when OH and O3 are limited (Wayne et al., 1991; Tsai et al., 2014). NO3 plays a key role in removing pollutants, such as volatile organic compounds (VOCs) and NOx, during the nighttime. For some VOCs (especially some biogenic hydrocarbons), NO3 dominates the initial oxidation with a rapid reacting rate (McLaren et al., 2004; Geyer et al., 2001; Brown et al., 2009) and produces organic nitrate at an effective yield (R2), which is an important precursor for forming secondary organic aerosols (SOA) (Atkinson and Arey, 2003; Ng et al., 2008; Brown and Stutz, 2012). A recent study has shown that NO3 chemistry is responsible for the effective submicron aerosol nitrates in Europe (Kiendler-Scharr et al., 2016). For some special amines emitted by fossil fuel combustion power plants equipped with carbon capture and storage (CCS), NO3 oxidation can provide an important removal route at ⁎

Corresponding author. E-mail address: [email protected] (K. Lu).

http://dx.doi.org/10.1016/j.atmosres.2017.06.013 Received 28 March 2017; Received in revised form 11 June 2017; Accepted 13 June 2017 Available online 15 June 2017 0169-8095/ © 2017 Published by Elsevier B.V.

nighttime (Weller and Herrmann, 2015). In the surface layer of an urban site, continuously emitted NO by anthropogenic activities is an important NO3 sink pathway via a rapid Reaction (R3) and suppresses the NO3 chemistry, but in a rural region far from the urban environment, this reaction is not important (Geyer et al., 2001; Stutz et al., 2010; Khan et al., 2015).

NO2 + O3 → NO3 + O2

(R1)

NO3 + R1 − C═C − R2 → R1 − C─C(NO3) − R2

(R2)

NO3 + NO → 2NO2

(R3)

NO2 + NO3 + M → N2 O5 + M

(R4)

N2 O5 → NO2 + NO3

(R5)

N2O5 is formed by the reaction of NO2 with NO3 and is easily thermally decomposed with a strong temperature dependent

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Fig. 1. The map of Yufa site of the campaign CAREBeijing2006. The black circle represents the center of Beijing city and the red drop represents the location of Yufa site. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

et al., 2012). Many studies have shown that hundreds of pptv to ppbv of ClNO2 lead to the enhancement of several ppbv of ozone production (Osthoff et al., 2008; McLaren et al., 2004; Riedel et al., 2014; Sarwar et al., 2014; Tham et al., 2016) and account for 10–30% of primary ROx production under high ClNO2 (Tham et al., 2016).

equilibrium (Wangberg et al., 1997) that is based on the exchange between NO3 and N2O5 (R4, R5). N2O5 chemistry has a significant indirect impact on NO3 chemistry and even controls NO3 loss under some conditions (Dentener and Crutzen, 1993; Aldener et al., 2006). Its heterogeneous hydrolysis is one of the major processes responsible for atmospheric NOx loss (Geyer and Stutz, 2004; Tsai et al., 2014) and prominently contributes to nighttime nitrate enhancement (Pathak et al., 2011; Shon et al., 2013), which also impacts the chloride cycle by the subsequent production of ClNO2 (R6) (Osthoff et al., 2008; Thornton et al., 2010). The loss rate of N2O5 on a particle surface can be briefly described by Eq.1, where c is the mean molecule speed of N2O5, Sa is the aerosol surface area density and γ is the uptake coefficient of N2O5.

N2 O5 + (H2 O Or Cl−) → (2 − Φ) NO3− + Φ Clno2

kN2O5 = c∙γ∙Sa 4

ClNO2 + hν(λ < 852 nm) → Cl + NO2

(R7)

China has suffered from heavy air pollution along with the high speed of economic development in the past few decades, especially in the North China Plain (NCP), Pearl River Delta (PRD) and Yangtze River Delta (YRD) (Richter et al., 2005; Huang et al., 2014; Liu et al., 2016). Previous studies have found a high mixing ratio of NO3 in Shanghai (Wang et al., 2013), as well as high mixing ratios of N2O5 and ClNO2 in Hong Kong (Tham et al., 2014; T. Wang et al., 2016; Brown et al., 2016) and NCP (Tham et al., 2016). These observations and the regional model revealed that the heterogeneous uptake of N2O5 and chlorine activation had a significant effect on daytime O3 and ROX chemistry (Xue et al., 2015; Li et al., 2016). However, systematical studies on NO3, N2O5, ClNO2 and relevant species in the field are rarely conducted in China. In this study, we used a box model based on RACM2 with a simplified N2O5 heterogeneous uptake and Cl chemistry mechanism to study the chemical processes of NO3, N2O5 and ClNO2 in Beijing during the Campaign of Air Quality Research in Beijing 2006 (CAREBeijing2006) (Wu et al., 2011), and to obtain insights into the effects of NO3N2O5 on nighttime chemistry as well as subsequent chloride activation in daytime chemistry. We also evaluated the impact of NOx removal, nighttime nitrate enhancement, ROx abundance and the net ozone production rate.

(R6) (1)

N2O5 hydrolysis uptake is one of the main uncertainty sources of the NO3 budget due to the N2O5 uptake coefficient being highly variable and difficult to quantify (Brown and Stutz, 2012; Wang and Lu, 2016). Many laboratory and field measurement studies have reported that the N2O5 uptake coefficient is ranged from lower than 0.001 to 0.1, and is effected by various factors, such as the temperature, RH, particle's physical characteristics (particle phase, mixing status and particle size) and composition (liquid water content, Cl−, SO42 −, NO3−) (Wahner et al., 1998; Mentel et al., 1999; Kane et al., 2001; Hallquist et al., 2003; Thornton et al., 2003; Thornton and Abbatt, 2005; Brown et al., 2006; Brown et al., 2009; Bertram and Thornton, 2009; Riedel et al., 2012; Wagner et al., 2013; Morgan et al., 2015; Phillips et al., 2016), but details on the comprehensive influence of these impact factors are still unclear. ClNO2 produced by N2O5 hydrolysis on Cl− containing particles and has a negligible sink during the night. Many studies have observed ppbv levels of ClNO2 in marine and inland regions (Osthoff et al., 2008; Thornton et al., 2010; Phillips et al., 2012; Riedel et al., 2012; Riedel et al., 2014; Mielke et al., 2016; Tham et al., 2014; T. Wang et al., 2016; Tham et al., 2016). ClNO2 has been proposed to be a dominated Cl· source by a photolyzing reaction, and liberate chlorine radical (Cl) and NO2 after sunrise (R7). The released Cl oxidizes VOCs rapidly and produces peroxyl radicals, which subsequently react with NO to generate NO2 and enhance ozone production (Simon et al., 2009; Sarwar

2. Methodology 2.1. Field campaign site This campaign took place at the Yufa site (see Fig. 1) in the vicinity of Beijing as a part of the Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing 2006) from 11 August to 9 September 2006. The Yufa site is a typical rural site (39°31′N, 116°18′E) and is located approximately 45 km south of Beijing. Some local emission sources were located around the site, including several factories and a highway running from the south to the north. HOx, O3, 98

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Table 1 Critical measurements of trace gas and aerosols in Yufa site during CAREBeijing-2006. Species

Techniques

Detection of limit (1σ)

Accuracy

References

OH NO NO2 O3 CO HONO Photolysis rates C3-C12 VOCs PNSD Aerosol ionic composition

LIFa CLb CLb UV photometry IR photometry LOPAPc Spectra radiometer GC-FID/PIDd SMPS + APS GAC

6 × 105 cm− 3 (5 min) 25 pptv (5 min) 80 pptv (5 min) 0.5 ppbv (5 min) 4 ppbv (5 min) 7 pptv (5 min) Varies with species 1–90 pptv (30 min) 3.4 nm-20 μm (10 min) 0.01–0.16 μg m− 3 (30 min)

± 20% ± 7% ± 13% ± 5% ± 5% ± 10% ± 10% ± 10% ± 30% ± 10%

Lu et al., 2013 Lu et al., 2013 Lu et al., 2013 Lu et al., 2013 Lu et al., 2013 Li et al., 2012 Lu et al., 2013 Yuan et al., 2009 Yue et al., 2009 Dong et al., 2012

a b c d

Laser Induced Fluorescence. Chemiluminescence. LOng-Path Absorption Photometry. Gas Chromatography Flame-Ionization Detector/Photo-Ionization Detector.

NOx, CO, C3-C12 VOCs, HONO, photolysis frequencies and meteorological parameters (temperature, pressure, relative humidity, wind direction and wind speed) were measured, and the details can be found in Lu et al. (2013) and Lu et al. (2014). Aerosol measurement include particle number size distribution (PNSD) and the particle ionic composition were also available during this campaign, the details of the relevant parameters and instruments used in the following analysis were listed in Table 1. The sample inlets were mounted on the roof of a building approximately 12 m above the ground. Nighttime was defined as when the solar zenith angle was larger than 90°, and the sunrise and sunset times were at 05:42 and 18:52 CNST (CNST: Chinese National Standard Time; i.e., UTC + 8 h), respectively. The typical meteorological conditions were a high temperature (average of 24.6 °C), high relative humidity (average of 71%) and low wind speed (average of 1.7 m/s) with the main wind direction from the south (Garland et al., 2009).

Table 2 Measured hydrocarbons and their assignment to RACM2 species during CAREBeijing2006. RACM2 ETH HC3 HC5

HC8

ETE BEN DIEN OLI OLT ISO TOL XYM

2.2. Model description XYO

A zero-dimensional chemical box model constrained by the field campaign data was applied to simulate the diurnal cycle of NO3, N2O5 and ClNO2. The box model was based on the Regional Atmospheric Chemical Mechanism version 2 (RACM2) described in Goliff et al. (2013), and N2O5 heterogeneous hydrolysis (R6) and a simplified chloride chemical mechanism were added. The uptake coefficient of N2O5 and production yields of ClNO2 and NO3− from N2O5 heterogeneous hydrolysis were parameterized as γ(N2O5), ϕ(ClNO2) and 2 −ϕ (ClNO2), respectively. j(ClNO2) was calculated according to the NASAJPL recommendation based on the work by Ghosh et al. (2012). Chloride chemistry was adapted to RACM2 from MCM (Xue et al., 2015), and the oxidation products from reactions between lumped VOC species and chloride radicals were adapted from those of OH oxidation from RACM2. For the reaction rate constant of the lumped species with Cl, the fastest value from different species was used to represent the upper limit of the impact of chloride chemistry. Additionally, the mechanism was updated with an explicit isoprene oxidation process from recent studies (Crounse et al., 2011; Peeters et al., 2014), which had been used in a field campaign in a rural site of North China Plain (Tan et al., 2017). The details of the N2O5 uptake and chlorine reactions mechanisms mentioned above can found in the supplement information (Table S1). The model runs were constrained by O3, HONO, NO, NO2, CO, VOCs (VOC species and assignment to RACM2 were listed in Table 2), photolysis frequencies, ambient temperature, pressure, and the aerosol surface area (Sa), γ(N2O5) (parameterized) and ϕ(ClNO2) (parameterized). The aerosol surface area was calculated based on the particle size distribution measured by a thermal decomposition mobility particle sizer (TDMPS 3091, TSI, Inc.) and an aerodynamic particle sizer

Measured hydrocarbons ethane propane, n-butane, i-butane, 2,2-dimethylbutane i-pentane, n-pentane, cyclopentane, n-hexane, 2,3-dimethylbutane, 2methylpentane, 3-methylpentane, n-heptane, 2,4-dimethylpentane, 2,3-dimethylpentane, methylcyclopentane, 2-methylhexane, MTBE cyclohexane, 3-methylhexane, 2,2,4-trimethylpentane, 2,3,4trimethylpentane, n-heptane, methylcyclohexane, 2-methylheptane, 3methylheptane, n-octane, n-nonane, n-decane ethene benzene 1,3-butadiene cis-butene, trans-2-pentene, cis-2-pentene propene,1-butene, i-butene, 1-pentene, 1-hexene, styrene isoprene toluene, ethylbenzene, i-propylbenzene, n-propylbenzene m-ethyltoluene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene, m-diethylbenzene o-xylene, o-ethyltoluene

(APS 3321, TSI, Inc.). The particles were assumed to be spherical, and the size used in the calculation was from 3.4 nm to 2.5 μm. The hygroscopic growth was corrected by the hygroscopic factor parameterized with RH (Liu et al., 2013). The model runs were from 22 August to 1 September 2006 so that most of the data were accounted for. The lifetime of the model-generated species was set to 24 h with respect to the dry deposition. The lifetime corresponds to an assumed deposition velocity of 1.2 cm/s in a well-mixed boundary layer of 1000 m. The input data were averaged and interpolated to 5 min of resolution if the original resolution time was shorter or longer than 5 min. Previous works showed that the presence of the particle organic content may reduce the uptake coefficient of N2O5 when the organic film formed and covered on the surface of the inorganic core (Thornton and Abbatt, 2005; McNeill et al., 2006; Anttila et al., 2006). But the suppression degree will depend on the amount, species (Cosman and Bertram, 2008a; Cosman et al., 2008b; Knopf et al., 2007; Griffiths et al., 2009; Knopf et al., 2011), and recently reported the oxidation state of the organics with the solubility and viscosity (Gaston et al., 2014; Grzinic et al., 2015). In this site, the organic content mass was the most important part in PM1 by accounting for ~40% in the evening (Takegawa et al., 2009), although the elemental composition and the oxygen to carbon atomic ratio (O:C) was unavailable, the subsequent measurement in Beijing showed the O:C < 0.4 in the evening (Wu et al., 2017), implied that organic suppression may pronounced although the organic coatings not always exist in nature and coat all aerosol. 99

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particulate nitrate, chloride and liquid water contents were given by (Eq. 5)

Here we assumed that all the particles were hydrophobic and organic coated on the inorganic aqueous core. The net uptake coefficient of N2O5 was given by an extended resister model (Eq.2), which considered the dependence of γ(N2O5) on the inorganic core uptake coefficient (γcore) and organic coating uptake coefficient(γcoating). And assumed the inorganic core are internally mixed and the aerosol composition distribution is the same with the variation of particle size

1 1 1 = + γ (N2 O5 ) γcore γcoating

−1

[H2 O] ⎞ ϕ(ClNO2) = ⎛1 + 50[Cl−] ⎠ ⎝ ⎜

(2)

4RTHorg Dorg R c cmean lRp

(3)

where Horg and Dorg are the solubility and diffusivity, respectively, of N2O5 in an organic coating with a thickness of l. Rc and Rp are the radii of the aqueous core and particle, respectively. Over the entirety of a model run, the uptake coefficient of the organic coating (γcoating) was held constant at 0.01, which represented a typical value corresponding to the radius of particle of 300 nm with the average RH of 85% at 298 k encountered during the model run time at night. The thickness of the organic coating was 5 nm, HorgDorg was set to 0.03 × HaqDaq as derived by Anttila et al. (2006) with Haq = 5 mol L− 1 atm− 1 and Daq = 10− 9 m2 s− 1. For the inorganic core, uptake coefficient parameterization was based on the theory framework (R8–R11) from Bertram and Thornton (2009) and given by (Eq. 4).

N2 O5 (g) ⇌ N2 O5 (aq)

N2 O5 (aq) + H2 O(l) ⇌ H2 ONO2 (aq) + NO3− (aq) H2 ONO2 (aq) + H2 O(l) → H3

O+

(aq) + HNO3 (aq)

3. Result and discussion

(R8)

3.1. Overview of the modeling results and related species

(R9)

Fig. 2 presents the time series of the modeling results and related species, including the measured NO, NO2, O3, aerosol surface area (Sa) and the production rate of NO3 (P(NO3)) by the reaction of NO2 + O3; parameterization of γ(N2O5); and modeling results of NO3, N2O5, and ClNO2. As the key precursor of NO3, NO2 was range from 1.5 ppbv to 66.0 ppbv, with a mean value of 14.0 ± 8.0 ppbv. O3 was range from the limit of instrument detection, that is, 0.5 ppbv, to a maximum of 101.0 ppbv, with a mean value of 25.1 ± 7.0 ppbv. The elevated NO2 and O3 ensured high production of NO3 and N2O5 with the maximum of production rate of NO3 over 4.5 ppbv/h. The peak nighttime concentrations of NO3 and N2O5 showed highly variability from day to day, that is, 5–17 pptv and 30–480 pptv, respectively. The relatively low mixing ratio during most of the days indicated that the existing strong loss paths of NO3 or N2O5. The NO mixing ratio at this site during the nighttime was generally small and below the instrument detection limit (0.2 ppbv), but sometimes, shape peaks were found by occasional anthropogenic emissions from the city or from the industrialized regions in the south of Beijing (Lu et al., 2013; Lu et al., 2014; Garland et al., 2009), which consumed NO3 rapidly and had a significant effect on the mixing ratio of NO3 and N2O5. Fig. 3(a) shows the distinct diurnal profiles of NO3 and N2O5. NO3 began to accumulate near the sunset and reached a peak rapidly in a few hours. The peak occurred at approximately 19:30 and then decreased to low values at sunrise. N2O5 had a similar variation tendency as NO3, but the peak of N2O5 occurred later than that of NO3 (approximately 2 h) and the mixing ratio was approximately one order of magnitude larger than that of NO3. The mean values of NO3 and N2O5 at nighttime were 3.9 pptv and 38.0 pptv, respectively. However, Sa was elevated to have a mean value of 3 × 103 μm2/cm3, and the peaks of the ClNO2 mixing ratios ranged from 0.2 ppbv to 5.0 ppbv, with high day to day variability, which was comparable to the observed results in the semi-rural site of NCP (Tham et al., 2016). The maximum concentration occurred on 24 August along with the highest NO3 and N2O5 contents, when the high production rate of NO3 (mean value of 1.8 ppbv/h) and negligible NO occurred simultaneously. Fig. 3(b) shows that the mixing ratio of Cl− particles was approximately fourfold higher than that of ClNO2 and had a similar trend in its diurnal profile. The mixing ratio of Cl− was comparable

(R10)

H2 ONO2 (aq) + Cl− (aq) → ClNO2 + H2 O (l)

(R11) −1

k [H O (l)] k [Cl−] ⎞ ⎞ ⎛ γcore = Ak 9f ⎜1 − ⎛⎜1 + 10 2 − + 11 ⎟ k 9b [NO3 ] k 9b [NO3−] ⎠ ⎟ ⎝ ⎝ ⎠

(5)

The predicted ϕ of ClNO2 varied from 0.4 to 1.0, with an average value of 0.74, which was comparable to the other estimated results (Mielke et al., 2013; Tsai et al., 2014). Additionally, we found that the rate constants of the alkenes with the double bond elsewhere in the molecule (OLI) with NO3 applied in RACM2 were 3.91 × 10− 12 molecules cm− 3 s− 1 at 298 K, but in fact, only three OLI species were measured in this campaign, included cis-2butene, cis-2-pentene, and trans-2-pentene. Cis-2-Pentene is the most reactive species towards NO3, with a rate constant of 3.8 × 10− 13 molecules cm− 3 s− 1 at 298 K adopted from IUPAC (International Union of Pure and Applied Chemistry) website (Atkinson et al., 2004, 2006), therefore, we replaced the rate constant of OLI with NO3, which had an upper constant value and a more constrained rate constant of 3.8 × 10− 13 molecules cm− 3 s− 1 in the model. The difference between the NO3 loss frequency calculated based on RACM2 and the sum of the single NO3 loss frequency of the measured VOCs was determined, and the results of RACM2 were slightly higher, with a bias of approximately 20%.

For the organic coating, the uptake coefficient is given by (Eq.3)

γcoating =

⎟

(4)

where A is an empirical parameter based on the laboratory studies of the inorganic aerosol, and the particulate nitrate, chloride and liquid water contents were considered in the parameterization. The mixing ratio of particulate nitrate and chloride ions measured by the gas and aerosol collector system (GAC) (Dong et al., 2012). The liquid water content was calculated by assuming that the volume of liquid water content is equal to the difference of that before and after hygroscopic growth correction, and neglecting the difference of density between dry and ambient particles, the details of the liquid water content calculation can see the supplement information (Section 1). The time series of the parameterization of N2O5 uptake coefficients and ClNO2 yield and relevant parameters (include the particle chloride, nitrate and the calculated liquid water content) were plotted in the supplement (Fig. S1). The parameterized γcore was range from < 0.001 to 0.03 and within the range of previous lab and field studies. After considering the organic coating the γ(N2O5) decreased and varied from 0.002 to 0.01, with an average value of 0.007 at nighttime, which was in the range (0.001–0.03) reported by some field measurements results (Brown et al., 2006; Morgan et al., 2015; Riedel et al., 2012; Phillips et al., 2016). The parameterized γ(N2O5)∙ϕ(ClNO2) reflected the ClNO2 formation capacity to some extent, which clearly had a diurnal profile, with maximum values in the early morning and minimum values at noon, but the values of γ(N2O5)∙ϕ(ClNO2) were relatively low, with a mean value of 0.006. To test the impacts of ClNO2 chemistry on the photochemical process of the next morning, two types of yield ϕ(ClNO2) were tested in the model. The first was by setting the yield to zero to represent the absence of ClNO2 chemistry, and the second was using parameterization data following the recommendation of Mielke et al. (2013), where the 100

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Fig. 2. Time series of measured NO, NO2, O3, Sa, P(NO3) and parameterized γ(N2O5)ϕ (ClNO2), j(ClNO2) and modeled NO3, N2O5, ClNO2.

with that in Guangzhou (5.3 ppbv in average in winter in 2007/2008), China, and the pronounced ClNO2 was observed in its outflow in Hong Kong (T. Wang et al., 2016). We noticed that the similar mean diurnal variation was happened in CAREBeijing-2014 at Wangdu site (Ye et al., 2016; Tham et al., 2016). According to Tham et al., 2016, coal fired power plants may be a dominant source of chloride in the region, and the chlorine in the coal in the form of HCl gas can then be transformed into the aerosol phase. Ye et al. (2016) showed the mean diurnal profiles of HCl gas has inverse tendency with particle Cl− in Wangdu site, implied the acid displacement may have happened during the day. ClNO2 began to accumulate continuously after sunset by N2O5 heterogeneously reacting on the aerosol surface, and it peaked in the early morning at approximately 6:00 until sunrise. The high mixing ratio of ClNO2 persisted until noon, even when the photolysis rate was larger than 0.0001 s− 1, which indicated that the release of Cl radicals by ClNO2 photolysis had a lasting effect on the first half of daytime photochemistry. To analysis the implications caused by the uncertainties of the parameterization, sensitivity tests were done by three extreme model cases (M0–M3), the definition were listed in Table 3, as shown in Fig. 4, double γ (M2) or without organic coating (M1) resulted in lower mixing ratios of NO3, N2O5 and higher ClNO2, and half γ (M3) resulted in the inverse effects. It is predictable because of higher uptake coefficients increasing the loss of NO3 and N2O5 and promoting the production of ClNO2. But the corresponding variation of NO3 and N2O5 concentration

Table 3 Description of the sensitivity tests with the variation of N2O5 uptake coefficients. Name

Description of the parameterization

M0 M1 M2 M3

γ, with core and organic coating γcore, with core only (without organic coating) 2γ, double values of the gamma used in M0 0.5γ, half values of the gamma used in M0

were much smaller (within 30%) that those of the N2O5 uptake coefficients, these are mostly because of the loss of NO3 and N2O5 loss were controlled by other factors (specifically NO, cf. Fig. 5) so that the mixing ratios of NO3 and N2O5 were not so sensitive with the change of N2O5 uptake coefficients. Since the N2O5 uptake is the only formation path of ClNO2 in the model set, so the modeled mixing ratio of ClNO2 is much sensitive to the change of N2O5 uptake coefficient than that of NO3 and N2O5.

3.2. Budget of NO3-N2O5 To understand the details of the sources and sinks of nocturnal NO3 and N2O5 chemistry in Beijing, we performed a budget analysis of NO3N2O5. Due to the fast exchange between NO3 and N2O5, the two species were regarded to be one target species and the reciprocal reaction Fig. 3. The mean diurnal profiles of (a) NO3 (orange), N2O5 (red); (b) ClNO2 (navy) and Cl− from aerosol (teal). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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site (as shown by the pie chart on the left of Fig. 5 (b)), but the net reaction production was the precursor NO2 and did not remove NOx from the atmosphere. Despite of the reaction of NO + NO3, the reaction of NO3 with VOCs dominated the first half of night by accounting to 69% of the NO3 loss, and N2O5 heterogeneous uptake dominated the second half of night by accounting to 66% of the NO3 loss, but the total contribution to the loss of NO3 and N2O5 was nearly the same.

τss (NO3) =

[NO3 ] k1 [NO2 ][O3 ]

(6)

The steady-state lifetime of NO3 can estimated through the mixing ratios of NO3, NO2 and O3, as described in Eq. (6), where k1 is the rate constant for R1. This method was used to assess the heterogeneous hydrolysis of N2O5 and estimate the uptake coefficients (Brown et al., 2003; Brown et al., 2006; Brown et al., 2009; Crowley et al., 2010; Sobanski et al., 2016; Brown et al., 2016; Phillips et al., 2016). In this campaign, the lifetime was lower than 45 s in the nighttime with a mean value of 20 s, indicated the NO3 loss is rapid. Previous studies showed that NO3, N2O5 and ClNO2 concentrations will likely to be larger in the higher altitude due to the removal of surface emitted NO by the O3 from aloft (Brown et al., 2007a; Brown et al., 2007b; Young et al., 2012; Tham et al., 2016). Lower NO concentration at higher altitude would also mean smaller loss rate and longer lifetime of NO3 and N2O5 in the upper layer in Beijing. Fig. 4. Sensitivity tests of the N2O5 uptake coefficients to the modeled mixing ratios of NO3, N2O5 and ClNO2.

3.3. NO3 loss frequency by hydrocarbons

between them was ignored. Fig. 5 plots the mean diurnal variation budget of NO3-N2O5. The reaction of NO2 with O3 was a major part of P (NO3); other sources, such as the reaction of HNO3 with OH, were negligible. The nighttime maximum of P(NO3) occurred a few hours after sunset due to high NO2 and O3 and then decreased along with the removal of NO2 and O3. The daily peaks of the nighttime production rate were highly variable day to day, from lower than 1.0 ppbv to 4.5 ppbv, and the average value was 0.8 ppbv/h. NO3 is photochemically unstable with considerable photolysis frequencies, and the lifetime of NO3 in the daytime is lower than 5 s (Wayne et al., 1991). In parallel, the high mixing ratio of NO emissions also accounted for the daytime NO3 and N2O5 losses, and the above loss processes led to insignificant NO3 and N2O5 in daytime chemistry; during the nighttime, the reaction between NO3 and NO contributed to 59% of the NO3-N2O5 loss at this

Fig. 6 shows the calculation of the hydrocarbon reaction from the NO3 loss frequency based on RACM2. Isoprene dominated NO3 loss, with a contribution of 50%, followed by the double bond at the end or terminal position of the molecule (OLT). These two compounds were responsible for more than 95% of the NO3 loss frequency. The OLT contribution remained stable throughout the night, and isoprene commonly came from biogenic emissions during the daytime and began to decrease persistently after sunset. The average value of the NO3 loss frequency caused by hydrocarbons was 0.011 s− 1, but this value may represent the lower limit of the NO3 loss frequency of hydrocarbons because several hydrocarbons like terpenes were not measured during this campaign, which are important organic reactants that interact with NO3 in some forest regions. To assess the implication of the absence input of monoterpene in the model, we did an sensitivity test by adding 41 pptv API (represent the sum of α-pinene and β-pinene in model) into Fig. 5. Production (a) and destruction rate (b) of NO3, N2O5 calculated by RACM2. Panel (a): breakdown of the production of NO3 from the reaction of NO2 with O3 and HNO3 react with OH; Panel (b): breakdown of the loss rate of NO3 and N2O5, the peak filled denoted the NO3 photolysis in the daytime, the green, red and grey filled part is the loss rate by NO3 + VOC, N2O5 uptake reaction and NO3 + NO, respectively. The pie chart shows the nighttime NO3 and N2O5 loss proportion by the same colors. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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3.4. Nighttime nitrate enhancement by N2O5 heterogeneous uptake Previous studies have shown that a high concentration of nitric acid was found in particles in Beijing and other megacities and suggested the nighttime NO3− enhancement events were predominantly attributed to N2O5 hydrolysis (50%–100%) (Pathak et al., 2009; Pathak et al., 2011). In this campaign, nighttime NO3− enhancement events were observed during five nights by the GAC instrument, but the contribution from N2O5 heterogeneous uptake was found to be highly variable day to day from 7%–100%. Fig. 8(a) shows that the NO3− enhancement event occurred from 19:30 on 23 August to 00:30 on 24 August, with the mixing ratio of NO3− explosively increasing from 10 μg/m3 to 23 μg/ m3. At least 13 μg/m3 NO3− was needed to meet the observations from the 5 h, assuming that the formation of NO3− via the net uptake of HNO3 to aerosol can be ignored. The integral production from N2O5 hydrolysis uptake with an offset of 10 μg/m3 had a good performance in simulating the tendency and quantity of the NO3− increase. The NO3− formed by N2O5 hydrolysis was calculated to be 20.0 μg/m3 and had the ability to support particle nitrate enhancement, which was comparable to the results of Pathak et al. (2011) and Wagner et al. (2013), illustrating the significance of N2O5 heterogeneous uptake in nighttime nitrate formation. Fig. 8(b) shows another nitrate enhancement that occurred at 19:30 on 24 August to 25 August. This condition was similar to the case on the night of 23 August. NO3− increased from 6 μg/ m3 to 23 μg/m3 in 8 h, but the contribution from N2O5 heterogeneous uptake was only approximately 1.2 μg/m3 and accounted for 7% of the total nighttime NO3− enhancement at most. This meant that other mechanisms, e.g., partitioning of HNO3 to the aqueous phase, may have been responsible for the nighttime nitrate enhancement.

Fig. 6. The calculation of NO3 loss frequency by hydrocarbons during the nighttime based on the RACM2, included the double bond elsewhere in the molecule (OLI), the double bond at the end or terminal position of the molecule (OLT), isoprene and other hydrocarbons (e.g. formaldehyde).

a test model, the API input value was based on an average result of the sequence observation (canister sampling), here we named this test model as MAPI, since the input of API lead to higher NO3 loss rate and affected the sequence reactions, the mixing ratio of NO3, N2O5 and ClNO2 were decreased (as shown in Fig. S2), but the influence is small (decreased ~ 10% for the three species). The reaction between NO3 and several certain hydrocarbons (e.g. isoprene) is known to produce organic nitrates and form SOA (Ng et al., 2008; Ng et al., 2017). Fig. 7 shows the organic nitrate production rate from hydrocarbons reacting with NO3 and OH. The production of organic nitrate in RACM2 includes ISON (defined as β-hydroxyalkylnitrates and alkylnitrates) and ONIT (other organic nitrates except ISON) (Geiger et al., 2003). The mean diurnal profile showed that the OH reaction was responsible for daytime organic nitrate formation and that the NO3 reaction was responsible for the nighttime formation. The NO3 nighttime chemistry had a higher organic nitrate yield with an average value of 0.06 ppbv/h in the nighttime than that of OH in the daytime, but the two paths had the same contribution to the total nitrate production because the duration of daytime was longer than that of nighttime.

NO2 + OH → HNO3

Fig. 7. The estimation of the organic nitrate (OrgN) production rate, the connected red and blue dot represents the contribution from the reacting OH with VOCs and the reacting of NO3 with VOCs, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

The OH and NO2 data were used in the field observation results in this campaign, and the rate constant of this reaction is 1.08 × 1011 cm3 molecules− 1 s− 1 at 295 K (Sander et al., 2011). The nighttime NOx removal evaluation can be substituted by calculating the production rate of NO3 when the NO3 lifetime is short enough and the NO effect is negligible (Stutz et al., 2010), which can be more constrained by subtracting the morning residuals of ClNO2 and N2O5 (Tsai et al., 2014), releasing NO2 back to the ambient environment by photolysis reaction after sunrise in the next morning. However, in this study, the method mentioned above is not suitable because the NO contribution to NO3 loss is dominant. The effective NOx removal paths should include the reaction of NO3 with VOC, N2O5 hydrolysis, NO3 heterogeneous uptake and the N2O5 homogeneous reaction. Here, we simply regarded the latter two items as negligible (Brown and Stutz, 2012) and assumed that NO3 reacting with VOC removed one NOx molecule. The removal efficiency was one unit per initial reaction, and the efficiency of NOx removal and NO3− production from N2O5 hydrolysis was 2-ϕ(ClNO2) from R6. The daily peaks of the loss rate of NOx (LNOX) in the daytime ranged from 2 ppbv/h to 8 ppbv/h, while the daily peaks of nighttime LNOX ranged from 0.1 ppbv/h to 0.7 ppbv/h. Fig. 9 shows the averaged contribution of the NOx removal over a 24-h period. Because the

3.5. NOx removal NO3 and N2O5 chemistry promoted the emission of NOx by anthropic activity and converted it to organic nitrate or NO3−, which were then removed by a subsequent reaction and deposition. To evaluate the importance of the nighttime NOx loss in the Yufa site, we compared the nighttime NOX loss with the daytime NOx removal over a 24 period and ignored the vertical effect in the nighttime boundary layer (NBL) to obtain insight into the nighttime contribution of NOx removal in the surface layer atmosphere. Primary NOx removal in the daytime mainly contributes to the conversion of NO2 to HNO3 through the reaction of NO2 with OH (R12).

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Fig. 8. (a) the particle nitrate NO3− enhancement event happened on the night of 23–24 August, the blue line represents the observation result, the red line represents the calculated integral NO3− from N2O5 heterogeneous uptake with an offset of 10 μg/m3; (b) the same on the night of 24–25 August with the offset of 6 μg/m3. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

3.6. Nocturnal chloride activation and its impact We evaluated the impact of the chloride activation caused by N2O5 uptake and analyzed the average condition as well as the special case of high ClNO2 occurring on 24 August. Fig. 10(a) depicts the production rate of Cl with and without ClNO2 chemistry, and the peak of the average Cl production rate was up to 0.22 ppbv/h when ClNO2 chemistry was included, which was much larger than that when ClNO2 chemistry was excluded (the average of the production rate was less than 0.02 ppbv/h). ClNO2 photolysis predominantly yielded Cl and peaked at approximately 10:00 in the morning. Other sources, such as Cl2 photolysis and the reaction of HCl with OH, by contrast, were very small, as in previous studies (Riedel et al., 2014; Tham et al., 2014; Tham et al., 2016). Fig. 10(b) shows that the high ClNO2 case occurred on the night of 24 August and that the Cl production rate reached 0.75 ppbv/h because of the elevated ClNO2 photolysis, which was approximately three-fold higher than the under average conditions. Fig. 10(c) shows that the primary ROx production rate included the ClNO2 chemistry in an average situation and that the primary ROx was derived from O3 + VOCs, Cl + VOCs, NO3 oxidation and the photolysis of ClNO2, OVOCs (excluding HCHO), HCHO, HONO and O3 (O1D + H2O). The morning ROx production sources were dominated by HONO and HCHO photolysis, as shown by our previous results in Beijing (Lu et al., 2013), and the mean contribution from Cl oxidation was approximately 5.0% (08:00–08:30), which was much lower than the result from North China Plain reported by Tham et al. (2016). If added the contribution from HONO, the accumulated reactive nitrogen compounds during nighttime towards the primary radical formation is larger than 50% before 9:00, which is comparable with those in Los Angles (Young et al., 2012, 2014). In the high ClNO2 case, the contribution to ROx production was approximately 13% over the same time period (shown in Fig. 10(d)). Compared with the average case, the high ClNO2 case had the same or even a lower total ROX production rate, demonstrating that high ClNO2 cannot elevate the total production of ROx but change the distributions from different pathways. Additionally, Fig. 10(c) shows that NO3 oxidation was particularly important for ROx production in the nighttime, which accounted for over 50% of the primary ROx, like that reported in previous modeling studies (Geyer et al., 2003). The effect of ClNO2 chemistry on daytime O3 formation was determined at this site. In the average case, ClNO2 photolysis enhanced O3 production and increased the net O3 production to 1.0 ppbv/h, and the enhancement was approximately 8% during the morning (08:00–10:00); in the high ClNO2 case, the O3 production enhancement was even more remarkable. The peak of the extra net O3 production rate reached up to 3.0 ppbv/h at 11:00, and the enhancement was approximately 31% during the morning (08:00–10:00). Fig. 11(a) plots the extra integral net O3 formation caused by ClNO2 photolysis in the average case and high ClNO2 case. In the average case, the ClNO2 chemistry increased O3 to

Fig. 9. The box represents the integral NOx removal contribution in 24-h period (ppbv), the daytime NOx removal caused by the reacting OH with NO2, the nighttime NOx removed by the NO3 reacted with VOC (green) and the N2O5 hydrolysis (red) minus the NOx removal potential from ClNO2 (white). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

duration of daytime was longer than that of nighttime (14 and 10 h, respectively), the daytime integral NOx removal was 23.9 ppbv and the nighttime integral NOx removal due to the reaction of NO3 with VOC and N2O5 hydrolysis was 2.0 ppbv and 1.6 ppbv, respectively. The results showed that the nocturnal chemistry led to a relatively small but non-ignorable contribution to the total NOx removal (13%) over the 24h period, even when ϕ(ClNO2) dropped to zero. The potential of additional NOx removal only added approximately 1.0 ppbv and contributed approximately 16%, but it only represented the situation in the surface layer and was not like the result of previous studies, which considered the effect of the vertical variation of NBL and found that the nocturnal chemistry had a significant contribution to NOx removal, which was even higher than the daytime removal due to the reaction of OH with NO2 (Stutz et al., 2010; Wagner et al., 2013; Tsai et al., 2014). A high mixing ratio of NO in the surface layer atmosphere suppressed NO3 and limited NOx removal. Several studies confirmed that NO had a clear vertical variation and was consumed effectively above the surface layer atmosphere, allowing us to predict that the nighttime chemistry may make a more significant contribution to NOx removal above the surface layer in Beijing. 104

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Fig. 10. (a, b) The diurnal variation of the production rate of Cl radical with and without ClNO2 chemistry, (c, d) the distribution of diurnal variation of the primary production rate of ROx. (a, c) represents the average case and (b, d) represents the high ClNO2 case happed on the night of 24 August.

4. Conclusions

approximately 5.0 ppbv before 11:00 am and was approximately 5.8 ppbv throughout the day, on average. These values were similar with previous studies in Houston, NCP and Hong Kong (Osthoff et al., 2008; Xue et al., 2015; T. Wang et al., 2016; Tham et al., 2016). In the high ClNO2 condition, the net O3 enhancement was much higher, with a value of approximately 11.0 ppbv before 11:00, which was twice as high as that of the average case. HONO was the main source of O3 formation, and Fig. 11(b) shows the net O3 production with and without HONO input in the average case and high ClNO2 case. In the average case, the integral net O3 production caused by HONO reached 25 ppbv until 11:00, which was much higher than that from ClNO2. In contrast to the high ClNO2 case on 24 August, the contribution of HONO to O3 production was similar to the average case before 11:00. In this condition, the contribution of ClNO2 seemed to be comparable with that of HONO, meaning that ClNO2 may have an important effect on the air quality in NCP and other high chloride aerosol regions.

NO3, N2O5 and ClNO2 were studied by a box model simulation at a rural site in Beijing. The high production rate of NO3 and low mixing ratio indicated that nighttime chemistry was non-negligible relative to daytime NOx chemistry. The modeling studies suggested a significant contribution of N2O5 heterogeneous uptake towards the nighttime NO3− particle enhancement. The NOX removal by nighttime chemistry was limited and much lower than reported in previous studies, but a high contribution to NOx removal by NO3 and N2O5 chemistry above the surface layer may have existed in NCP, and need to be explored by a vertical field campaign. Chloride activation by N2O5 heterogeneous uptake on the chloride aerosols increased primary ROx formation by 5% and accounted for 8% of the net O3 production enhancement before noon. These results demonstrated that the nighttime chemistry was closely related to the air quality, and more field campaigns and model work need to be conducted.

Fig. 11. (a) The integral net O3 producing enhancement caused by ClNO2 in the 24-h period at average condition (black dot) and at high ClNO2 condition (red dot) on 24th August, respectively; (b) The integral net O3 producing enhancement caused by HONO in the 24 h period at average condition (black dot) and at high ClNO2 condition (red dot), respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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Gaston, C.J., Thornton, J.A., Ng, N.L., 2014. Reactive uptake of N2O5 to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separations. Atmos. Chem. Phys. 14, 5693–5707. http://dx.doi. org/10.5194/acp-14-5693-2014. Geiger, H., Barnes, I., Bejan, I., Benter, T., Spittler, M., 2003. The tropospheric degradation of isoprene: an updated module for the regional atmospheric chemistry mechanism. Atmos. Environ. 37, 1503–1519. http://dx.doi.org/10.1016/S13522310(02)01047-6. Geyer, A., et al., 2001. Chemistry and oxidation capacity of the nitrate radical in the continental boundary layer near Berlin. J. Geophys. Res.-Atmos. 106, 8013–8025. http://dx.doi.org/10.1029/2000jd900681. Geyer, A., et al., 2003. Nighttime formation of peroxy and hydroxyl radicals during the BERLIOZ campaign: observations and modeling studies. J. Geophys. Res.-Atmos. 108, Artn 8249. http://dx.doi.org/10.1029/2001jd000656. Geyer, A., Stutz, J., 2004. Vertical profiles of NO3, N2O5, O3, and NOx in the nocturnal boundary layer: 2. Model studies on the altitude dependence of composition and chemistry (vol 109, art no D16399, 2004). J. Geophys. Res.-Atmos. 109, Artn D16399. http://dx.doi.org/10.1029/2004jd005217. Ghosh, B., Papanastasiou, D.K., Talukdar, R.K., Roberts, J.M., Burkholder, J.B., 2012. Nitryl chloride (CINO2): UV/Vis absorption Spectrum between 210 and 296 K and O (P-3) quantum yield at 193 and 248 nm. J. Phys. Chem. A 116, 5796–5805. http://dx. doi.org/10.1021/jp207389y. Goliff, W.S., Stockwell, W.R., Lawson, C.V., 2013. The regional atmospheric chemistry mechanism, version 2. Atmos. Environ. 68, 174–185. http://dx.doi.org/10.1016/j. atmosenv.2012.11.038. Griffiths, P.T., et al., 2009. Reactive uptake of N2O5 by aerosols containing dicarboxylic acids. Effect of particle phase, composition, and nitrate content. J. Phys. Chem. A 113, 5082–5090. http://dx.doi.org/10.1021/Jp8096814. Grzinic, G., Bartels-Rausch, T., Berkemeier, T., Turler, A., Ammann, M., 2015. Viscosity controls humidity dependence of N2O5 uptake to citric acid aerosol. Atmos. Chem. Phys. 15, 13615–13625. http://dx.doi.org/10.5194/acp-15-13615-2015. Hallquist, M., Stewart, D.J., Stephenson, S.K., Cox, R.A., 2003. Hydrolysis of N2O5 on submicron sulfate aerosols. Phys. Chem. Chem. Phys. 5, 3453–3463. http://dx.doi.org/ 10.1039/B301827j. Huang, R.J., et al., 2014. High secondary aerosol contribution to particulate pollution during haze events in China. Nature 514, 218–222. http://dx.doi.org/10.1038/ nature13774. Kane, S.M., Caloz, F., Leu, M.T., 2001. Heterogeneous uptake of gaseous N2O5 by (NH4)2SO4, NH4HSO4, and H2SO4 aerosols. J. Phys. Chem. A 105, 6465–6470. http:// dx.doi.org/10.1021/Jp010490x. Khan, M.A.H., et al., 2015. Global modeling of the nitrate radical (NO3) for present and pre-industrial scenarios. Atmos. Res. 164, 347–357. http://dx.doi.org/10.1016/j. atmosres.2015.06.006. Kiendler-Scharr, A., et al., 2016. Ubiquity of organic nitrates from nighttime chemistry in the European submicron aerosol. Geophys. Res. Lett. 43, 7735–7744. http://dx.doi. org/10.1002/2016gl069239. Knopf, D.A., Cosman, L.M., Mousavi, P., Mokamati, S., Bertram, A.K., 2007. A novel flow reactor for studying reactions on liquid surfaces coated by organic monolayers: methods, validation, and initial results. J. Phys. Chem. A 111, 11021–11032. http:// dx.doi.org/10.1021/Jp075724c. Knopf, D.A., Forrester, S.M., Slade, J.H., 2011. Heterogeneous oxidation kinetics of organic biomass burning aerosol surrogates by O3, NO2, N2O5, and NO3. Phys. Chem. Chem. Phys. 13, 21050–21062. http://dx.doi.org/10.1039/c1cp22478f. Li, Q.Y., et al., 2016. Impacts of heterogeneous uptake of dinitrogen pentoxide and chlorine activation on ozone and reactive nitrogen partitioning: improvement and application of the WRF-Chem model in southern China. Atmos. Chem. Phys. 16, 14875–14890. http://dx.doi.org/10.5194/acp-16-14875-2016. Li, X., et al., 2012. Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in southern China. Atmos. Chem. Phys. 12, 1497–1513. http://dx.doi.org/10. 5194/acp-12-1497-2012. Liu, X.G., et al., 2013. Increase of aerosol scattering by hygroscopic growth: observation, modeling, and implications on visibility. Atmos. Res. 132, 91–101. http://dx.doi.org/ 10.1016/j.atmosres.2013.04.007. Liu, Z.R., Hu, B., Zhang, J.K., Yu, Y.C., Wang, Y.S., 2016. Characteristics of aerosol size distributions and chemical compositions during wintertime pollution episodes in Beijing. Atmos. Res. 168, 1–12. http://dx.doi.org/10.1016/j.atmosres.2015.08.013. Lu, K.D., et al., 2013. Missing OH source in a suburban environment near Beijing: observed and modelled OH and HO2 concentrations in summer 2006. Atmos. Chem. Phys. 13, 1057–1080. http://dx.doi.org/10.5194/acp-13-1057-2013. Lu, K.D., et al., 2014. Nighttime observation and chemistry of HOx in the Pearl River Delta and Beijing in summer 2006. Atmos. Chem. Phys. 14, 4979–4999. http://dx. doi.org/10.5194/acp-14-4979-2014. McLaren, R., et al., 2004. Nighttime chemistry at a rural site in the Lower Fraser Valley. Atmos. Environ. 38, 5837–5848. http://dx.doi.org/10.1016/j.atmosenv.2004.03. 074. McNeill, V.F., Patterson, J., Wolfe, G.M., Thornton, J.A., 2006. The effect of varying levels of surfactant on the reactive uptake of N2O5 to aqueous aerosol. Atmos. Chem. Phys. 6, 1635–1644. Mentel, T.F., Sohn, M., Wahner, A., 1999. Nitrate effect in the heterogeneous hydrolysis of dinitrogen pentoxide on aqueous aerosols. Phys. Chem. Chem. Phys. 1, 5451–5457. http://dx.doi.org/10.1039/A905338g. Mielke, L.H., Furgeson, A., Odame-Ankrah, C.A., Osthoff, H.D., 2016. Ubiquity of ClNO2 in the urban boundary layer of Calgary, Alberta, Canada. Can. J. Chem. 94, 414–423. http://dx.doi.org/10.1139/cjc-2015-0426. Mielke, L.H., et al., 2013. Heterogeneous formation of nitryl chloride and its role as a nocturnal NOx reservoir species during CalNex-LA 2010. J. Geophys. Res.-Atmos.

Acknowledgements The work was supported by the National Natural Science Foundation of China (Grants No. 41375124,21522701, 91544225, 41421064) and Strategic Priority Research Program of the Chinese Academy of Sciences (grant no. XDB05010500). The authors gratefully acknowledge the CAREBeijing-2006 science team, especially S. Guo, X. H. Wang, N. Takegawa for technical help and support at the field site, A. Nowak for providing aerosol surface-area density data, and X. Liu for providing measured LIDAR data of the atmospheric boundary layer height. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.atmosres.2017.06.013. References Aldener, M., et al., 2006. Reactivity and loss mechanisms of NO3 and N2O5 in a polluted marine environment: Results from in situ measurements during New England Air Quality Study 2002. J. Geophys. Res.-Atmos. 111, Artn D23s73. http://dx.doi.org/ 10.1029/2006jd007252. Anttila, T., Kiendler-Scharr, A., Tillmann, R., Mentel, T.F., 2006. On the reactive uptake of gaseous compounds by organic-coated aqueous aerosols: theoretical analysis and application to the heterogeneous hydrolysis of N2O5. J. Phys. Chem. A 110, 10435–10443. http://dx.doi.org/10.1021/Jp062403c. Atkinson, R., Arey, J., 2003. Gas-phase tropospheric chemistry of biogenic volatile organic compounds: a review. Atmos. Environ. 37, S197–S219. http://dx.doi.org/10. 1016/S1352-2310(03)00391-1. Atkinson, R., et al., 2004. Evaluated kinetic and photochemical data for atmospheric chemistry: volume I - gas phase reactions of Ox, HOx, NOx and SOx species. Atmos. Chem. Phys. 4, 1461–1738 (SRef-ID: 1680-7324/acp/2004-4-1461). Atkinson, R., et al., 2006. Evaluated kinetic and photochemical data for atmospheric chemistry: volume II - gas phase reactions of organic species. Atmos. Chem. Phys. 6, 3625–4055. Bertram, T.H., Thornton, J.A., 2009. Toward a general parameterization of N2O5 reactivity on aqueous particles: the competing effects of particle liquid water, nitrate and chloride. Atmos. Chem. Phys. 9, 8351–8363. Brown, S.S., et al., 2009. Reactive uptake coefficients for N2O5 determined from aircraft measurements during the second Texas air quality study: comparison to current model parameterizations. J. Geophys. Res.-Atmos. 114, Artn D00f10. http://dx.doi. org/10.1029/2008jd011679. Brown, S.S., et al., 2007a. Vertical profiles in NO3 and N2O5 measured from an aircraft: Results from the NOAA P-3 and surface platforms during the New England air quality study 2004. J. Geophys. Res.-Atmos. 112, Artn D22304. http://dx.doi.org/10.1029/ 2007jd008883. Brown, S.S., et al., 2007b. High resolution vertical distributions of NO3 and N2O5 through the nocturnal boundary layer. Atmos. Chem. Phys. 7, 139–149. Brown, S.S., et al., 2016. Nighttime chemistry at a high altitude site above Hong Kong. J. Geophys. Res.-Atmos. 121, 2457–2475. http://dx.doi.org/10.1002/2015jd024566. Brown, S.S., et al., 2006. Variability in nocturnal nitrogen oxide processing and its role in regional air quality. Science 311, 67–70. http://dx.doi.org/10.1126/science. 1120120. Brown, S.S., Stark, H., Ravishankara, A.R., 2003. Applicability of the steady state approximation to the interpretation of atmospheric observations of NO3 and N2O5. J. Geophys. Res.-Atmos. 108, Artn 4539. http://dx.doi.org/10.1029/2003jd003407. Brown, S.S., Stutz, J., 2012. Nighttime radical observations and chemistry. Chem. Soc. Rev. 41, 6405–6447. http://dx.doi.org/10.1039/C2cs35181a. Cosman, L.M., Bertram, A.K., 2008a. Reactive uptake of N2O5 on aqueous H2SO4 solutions coated with 1-component and 2-component monolayers. J. Phys. Chem. A 112, 4625–4635. http://dx.doi.org/10.1021/Jp8005469. Cosman, L.M., Knopf, D.A., Bertram, A.K., 2008b. N2O5 reactive uptake on aqueous sulfuric acid solutions coated with branched and straight-chain insoluble organic surfactants. J. Phys. Chem. A 112, 2386–2396. http://dx.doi.org/10.1021/Jp710685r. Crounse, J.D., Paulot, F., Kjaergaard, H.G., Wennberg, P.O., 2011. Peroxy radical isomerization in the oxidation of isoprene. Phys. Chem. Chem. Phys. 13, 13607–13613. http://dx.doi.org/10.1039/c1cp21330j. Crowley, J.N., et al., 2010. Nocturnal nitrogen oxides at a rural mountain-site in southwestern Germany. Atmos. Chem. Phys. 10, 2795–2812. Dentener, F.J., Crutzen, P.J., 1993. Reaction of N2O5 on tropospheric aerosols - impact on the global distributions of NOx, O3, and OH. J. Geophys. Res.-Atmos. 98, 7149–7163. http://dx.doi.org/10.1029/92jd02979. Dong, H.B., et al., 2012. Technical note: the application of an improved gas and aerosol collector for ambient air pollutants in China. Atmos. Chem. Phys. 12, 10519–10533. http://dx.doi.org/10.5194/acp-12-10519-2012. Garland, R.M., et al., 2009. Aerosol optical properties observed during Campaign of Air Quality Research in Beijing 2006 (CAREBeijing-2006): characteristic differences between the inflow and outflow of Beijing city air. J. Geophys. Res.-Atmos. 114, Artn D00g04. http://dx.doi.org/10.1029/2008jd010780.

106

Atmospheric Research 196 (2017) 97–107

H. Wang et al.

region of northern China. Atmos. Chem. Phys. 16, 14959–14977. http://dx.doi.org/ 10.5194/acp-16-14959-2016. Tham, Y.J., et al., 2014. Presence of high nitryl chloride in Asian coastal environment and its impact on atmospheric photochemistry. Chin. Sci. Bull. 59, 356–359. http://dx. doi.org/10.1007/s11434-013-0063-y. Thornton, J.A., Abbatt, J.P.D., 2005. N2O5 reaction on submicron sea salt aerosol: kinetics, products, and the effect of surface active organics. J. Phys. Chem. A 109, 10004–10012. http://dx.doi.org/10.1021/Jp054183t. Thornton, J.A., Braban, C.F., Abbatt, J.P.D., 2003. N2O5 hydrolysis on sub-micron organic aerosols: the effect of relative humidity, particle phase, and particle size. Phys. Chem. Chem. Phys. 5, 4593–4603. http://dx.doi.org/10.1039/B307498f. Thornton, J.A., et al., 2010. A large atomic chlorine source inferred from mid-continental reactive nitrogen chemistry. Nature 464, 271–274. http://dx.doi.org/10.1038/ Nature08905. Tsai, C., et al., 2014. Nocturnal loss of NOx during the 2010 CalNex-LA study in the Los Angeles Basin. J. Geophys. Res.-Atmos. 119, 13004–13025. http://dx.doi.org/10. 1002/2014jd022171. Wagner, N.L., et al., 2013. N2O5 uptake coefficients and nocturnal NO2 removal rates determined from ambient wintertime measurements. J. Geophys. Res.-Atmos. 118, 9331–9350. http://dx.doi.org/10.1002/Jgrd.50653. Wahner, A., Mentel, T.F., Sohn, M., 1998. Gas-phase reaction of N2O5 with water vapor: importance of heterogeneous hydrolysis of N2O5 and surface desorption of HNO3 in a large teflon chamber. Geophys. Res. Lett. 25, 2169–2172. http://dx.doi.org/10. 1029/98gl51596. Wang, H.C., Lu, K.D., 2016. Determination and parameterization of the heterogeneous uptake coefficient of dinitrogen pentoxide (N2O5). Prog. Chem. 28, 917–933. http:// dx.doi.org/10.7536/Pc151225. Wang, S.S., et al., 2013. Observation of NO3 radicals over Shanghai, China. Atmos. Environ. 70, 401–409. http://dx.doi.org/10.1016/j.atmosenv.2013.01.022. Wang, T., et al., 2016. Observations of nitryl chloride and modeling its source and effect on ozone in the planetary boundary layer of southern China. J. Geophys. Res.-Atmos. 121, 2476–2489. http://dx.doi.org/10.1002/2015jd024556. Wangberg, I., Etzkorn, T., Barnes, I., Platt, U., Becker, K.H., 1997. Absolute determination of the temperature behavior of the NO2 +NO3 +(M) < − > N2O5 +(M) equilibrium. J. Phys. Chem. A 101, 9694–9698. http://dx.doi.org/10.1021/jp972203o. Wayne, R.P., et al., 1991. The nitrate radical - Physics, Chemistry, and the atmosphere. Atmos. Environ. 25, 1–203. http://dx.doi.org/10.1016/0960-1686(91)90192-A. Weller, C., Herrmann, H., 2015. Kinetics of nitrosamine and amine reactions with NO3 radical and ozone related to aqueous particle and cloud droplet chemistry. Atmos. Res. 151, 64–71. http://dx.doi.org/10.1016/j.atmosres.2014.02.023. Wu, Q.Z., et al., 2011. A numerical study of contributions to air pollution in Beijing during CAREBeijing-2006. Atmos. Chem. Phys. 11, 5997–6011. http://dx.doi.org/10. 5194/acp-11-5997-2011. Wu, Z.J., et al., 2017. Chemical and physical properties of biomass burning aerosols and their CCN activity: a case study in Beijing, China. Sci. Total Environ. 579, 1260–1268. http://dx.doi.org/10.1016/j.scitotenv.2016.11.112. Xue, L.K., et al., 2015. Development of a chlorine chemistry module for the master chemical mechanism. Geosci. Model Dev. 8, 3151–3162. http://dx.doi.org/10.5194/ gmd-8-3151-2015. Ye, N.N., et al., 2016. A study of the water-soluble inorganic salts and their gaseous precursors at wangdu site in the summer time. Acta Sci. Nat. Univ. Pekin. 52, 1109–1117. http://dx.doi.org/10.13209/j.0479-8023.2016.116. (Chinese). Young, C.J., et al., 2014. Chlorine as a primary radical: evaluation of methods to understand its role in initiation of oxidative cycles. Atmos. Chem. Phys. 14, 3427–3440. http://dx.doi.org/10.5194/acp-14-3427-2014. Young, C.J., et al., 2012. Vertically resolved measurements of nighttime radical reservoirs; in Los Angeles and their contribution to the urban radical budget. Environ Sci Technol 46, 10965–10973. http://dx.doi.org/10.1021/es302206a. Yuan, Z.B., et al., 2009. Source analysis of volatile organic compounds by positive matrix factorization in urban and rural environments in Beijing. J. Geophys. Res.-Atmos. 114. http://dx.doi.org/10.1029/2008jd011190. Yue, D.L., et al., 2009. Characteristics of aerosol size distributions and new particle formation in the summer in Beijing. J. Geophys. Res.-Atmos. 114. http://dx.doi.org/10. 1029/2008jd010894.

118, 10638–10652. http://dx.doi.org/10.1002/Jgrd.50783. Morgan, W.T., et al., 2015. Influence of aerosol chemical composition on N2O5 uptake: airborne regional measurements in northwestern Europe. Atmos. Chem. Phys. 15, 973–990. http://dx.doi.org/10.5194/acp-15-973-2015. Ng, N.L., et al., 2017. Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms, and organic aerosol. Atmos. Chem. Phys. 17, 2103–2162. http:// dx.doi.org/10.5194/acp-17-2103-2017. Ng, N.L., et al., 2008. Secondary organic aerosol (SOA) formation from reaction of isoprene with nitrate radicals (NO3). Atmos. Chem. Phys. 8, 4117–4140. Osthoff, H.D., et al., 2008. High levels of nitryl chloride in the polluted subtropical marine boundary layer. Nat. Geosci. 1, 324–328. http://dx.doi.org/10.1038/Ngeo177. Pathak, R.K., Wang, T., Wu, W.S., 2011. Nighttime enhancement of PM2.5 nitrate in ammonia-poor atmospheric conditions in Beijing and Shanghai: plausible contributions of heterogeneous hydrolysis of N2O5 and HNO3 partitioning. Atmos. Environ. 45, 1183–1191. http://dx.doi.org/10.1016/j.atmosenv.2010.09.003. Pathak, R.K., Wu, W.S., Wang, T., 2009. Summertime PM2.5 ionic species in four major cities of China: nitrate formation in an ammonia-deficient atmosphere. Atmos. Chem. Phys. 9, 1711–1722. Peeters, J., Muller, J.F., Stavrakou, T., Nguyen, V.S., 2014. Hydroxyl radical recycling in isoprene oxidation driven by hydrogen bonding and hydrogen tunneling: the upgraded LIM1 mechanism. J. Phys. Chem. A 118, 8625–8643. http://dx.doi.org/10. 1021/jp5033146. Phillips, G.J., et al., 2012. Significant concentrations of nitryl chloride observed in rural continental Europe associated with the influence of sea salt chloride and anthropogenic emissions. Geophys. Res. Lett. 39, Artn L10811. http://dx.doi.org/10.1029/ 2012gl051912. Phillips, G.J., et al., 2016. Estimating N2O5 uptake coefficients using ambient measurements of NO3, N2O5, ClNO2 and particle-phase nitrate. Atmos. Chem. Phys. 16, 13231–13249. http://dx.doi.org/10.5194/acp-16-13231-2016. Richter, A., Burrows, J.P., Nuss, H., Granier, C., Niemeier, U., 2005. Increase in tropospheric nitrogen dioxide over China observed from space. Nature 437, 129–132. http://dx.doi.org/10.1038/nature04092. Riedel, T.P., et al., 2012. Direct N2O5 reactivity measurements at a polluted coastal site. Atmos. Chem. Phys. 12, 2959–2968. http://dx.doi.org/10.5194/acp-12-2959-2012. Riedel, T.P., et al., 2014. An MCM modeling study of nitryl chloride (ClNO2) impacts on oxidation, ozone production and nitrogen oxide partitioning in polluted continental outflow. Atmos. Chem. Phys. 14, 3789–3800. http://dx.doi.org/10.5194/acp-143789-2014. Sander, S.P., et al., 2011. Chemical kinetics and photochemical data for use in atmospheric studies, evaluation number 17. Pasadena, Calif. Sarwar, G., Simon, H., Bhave, P., Yarwood, G., 2012. Examining the impact of heterogeneous nitryl chloride production on air quality across the United States. Atmos. Chem. Phys. 12, 6455–6473. http://dx.doi.org/10.5194/acp-12-6455-2012. Sarwar, G., Simon, H., Xing, J., Mathur, R., 2014. Importance of tropospheric ClNO2 chemistry across the northern hemisphere. Geophys. Res. Lett. 41, 4050–4058. http://dx.doi.org/10.1002/2014gl059962. Shon, Z.H., et al., 2013. Analysis of water-soluble ions and their precursor gases over diurnal cycle. Atmos. Res. 132, 309–321. http://dx.doi.org/10.1016/j.atmosres. 2013.06.003. Simon, H., et al., 2009. Modeling the impact of ClNO2 on ozone formation in the Houston area. J. Geophys. Res.-Atmos. 114, Artn D00f03. http://dx.doi.org/10.1029/ 2008jd010732. Sobanski, N., et al., 2016. Chemical and meteorological influences on the lifetime of NO3 at a semi-rural mountain site during PARADE. Atmos. Chem. Phys. 16, 4867–4883. http://dx.doi.org/10.5194/acp-16-4867-2016. Stutz, J., et al., 2010. Nocturnal NO3 radical chemistry in Houston, TX. Atmos. Environ. 44, 4099–4106. http://dx.doi.org/10.1016/j.atmosenv.2009.03.004. Takegawa, N., et al., 2009. Variability of submicron aerosol observed at a rural site in Beijing in the summer of 2006. J. Geophys. Res.-Atmos. 114, Artn D00g05. http://dx. doi.org/10.1029/2008jd010857. Tan, Z., et al., 2017. Radical chemistry at a rural site (Wangdu) in the North China Plain: observation and model calculations of OH, HO2 and RO2 radicals. Atmos. Chem. Phys. 17, 663–690. http://dx.doi.org/10.5194/acp-17-663-2017. Tham, Y.J., et al., 2016. Significant concentrations of nitryl chloride sustained in the morning: investigations of the causes and impacts on ozone production in a polluted

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