scholarly journals Production of N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> in summer in urban Beijing, China

2018 ◽  
Vol 18 (16) ◽  
pp. 11581-11597 ◽  
Author(s):  
Wei Zhou ◽  
Jian Zhao ◽  
Bin Ouyang ◽  
Archit Mehra ◽  
Weiqi Xu ◽  
...  
Keyword(s):  
Urban Areas ◽  
Product Formation ◽  
High Reactivity ◽  
Ionization Mass ◽  
Dinitrogen Pentoxide ◽  
Mixing Ratios ◽  
Nitryl Chloride ◽  
Volatile Organic ◽  
Beijing China ◽  
Hydrolysis Of

Abstract. The heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) has a significant impact on both nocturnal particulate nitrate formation and photochemistry on the following day through the photolysis of nitryl chloride (ClNO2), yet these processes in highly polluted urban areas remain poorly understood. Here we present measurements of gas-phase N2O5 and ClNO2 by high-resolution time-of-flight chemical ionization mass spectrometer (ToF-CIMS) during summer in urban Beijing, China as part of the Air Pollution and Human Health (APHH) campaign. N2O5 and ClNO2 show large day-to-day variations with average (±1σ) mixing ratios of 79.2±157.1 and 174.3±262.0 pptv, respectively. High reactivity of N2O5, with τ (N2O5)−1 ranging from 0.20 × 10−2 to 1.46 × 10−2 s−1, suggests active nocturnal chemistry and a large nocturnal nitrate formation potential via N2O5 heterogeneous uptake. The lifetime of N2O5, τ (N2O5), decreases rapidly with the increase in aerosol surface area, yet it varies differently as a function of relative humidity with the highest value peaking at ∼ 40 %. The N2O5 uptake coefficients estimated from the product formation rates of ClNO2 and particulate nitrate are in the range of 0.017–0.19, corresponding to direct N2O5 loss rates of 0.00044–0.0034 s−1. Further analysis indicates that the fast N2O5 loss in the nocturnal boundary layer in urban Beijing is mainly attributed to its indirect loss via NO3, for example through the reactions with volatile organic compounds and NO, while the contribution of the heterogeneous uptake of N2O5 is comparably small (7–33 %). High ClNO2 yields ranging from 0.10 to 0.35 were also observed, which might have important implications for air quality by affecting nitrate and ozone formation.

scholarly journals Production of N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> in summer in urban Beijing, China

2018 ◽  
Author(s):  
Wei Zhou ◽  
Jian Zhao ◽  
Bin Ouyang ◽  
Archit Mehra ◽  
Weiqi Xu ◽  
...  
Keyword(s):  
Urban Areas ◽  
Life Time ◽  
Product Formation ◽  
High Reactivity ◽  
Ionization Mass ◽  
Mass Spectrometers ◽  
Dinitrogen Pentoxide ◽  
Mixing Ratios ◽  
Beijing China ◽  
Hydrolysis Of

Abstract. The heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) has a significant impact on both nocturnal particulate nitrate formation and photochemistry the following day through photolysis of nitryl chloride (ClNO2), yet these processes in highly polluted urban areas remain poorly understood. Here we present measurements of gas-phase N2O5 and ClNO2 by high-resolution time-of-flight chemical ionization mass spectrometers (ToF-CIMS) during summer in urban Beijing, China as part of the Air Pollution and Human Health (APHH) campaign. N2O5 and ClNO2 show large day-to-day variations with average (±1σ) mixing ratios of 79.2 ± 157.1 and 174.3 ± 262.0 pptv, respectively. High reactivity of N2O5, with τ (N2O5)−1 ranging from 0.20 × 10−2 to 1.46 × 10−2 s−1, suggests active nocturnal chemistry and a large nocturnal nitrate formation potential via N2O5 heterogeneous uptake. The life time of N2O5, τ(N2O5), decreases rapidly as the increase of aerosol surface area, yet it varies differently as a function of relative humidity with the highest value peaking at ~ 40 %. The N2O5 uptake coefficients estimated from the product formation rates of ClNO2 and particulate nitrate are in the range of 0.017–0.19, corresponding to direct N2O5 loss rates of 0.00044–0.0034 s−1. Further analysis indicates that the fast N2O5 loss in the nocturnal boundary layer in urban Beijing is mainly attributed to its indirect loss via NO3, for example through the reactions with volatile organic compounds and NO, while the contribution of heterogeneous uptake of N2O5 is comparably small (7–33 %). High ClNO2 yields ranging from 0.10 to 0.35 were also observed which might have important implications for air quality by affecting nitrate and ozone formation.

scholarly journals Significant concentrations of nitryl chloride sustained in the morning: Investigations of the causes and impacts on ozone production in a polluted region of northern China

2016 ◽  
Author(s):  
Yee Jun Tham ◽  
Zhe Wang ◽  
Qinyi Li ◽  
Hui Yun ◽  
Weihao Wang ◽  
...  
Keyword(s):  
Inversion Layer ◽  
Northern China ◽  
Residual Layer ◽  
Ozone Production ◽  
Rural Site ◽  
Ionization Mass ◽  
Dinitrogen Pentoxide ◽  
Mixing Ratios ◽  
Nitryl Chloride ◽  
Nocturnal Inversion

Abstract. Nitryl chloride (ClNO2) is a dominant source of chlorine radical in polluted environment and can significantly affect the atmospheric oxidative chemistry. However, the abundance of ClNO2 and its exact role are not fully understood under different environmental conditions. During the summer of 2014, we deployed a chemical ionization mass spectrometer to measure ClNO2 and dinitrogen pentoxide (N2O5) at a rural site in the polluted North China Plain. Elevated mixing ratios of ClNO2 (> 350 pptv) were observed at most of the nights with low levels of N2O5 (< 200 pptv). The highest ClNO2 mixing ratio of 2070 pptv (1-min average) was observed in a plume from megacity (Tianjin) and was characterized with faster N2O5 heterogeneous loss rate and ClNO2 production rate compared to average condition. The abundant ClNO2 concentration kept increasing even after sunrise and reached a peak 4 hours later. Such highly sustained ClNO2 peaks after sunrise are discrepant from the previously observed typical diurnal pattern. Meteorological and chemical analysis show that the sustained ClNO2 morning peaks are caused by significant ClNO2 production in the residual layer at night followed by downward mixing after break-up of the nocturnal inversion layer in the morning. We estimated that ~ 1.7–4.0 ppbv of ClNO2 would exist in the residual layer in order to maintain the observed morning ClNO2 peaks at the surface site. Observation-based box model analysis show that photolysis of ClNO2 produced chlorine radical with a rate up to 1.12 ppbv h−1, accounting for 10–30 % of primary ROx production in the morning hours. The perturbation in total radical production leads to an increase of integrated daytime net ozone production by 3 % (4.3 ppbv) on average, and with a larger increase of 13 % (11 ppbv) in megacity outflow that was characterized with higher ClNO2 and relatively lower OVOC to NMHC ratio.

scholarly journals Significant concentrations of nitryl chloride sustained in the morning: investigations of the causes and impacts on ozone production in a polluted region of northern China

2016 ◽  
Vol 16 (23) ◽  
pp. 14959-14977 ◽  
Author(s):  
Yee Jun Tham ◽  
Zhe Wang ◽  
Qinyi Li ◽  
Hui Yun ◽  
Weihao Wang ◽  
...  
Keyword(s):  
Inversion Layer ◽  
Northern China ◽  
Residual Layer ◽  
Ozone Production ◽  
Rural Site ◽  
Ionization Mass ◽  
Dinitrogen Pentoxide ◽  
Mixing Ratios ◽  
Nitryl Chloride ◽  
Nocturnal Inversion

Abstract. Nitryl chloride (ClNO2) is a dominant source of chlorine radical in polluted environment, and can significantly affect the atmospheric oxidative chemistry. However, the abundance of ClNO2 and its exact role are not fully understood under different environmental conditions. During the summer of 2014, we deployed a chemical ionization mass spectrometer to measure ClNO2 and dinitrogen pentoxide (N2O5) at a rural site in the polluted North China Plain. Elevated mixing ratios of ClNO2 (> 350 pptv) were observed at most of the nights with low levels of N2O5 (< 200 pptv). The highest ClNO2 mixing ratio of 2070 pptv (1 min average) was observed in a plume from a megacity (Tianjin), and was characterized with a faster N2O5 heterogeneous loss rate and ClNO2 production rate compared to average conditions. The abundant ClNO2 concentration kept increasing even after sunrise, and reached a peak 4 h later. Such highly sustained ClNO2 peaks after sunrise are discrepant from the previously observed typical diurnal pattern. Meteorological and chemical analysis shows that the sustained ClNO2 morning peaks are caused by significant ClNO2 production in the residual layer at night followed by downward mixing after breakup of the nocturnal inversion layer in the morning. We estimated that  ∼  1.7–4.0 ppbv of ClNO2 would exist in the residual layer in order to maintain the observed morning ClNO2 peaks at the surface site. Observation-based box model analysis show that photolysis of ClNO2 produced chlorine radical with a rate up to 1.12 ppbv h−1, accounting for 10–30 % of primary ROx production in the morning hours. The perturbation in total radical production leads to an increase of integrated daytime net ozone production by 3 % (4.3 ppbv) on average, and with a larger increase of 13 % (11 ppbv) in megacity outflow that was characterized with higher ClNO2 and a relatively lower oxygenated hydrocarbon (OVOC) to non-methane hydrocarbon (NMHC) ratio.

scholarly journals Urban inland wintertime N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> influenced by snow-covered ground, air turbulence, and precipitation

2021 ◽  
Author(s):  
Kathryn D. Kulju ◽  
Stephen M. McNamara ◽  
Qianjie Chen ◽  
Jacinta Edebeli ◽  
Jose D. Fuentes ◽  
...  
Keyword(s):  
Ground Cover ◽  
Atmospheric Particulate Matter ◽  
Ionization Mass ◽  
Bare Ground ◽  
Near Surface ◽  
Dinitrogen Pentoxide ◽  
Nitryl Chloride ◽  
Air Turbulence ◽  
Chlorine Radicals ◽  
Wet Scavenging

Abstract. The atmospheric multiphase reaction of dinitrogen pentoxide (N2O5) with chloride-containing aerosol particles produces nitryl chloride (ClNO2), which has been observed across the globe. The photolysis of ClNO2 produces chlorine radicals and nitrogen dioxide (NO2), which alter pollutant fates and air quality. However, the effects of local meteorology on near-surface ClNO2 production are not yet well understood, as most observational and modeling studies focus on periods of clear conditions. During a field campaign in Kalamazoo, Michigan from January–February 2018, N2O5 and ClNO2 were measured using chemical ionization mass spectrometry, with simultaneous measurements of atmospheric particulate matter and meteorological parameters. We examine the impacts of atmospheric turbulence, precipitation (snow, rain) and fog, and ground cover (snow-covered and bare ground) on the abundances of ClNO2 and N2O5. N2O5 mole ratios were lowest during periods of lower turbulence and were not statistically significantly different between snow-covered and bare ground. In contrast, ClNO2 mole ratios were highest, on average, over snow-covered ground, due to saline snowpack ClNO2 production. Both N2O5 and ClNO2 mole ratios were lowest, on average, during rainfall and fog because of scavenging, with N2O5 scavenging by fog droplets likely contributing to observed increased particulate nitrate concentrations. These observations, specifically those during active precipitation and with snow-covered ground, highlight important processes, including N2O5 and ClNO2 wet scavenging, fog nitrate production, and snowpack ClNO2 production, that govern the variability in observed atmospheric chlorine and nitrogen chemistry and are missed when considering only clear conditions.

scholarly journals High concentrations of N<sub>2</sub>O<sub>5</sub> and NO<sub>3</sub> observed in daytime with a TD-CIMS: chemical interference or a real atmospheric phenomenon?

2013 ◽  
Vol 6 (4) ◽  
pp. 7473-7504
Author(s):  
X. Wang ◽  
T. Wang ◽  
C. Yan ◽  
Y. J. Tham ◽  
L. Xue ◽  
...  
Keyword(s):  
Hong Kong ◽  
Atmospheric Chemistry ◽  
Thermal Dissociation ◽  
Measurement Techniques ◽  
Urban Site ◽  
Ionization Mass ◽  
Dinitrogen Pentoxide ◽  
Mixing Ratios ◽  
High Concentrations ◽  
Interference Tests

Abstract. Dinitrogen pentoxide (N2O5) and the nitrate radical (NO3) play important roles in atmospheric chemistry, yet accurate measurements of their concentrations remain challenging. A thermal dissociation chemical ionization mass spectrometer (TD-CIMS) was deployed to an urban site in Hong Kong to measure the sum of N2O5 and NO3 in autumn 2010. To our surprise, very high concentrations of N2O5 + NO3 were frequently observed in daytime, with mixing ratios in the range of 200–1000 pptv. To investigate this unusual phenomenon, various interference tests and measurements with different instrument configuration were conducted. It was found that peroxy acetyl nitrate (PAN) contributed to measurable signals at 62 amu, and more importantly, this interference increased significantly with co-existence of NO2. Nitric acid (HNO3), on the other hand, had little interference to the detection of N2O5/NO3 via the NO3− ion in our TD-CIMS. According to the test results, the interference from PAN and NO2 could have contributed to 30–50% of the average daytime (12:00–16:00 LT) N2O5 + NO3 signal at our site. However, evidence exists for the presence of elevated daytime N2O5, in addition to the daytime signal at 62 amu. This includes: (1) daytime N2O5 measured via the I(N2O5)− cluster ion with an unheated inlet, which subjects to minimum interferences, and (2) observation of elevated daytime ClNO2 (a product of N2O5 hydrolysis) during a follow-up study. In view of the difficulty in accurately quantifying the contribution from the interferences of PAN and NO2 and un-tested potential interfering chemicals in the real atmosphere, we caution the use of 62 amu in the TD-CIMS for measuring ambient N2O5 in a high NOx environment like Hong Kong. Additional studies are needed to re-examine the daytime issue using other measurement techniques.

Ubiquity of ClNO2 in the urban boundary layer of Calgary, Alberta, Canada

2016 ◽  
Vol 94 (4) ◽  
pp. 414-423 ◽  
Author(s):  
Levi H. Mielke ◽  
Amanda Furgeson ◽  
Charles A. Odame-Ankrah ◽  
Hans D. Osthoff
Keyword(s):  
Chlorine Atom ◽  
Urban Environments ◽  
Heterogeneous Reactions ◽  
Ionization Mass ◽  
Mixing Ratios ◽  
Nitryl Chloride ◽  
Reservoir Species ◽  
Intermittent Measurements ◽  
Oxidation Of No

The role of nitryl chloride (ClNO2) as a nocturnal nitrogen oxide reservoir species and chlorine atom precursor is well established for polluted coastal areas, but its role at midcontinental locations is less clear. In this paper, intermittent measurements over the course of several seasons of ClNO2 mixing ratios by iodide ion chemical ionization mass spectrometry in Calgary, Alberta, Canada, are presented. Mixing ratios were highly variable between nights and seasons and depended on the abundances of precursors and meteorological conditions. The lowest ClNO2 mixing ratios (nocturnal maximum of 30 parts per trillion by volume (pptv)) were observed in the summer, rationalized by losses of the nitrate radical (NO3) that were more efficient than in the other months. Higher ClNO2 mixing ratios (up to 330 pptv) were observed in the winter and spring months but varied between nights. In the fall, ClNO2 mixing ratios increased from night to night following the application of salt to roads. The ClNO2 yield relative to the amount of NO3 produced from oxidation of NO2 by O3 ranged from 0.1% to 4.5% (10th and 90th percentiles, median 1.0%). The ClNO2 yield relative to N2O5 consumed by heterogeneous reactions was estimated using a time-integrated box model and ranged from 0.5% to 12.1% (10th and 90th percentiles, median 3.4%). The ubiquity of ClNO2 implies that the chlorine atom needs to be considered as an oxidant in high-latitude urban environments in winter.

scholarly journals Efficient N<sub>2</sub>O<sub>5</sub> uptake and NO<sub>3</sub> oxidation in the outflow of urban Beijing

2018 ◽  
Vol 18 (13) ◽  
pp. 9705-9721 ◽  
Author(s):  
Haichao Wang ◽  
Keding Lu ◽  
Song Guo ◽  
Zhijun Wu ◽  
Dongjie Shang ◽  
...  
Keyword(s):  
North China Plain ◽  
North China ◽  
Field Studies ◽  
Organic Nitrate ◽  
Air Masses ◽  
Dinitrogen Pentoxide ◽  
Nitryl Chloride ◽  
The North ◽  
Heterogeneous Processes ◽  
Volatile Organic

Abstract. Nocturnal reactive nitrogen compounds play an important role in regional air pollution. Here we present the measurements of dinitrogen pentoxide (N2O5) associated with nitryl chloride (ClNO2) and particulate nitrate (pNO3-) at a suburban site of Beijing in the summer of 2016. High levels of N2O5 and ClNO2 were observed in the outflow of the urban Beijing air masses, with 1 min average maxima of 937 and 2900 pptv, respectively. The N2O5 uptake coefficients, γ, and ClNO2 yield, f, were experimentally determined from the observed parameters. The N2O5 uptake coefficient ranged from 0.012 to 0.055, with an average of 0.034 ± 0.018, which is in the upper range of previous field studies reported in North America and Europe but is a moderate value in the North China Plain (NCP), which reflects efficient N2O5 heterogeneous processes in Beijing. The ClNO2 yield exhibited high variability, with a range of 0.50 to unity and an average of 0.73 ± 0.25. The concentration of the nitrate radical (NO3) was calculated assuming that the thermal equilibrium between NO3 and N2O5 was maintained. In NOx-rich air masses, the oxidation of nocturnal biogenic volatile organic compounds (BVOCs) was dominated by NO3 rather than O3. The production rate of organic nitrate (ON) via NO3 + BVOCs was significant, with an average of 0.10 ± 0.07 ppbv h−1. We highlight the importance of NO3 oxidation of VOCs in the formation of ON and subsequent secondary organic aerosols in summer in Beijing.

scholarly journals Detection of dimethylamine in the low pptv range using nitrate chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometry

2016 ◽  
Vol 9 (5) ◽  
pp. 2135-2145 ◽  
Author(s):  
Mario Simon ◽  
Martin Heinritzi ◽  
Stephan Herzog ◽  
Markus Leiminger ◽  
Federico Bianchi ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Atmospheric Pressure ◽  
Chemical Ionization ◽  
Integration Time ◽  
Ionization Mass ◽  
Mixing Ratios ◽  
Highly Sensitive ◽  
Volatile Organic ◽  
Cluster Ion

Abstract. Amines are potentially important for atmospheric new particle formation, but their concentrations are usually low with typical mixing ratios in the pptv range or even smaller. Therefore, the demand for highly sensitive gas-phase amine measurements has emerged in the last several years. Nitrate chemical ionization mass spectrometry (CIMS) is routinely used for the measurement of gas-phase sulfuric acid in the sub-pptv range. Furthermore, extremely low volatile organic compounds (ELVOCs) can be detected with a nitrate CIMS. In this study we demonstrate that a nitrate CIMS can also be used for the sensitive measurement of dimethylamine (DMA, (CH3)2NH) using the NO3−•(HNO3)1 − 2• (DMA) cluster ion signal. Calibration measurements were made at the CLOUD chamber during two different measurement campaigns. Good linearity between 0 and  ∼  120 pptv of DMA as well as a sub-pptv detection limit of 0.7 pptv for a 10 min integration time are demonstrated at 278 K and 38 % RH.

scholarly journals Efficient N<sub>2</sub>O<sub>5</sub> Uptake and NO<sub>3</sub> Oxidation in the Outflow of Urban Beijing

2018 ◽  
Author(s):  
Haichao Wang ◽  
Keding Lu ◽  
Song Guo ◽  
Zhijun Wu ◽  
Dongjie Shang ◽  
...  
Keyword(s):  
Field Studies ◽  
Organic Nitrates ◽  
Air Masses ◽  
Dinitrogen Pentoxide ◽  
Nitryl Chloride ◽  
The North ◽  
Initial Reduction ◽  
Heterogeneous Processes ◽  
Volatile Organic ◽  
Ratio Condition

Abstract. Nocturnal reactive nitrogen compounds are important for understanding regional air pollution. Here we present the measurements of dinitrogen pentoxide (N2O5) associated with nitryl chloride (ClNO2) and particulate nitrate (pNO3−) in a suburban site of Beijing in the summer of 2016. High levels of N2O5 and ClNO2 were observed in the outflow of the urban Beijing air masses, with 1-min average maxima of 937 pptv and 2.9 ppbv, respectively. The N2O5 uptake coefficients, γ, and ClNO2 yield, f, were experimentally determined from the observed parameters. The N2O5 uptake coefficient ranged from 0.012 to 0.055, with an average of 0.034 ± 0.018, which is in the upper range of previous field studies reported in North America and Europe but is a moderate value in the North China Plain (NCP), which reflects efficient N2O5 heterogeneous processes in Beijing. The ClNO2 yield exhibited high variability, with a range of 0.50 to unity and an average of 0.73 ± 0.25. The nighttime nitrate radical (NO3) was calculated assuming that the thermal equilibrium between NO3 and N2O5 was maintained. In NO2-rich air masses, the oxidation of nocturnal biogenic volatile organic compounds (BVOCs) was dominated by NO3 rather than O2. The production rate of organic nitrates (ONs) via NO2+BVOCs was significant, with an average of 0.11 ± 0.09 ppbv h−1. We highlight the importance of NO2 oxidation of VOCs in the formation of ONs and subsequent secondary organic aerosols in summer in Beijing. The capacities of BVOCs oxidation and ONs formation are maximized and independent of NOx under a high NOx/BVOCs ratio condition (>10), which indicates that the initial reduction of the NOx emission cannot help reduce the nocturnal formation of ONs.

scholarly journals Observation and modelling of HO<sub>x</sub> radicals in a boreal forest

2014 ◽  
Vol 14 (16) ◽  
pp. 8723-8747 ◽  
Author(s):  
K. Hens ◽  
A. Novelli ◽  
M. Martinez ◽  
J. Auld ◽  
R. Axinte ◽  
...  
Keyword(s):  
Steady State ◽  
Boreal Forest ◽  
Hydroxyl Radicals ◽  
Chemical Ionization ◽  
Box Model ◽  
Ionization Mass ◽  
Organic Precursor ◽  
Mixing Ratios ◽  
Volatile Organic ◽  
State Assumption

Abstract. Measurements of OH and HO2 radicals were conducted in a pine-dominated forest in southern Finland during the HUMPPA-COPEC-2010 (Hyytiälä United Measurements of Photochemistry and Particles in Air – Comprehensive Organic Precursor Emission and Concentration study) field campaign in summer 2010. Simultaneous side-by-side measurements of hydroxyl radicals were conducted with two instruments using chemical ionization mass spectrometry (CIMS) and laser-induced fluorescence (LIF), indicating small systematic disagreement, OHLIF / OHCIMS = (1.31 ± 0.14). Subsequently, the LIF instrument was moved to the top of a 20 m tower, just above the canopy, to investigate the radical chemistry at the ecosystem–atmosphere interface. Comprehensive measurements including observations of many volatile organic compounds (VOCs) and the total OH reactivity were conducted and analysed using steady-state calculations as well as an observationally constrained box model. Production rates of OH calculated from measured OH precursors are consistent with those derived from the steady-state assumption and measured total OH loss under conditions of moderate OH reactivity. The primary photolytic sources of OH contribute up to one-third to the total OH production. OH recycling, which occurs mainly by HO2 reacting with NO and O3, dominates the total hydroxyl radical production in this boreal forest. Box model simulations agree with measurements for hydroxyl radicals (OHmod. / OHobs. = 1.00 ± 0.16), while HO2 mixing ratios are significantly under-predicted (HO2mod. / HO2obs. = 0.3 ± 0.2), and simulated OH reactivity does not match the observed OH reactivity. The simultaneous under-prediction of HO2 and OH reactivity in periods in which OH concentrations were simulated realistically suggests that the missing OH reactivity is an unaccounted-for source of HO2. Detailed analysis of the HOx production, loss, and recycling pathways suggests that in periods of high total OH reactivity there are additional recycling processes forming OH directly, not via reaction of HO2 with NO or O3, or unaccounted-for primary HOx sources. Under conditions of moderate observed OH reactivity and high actinic flux, an additional RO2 source of approximately 1 × 106 molec cm−3 s−1 would be required to close the radical budget. Nevertheless, a major fraction of the OH recycling occurs via the reaction of HO2 with NO and O3 in this terpene-dominated environment.

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