scholarly journals Atmospheric oxidation capacity and ozone pollution mechanism in a coastal city of Southeast China: Analysis of a typical photochemical episode by Observation-Based Model

2021 ◽  
Author(s):  
Taotao Liu ◽  
Youwei Hong ◽  
Mengren Li ◽  
Lingling Xu ◽  
Jinsheng Chen ◽  
...  
Keyword(s):  
Chemical Mechanism ◽  
Atmospheric Oxidation ◽  
Limiting Factor ◽  
Ozone Pollution ◽  
Regional Transport ◽  
Southeast China ◽  
Oxidation Capacity ◽  
Coastal City ◽  
Regional Collaboration ◽  
Pollution Mechanism

Abstract. A typical multi-day ozone (O3) pollution event was chosen to explore the atmospheric oxidation capacity (AOC), OH reactivity, radical chemistry, and O3 pollution mechanism in a coastal city of Southeast China, with an Observation-Based Model coupled to the Master Chemical Mechanism (OBM-MCM). The hydroxyl radical (OH) was the predominant oxidant (91±23 %) for daytime AOC, while NO3 radical played an important role for AOC during the nighttime (64±11 %). Oxygenated volatile organic compounds (OVOCs, 30±8 %), NO2 (29±8 %) and CO (25±5 %) were the dominant contributors to OH reactivity, accelerating the production of O3 and recycling of ROx radicals (ROx=OH+HO2+RO2). Photolysis of nitrous acid (HONO, 33±14 %), O3 (25±13 %), formaldehyde (HCHO, 20±5 %), and other OVOCs (17±2 %) were the important primary sources of ROx radicals, which played initiation roles in atmospheric oxidation processes. O3 formation was VOC-sensitive, and controlling emissions of aromatics, alkenes, and long-chain alkanes were benefit for ozone pollution mitigation. Combined with regional transport analysis, the reasons for this O3 episode were the accumulation of local photochemical production and regional transport. The results of sensitivity analysis showed that VOCs were the limiting factor of radical recycling and O3 formation, and the 5 % reduction of O3 would be achieved by decreasing 20 % anthropogenic VOCs. The findings of this study have significant guidance for emission reduction and regional collaboration on future photochemical pollution control in the relatively clean coastal cities of China and similar countries.

scholarly journals Observationally constrained modeling of atmospheric oxidation capacity and photochemical reactivity in Shanghai, China

2020 ◽  
Vol 20 (3) ◽  
pp. 1217-1232 ◽  
Author(s):  
Jian Zhu ◽  
Shanshan Wang ◽  
Hongli Wang ◽  
Shengao Jing ◽  
Shengrong Lou ◽  
...  
Keyword(s):  
Air Quality ◽  
Chain Length ◽  
Ambient Air ◽  
Chemical Mechanism ◽  
Atmospheric Oxidation ◽  
Oh Radicals ◽  
Ozone Pollution ◽  
Oxidation Capacity ◽  
High Level ◽  
Ozone Levels

Abstract. An observation-based model coupled to the Master Chemical Mechanism (V3.3.1) and constrained by a full suite of observations was developed to study atmospheric oxidation capacity (AOC), OH reactivity, OH chain length and HOx (=OH+HO2) budget for three different ozone (O3) concentration levels in Shanghai, China. Five months of observations from 1 May to 30 September 2018 showed that the air quality level is lightly polluted or worse (Ambient Air Quality Index, AQI, of > 100) for 12 d, of which ozone is the primary pollutant for 10 d, indicating ozone pollution was the main air quality challenge in Shanghai during summer of 2018. The levels of ozone and its precursors, as well as meteorological parameters, revealed the significant differences among different ozone levels, indicating that the high level of precursors is the precondition of ozone pollution, and strong radiation is an essential driving force. By increasing the input JNO2 value by 40 %, the simulated O3 level increased by 30 %–40 % correspondingly under the same level of precursors. The simulation results show that AOC, dominated by reactions involving OH radicals during the daytime, has a positive correlation with ozone levels. The reactions with non-methane volatile organic compounds (NMVOCs; 30 %–36 %), carbon monoxide (CO; 26 %–31 %) and nitrogen dioxide (NO2; 21 %–29 %) dominated the OH reactivity under different ozone levels in Shanghai. Among the NMVOCs, alkenes and oxygenated VOCs (OVOCs) played a key role in OH reactivity, defined as the inverse of the OH lifetime. A longer OH chain length was found in clean conditions primarily due to low NO2 in the atmosphere. The high level of radical precursors (e.g., O3, HONO and OVOCs) promotes the production and cycling of HOx, and the daytime HOx primary source shifted from HONO photolysis in the morning to O3 photolysis in the afternoon. For the sinks of radicals, the reaction with NO2 dominated radical termination during the morning rush hour, while the reactions of radical–radical also contributed to the sinks of HOx in the afternoon. Furthermore, the top four species contributing to ozone formation potential (OFP) were HCHO, toluene, ethylene and m/p-xylene. The concentration ratio (∼23 %) of these four species to total NMVOCs is not proportional to their contribution (∼55 %) to OFP, implying that controlling key VOC species emission is more effective than limiting the total concentration of VOC in preventing and controlling ozone pollution.

Budget of nitrous acid (HONO) and its impacts on atmospheric oxidation capacity at an urban site in Guangzhou of China

2021 ◽  
Author(s):  
Yihang Yu ◽  
Peng Cheng ◽  
Huirong Li ◽  
Wenda Yang ◽  
Baobin Han ◽  
...  
Keyword(s):  
Nitrous Acid ◽  
Emission Rate ◽  
Chemical Mechanism ◽  
Atmospheric Oxidation ◽  
Urban Site ◽  
Homogeneous Reaction ◽  
Pearl River Delta Region ◽  
Oxidation Capacity ◽  
High Concentrations ◽  
The Impact

<p>Nitrous acid (HONO) can produce hydroxyl radicals (OH) by photolysis and plays an important role in atmospheric photochemistry. Over the years, high concentrations of HONO have been found in the Pearl River Delta region (PRD), which may be one of the reasons for the high atmospheric oxidation capacity. A comprehensive atmospheric observation was conducted at an urban site in Guangzhou from 27 September to 9 November 2018. During the period, HONO ranged from 0.02 to 4.43 ppbv with an average of 0.74±0.70 ppbv. The combustion emission ratio (HONO/NOx) of 0.9±0.4% was derived from 11 fresh plumes. The primary emission rate of HONO during night was calculated with the emission source inventory data to be between 0.04±0.02 and 0.30±0.15 ppbv/h. And the HONO produced by the homogeneous reaction of OH+NO at night was 0.26±0.08 ppbv/h, which can be seemed as secondary results from primary emission. They were both much higher than the increase rate of HONO (0.02 ppbv/h) during night. Soil emission rate of HONO at night was calculated to be 0.019±0.0003 ppbv/h. Deposition was the dominant removal process of HONO during night, and a deposition rate of at least 2.5 cm/s is required to balance the direct emissions and OH+NO reaction. Correlation analysis shows that NH<sub>3</sub> and relative humidity (RH) may participate in the heterogeneous transformation from NO<sub>2</sub> to HONO during night. In the daytime, the average primary emission P<sub>emis</sub> was 0.12±0.01 ppbv/h, and the homogeneous reaction P<sub>OH+NO</sub> was 0.79±0.61 ppbv/h, which was even larger than the unknown sources P<sub>Unknown</sub> (0.65±0.46 ppbv/h). The results showed that the direct and indirect contributions of primary emission to HONO are great at the site, both during daytime and nighttime. Similar to previous studies, P<sub>Unknown</sub> was suggested to be related to the photo-enhanced reaction of NO<sub>2</sub>. The mean OH production rates by photolysis of HONO and O<sub>3</sub> were 3.7×10<sup>6</sup> cm<sup>-3</sup>·s<sup>-1</sup> and 4.9×10<sup>6</sup> cm<sup>-3</sup>·s<sup>-1</sup>, respectively. We further studied the impact of HONO on the atmospheric oxidation by a Master Chemical Mechanism (MCM) box model. When constraining observed HONO in the model, OH and O<sub>3 </sub>increased 59% and 68.8% respectively, showing a remarkable contribution of HONO to the atmospheric oxidation of Guangzhou.</p><p> </p>

scholarly journals Atmospheric oxidation capacity in Chinese megacities during photochemical polluted season: radical budget and secondary pollutants formation

2018 ◽  
Author(s):  
Zhaofeng Tan ◽  
Keding Lu ◽  
Meiqing Jiang ◽  
Rong Su ◽  
Hongli Wang ◽  
...  
Keyword(s):  
Fine Particle ◽  
Fine Particles ◽  
Nox Reduction ◽  
Ozone Production ◽  
Atmospheric Oxidation ◽  
Ozone Pollution ◽  
Oxidation Capacity ◽  
Radical Chemistry ◽  
Budget Analysis ◽  
Secondary Pollutants

Abstract. Atmospheric oxidation capacity is the core of converting fresh-emitted substances to secondary pollutants. In this study, we present the in-situ measurements at four Chinese megacities (Beijing, Shanghai, Guangzhou, and Chongqing) in China during photochemical polluted seasons. The atmospheric oxidation capacity is evaluated using an observational-based model with the input of radical chemistry precursor measurements. The radical budget analysis illustrates the importance of HONO and HCHO photolysis, which contribute nearly half of the total radical primary sources. The radical propagation is efficient due to abundant of NO in the urban environments. Hence, the production rate of secondary pollutants, i.e. ozone and fine particle precursors (H2SO4, HNO3, and ELVOCs) is fast resulting in secondary air pollution. The ozone budget demonstrates that strong ozone production occurs in the urban area which results in fast ozone concentration increase locally and further transported to downwind areas. On the other hand, the O3-NOx-VOC sensitivity tests show that ozone production is VOC-limited, among which alkenes and aromatics should be first mitigated for ozone pollution control in the presented four megacities. However, NOx emission control will lead to more server ozone pollution due to the drawback-effect of NOx reduction. For fine particle pollution, the role of HNO3−NO3− partitioning system is investigated with a thermal dynamic model (ISORROPIA2) due to the importance of particulate nitrate during photochemical polluted seasons. The strong nitrate acid production converts efficiently to nitrate particles due to high RH and ammonium-rich conditions during photochemical polluted seasons. This study highlights the efficient radical chemistry maintains the atmospheric oxidation capacity in Chinese megacities, which results in secondary pollutions characterized by ozone and fine particles.

scholarly journals Observationally constrained modelling of atmospheric oxidation capacity and photochemical reactivity in Shanghai, China

2019 ◽  
Author(s):  
Jian Zhu ◽  
Shanshan Wang ◽  
Hongli Wang ◽  
Shengao Jing ◽  
Shengrong Lou ◽  
...  
Keyword(s):  
Air Quality ◽  
Chain Length ◽  
Chemical Mechanism ◽  
Atmospheric Oxidation ◽  
Photochemical Reactivity ◽  
Oxidation Capacity ◽  
Master Chemical Mechanism ◽  
Primary Pollutant ◽  
Concentration Levels

Abstract. An observation-based model coupled to the Master Chemical Mechanism (V3.3.1) and constrained by a full suite of observations was developed to study atmospheric oxidation capacity (AOC), OH reactivity, OH chain length, and HOx (= OH + HO2) budget for three different ozone (O3) concentration levels in Shanghai, China. Five months of observation from 1 May to 30 September 2018 showed that 10 days with ozone as the primary pollutant occurred and the days with good air quality (AQI 

scholarly journals Daytime atmospheric oxidation capacity in four Chinese megacities during the photochemically polluted season: a case study based on box model simulation

2019 ◽  
Vol 19 (6) ◽  
pp. 3493-3513 ◽  
Author(s):  
Zhaofeng Tan ◽  
Keding Lu ◽  
Meiqing Jiang ◽  
Rong Su ◽  
Hongli Wang ◽  
...  
Keyword(s):  
Urban Areas ◽  
Fine Particle ◽  
Fine Particles ◽  
Model Simulation ◽  
Ozone Production ◽  
Atmospheric Oxidation ◽  
Ozone Pollution ◽  
Oxidation Capacity ◽  
Radical Chemistry ◽  
Budget Analysis

Abstract. Atmospheric oxidation capacity is the basis for converting freshly emitted substances into secondary products and is dominated by reactions involving hydroxyl radicals (OH) during daytime. In this study, we present in situ measurements of ROx radical (hydroxy OH, hydroperoxy HO2, and organic peroxy RO2) precursors and products; the measurements are carried out in four Chinese megacities (Beijing, Shanghai, Guangzhou, and Chongqing) during photochemically polluted seasons. The atmospheric oxidation capacity is evaluated using an observation-based model and radical chemistry precursor measurements as input. The radical budget analysis illustrates the importance of HONO and HCHO photolysis, which account for ∼50 % of the total primary radical sources. The radical propagation is efficient due to abundant NO in urban environments. Hence, the production rate of secondary pollutants, that is, ozone (and fine-particle precursors (H2SO4, HNO3, and extremely low volatility organic compounds, ELVOCs) is rapid, resulting in secondary air pollution. The ozone budget demonstrates its high production in urban areas; also, its rapid transport to downwind areas results in rapid increase in local ozone concentrations. The O3–NOx–VOC (volatile organic compound) sensitivity tests show that ozone production is VOC-limited and that alkenes and aromatics should be mitigated first for ozone pollution control in the four studied megacities. In contrast, NOx emission control (that is, a decrease in NOx) leads to more severe ozone pollution. With respect to fine-particle pollution, the role of the HNO3–NO3 partitioning system is investigated using a thermal dynamic model (ISORROPIA 2). Under high relative humidity (RH) and ammonia-rich conditions, nitric acid converts into nitrates. This study highlights the efficient radical chemistry that maintains the atmospheric oxidation capacity in Chinese megacities and results in secondary pollution characterized by ozone and fine particles.

scholarly journals Budget of nitrous acid (HONO) and its impacts on atmospheric oxidation capacity at an urban site in the fall season of Guangzhou, China

2021 ◽  
Author(s):  
Yihang Yu ◽  
Peng Cheng ◽  
Huirong Li ◽  
Wenda Yang ◽  
Baobin Han ◽  
...  
Keyword(s):  
Nitrous Acid ◽  
Deposition Velocity ◽  
Chemical Mechanism ◽  
Atmospheric Oxidation ◽  
Urban Site ◽  
Enhancement Effect ◽  
Homogeneous Reaction ◽  
Pearl River Delta Region ◽  
Fall Season ◽  
Oxidation Capacity

Abstract. Nitrous acid (HONO) can produce hydroxyl radicals (OH) by photolysis and plays an important role in atmospheric photochemistry. Over the years, high concentrations of HONO have been observed in the Pearl River Delta region (PRD) of China, which may be one reason for the elevated atmospheric oxidation capacity. A comprehensive atmospheric observation campaign was conducted at an urban site in Guangzhou from 27 September to 9 November 2018. During the period, HONO was measured from 0.02 to 4.43 ppbv with an average of 0.74 ± 0.70 ppbv. The emission ratios (HONO/NOx) of 0.9 ± 0.4 % were derived from 11 fresh plumes. The primary emission rates of HONO at night were calculated to be between 0.04 ± 0.02 ppbv h−1 and 0.30 ± 0.15 ppbv h−1 based on a high-resolution emission inventory. The HONO formation rate by the homogeneous reaction of OH + NO at night was 0.26 ± 0.08 ppbv h−1, which can be seen as secondary results from primary emission. They were both much higher than the increase rate of HONO (0.02 ppbv h−1) during night. Soil emission rate of HONO at night was calculated to be 0.019 ± 0.001 ppbv h−1. Assuming dry deposition as the dominant removal process of HONO at night, and a deposition velocity of at least ~2.5 cm s−1 is required to balance the direct emissions and OH + NO reaction. Correlation analysis shows that NH3 and relative humidity (RH) may participate in the heterogeneous transformation from NO2 to HONO at night. In the daytime, the average primary emission Pemis was 0.12 ± 0.01 ppbv h−1, and the homogeneous reaction POH + NO was 0.79 ± 0.61 ppbv h−1, larger than the unknown sources PUnknown (0.65 ± 0.46 ppbv h−1). These results suggest primary emissions as a key factor affecting HONO at our site, both during daytime and nighttime. Similar to previous studies, the daytime unknown source of HONO, PUnknown, appeared to be related to the photo-enhanced conversion of NO2. The daytime average OH production rates by photolysis of HONO was 3.7 × 106 cm−3 s−1, lower than that from O1D + H2O at 4.9 × 106 cm−3 s−1. Simulations of OH and O3 with the Master Chemical Mechanism (MCM) box model suggested strong enhancement effect of HONO on OH and O3 by 59 % and 68.8 %, respectively, showing a remarkable contribution of HONO to the atmospheric oxidation in the fall season of Guangzhou.

scholarly journals Hydroxyl radicals in the tropical troposphere over the Suriname rainforest: comparison of measurements with the box model MECCA

2008 ◽  
Vol 8 (4) ◽  
pp. 15239-15289 ◽  
Author(s):  
D. Kubistin ◽  
H. Harder ◽  
M. Martinez ◽  
M. Rudolf ◽  
R. Sander ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Tropical Rainforest ◽  
Source Region ◽  
Degradation Process ◽  
Reaction Scheme ◽  
Box Model ◽  
Chemical Mechanism ◽  
Similar Amount ◽  
Oxidation Capacity ◽  
Mixing Ratios

Abstract. As a major source region of the hydroxyl radical OH, the Tropics largely control the oxidation capacity of the atmosphere on a global scale. However, emissions of hydrocarbons from the tropical rainforest that react rapidly with OH can potentially deplete the amount of OH and thereby reduce the oxidation capacity. The airborne GABRIEL field campaign in equatorial South America (Suriname) in October 2005 investigated the influence of the tropical rainforest on the HOx budget (HOx=OH+HO2). The first observations of OH and HO2 over a tropical rainforest are compared to steady state concentrations calculated with the atmospheric chemistry box model MECCA. The important precursors and sinks for HOx chemistry, measured during the campaign, are used as constraining parameters for the simulation of OH and HO2. Significant underestimations of HOx are found by the model over land during the afternoon, with mean ratios of observation to model of 12.2±3.5 and 4.1±1.4 for OH and HO2, respectively. The discrepancy between measurements and simulation results is correlated to the abundance of isoprene. While for low isoprene mixing ratios (above ocean or at altitudes >3 km), observation and simulation agree fairly well, for mixing ratios >200 pptV (<3 km over the rainforest) the model tends to underestimate the HOx observations as a function of isoprene. Box model simulations have been performed with the condensed chemical mechanism of MECCA and with the detailed isoprene reaction scheme of MCM, resulting in similar results for HOx concentrations. Simulations with constrained HO2 concentrations show that the conversion from HO2 to OH in the model is too low. However, by neglecting the isoprene chemistry in the model, observations and simulations agree much better. An OH source similar to the strength of the OH sink via isoprene chemistry is needed in the model to resolve the discrepancy. A possible explanation is that the oxidation of isoprene by OH not only dominates the removal of OH but also produces it in a similar amount. Several additional reactions which directly produce OH have been implemented into the box model, suggesting that upper limits in producing OH are still not able to reproduce the observations (improvement by factors of ≈2.4 and ≈2 for OH and HO2, respectively). We determine that OH has to be recycled to 94% instead of the simulated 38% to match the observations, which is most likely to happen in the isoprene degradation process, otherwise additional sources are required.

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