scholarly journals Supplementary material to "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):  
Atmospheric Oxidation ◽  
Ozone Pollution ◽  
Southeast China ◽  
Oxidation Capacity ◽  
Coastal City ◽  
Supplementary Material ◽  
Pollution Mechanism

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 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 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 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.

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