Ozone Pollution Episodes Research Articles

Insight into ozone profile climatology over northeast China from aircraft measurement and numerical simulation

Tropospheric ozone is a major pollutant that can harm human health, animals and plants. With a rapid development in Northeast China, ozone pollution has become an increasingly serious environmental challenge. To study the ozone distribution and the potential sources of ozone precursors in Northeast China, we analyzed vertical ozone profiles from the In-service Aircraft for a Global Observing System (IAGOS) in 2012–2014 and provided the climatological vertical structure of tropospheric ozone over Shenyang. The tropospheric ozone generally presents high in hot months, mainly due to the combined effects of the strong solar radiation and high volatile organic compounds emission in summer. While in cold months, the ozone is low because of weak solar radiation and high nitrogen oxides emission. Besides, a low-ozone center exists within lower troposphere in August, which is mainly caused by the East Asian summer monsoon prevailing in summer. To analyze the sources of ozone, typical ozone pollution episodes were studied and the results revealed the different pathways for the enhancement of ozone pollution in Shenyang: regional transport of anthropogenic emissions from North China Plain (NCP), long-range transport from Siberian biomass burning and local photochemical production. Modeling results show that the largest contribution to the surface ozone in Northeast China is local anthropogenic emissions (exceed 90%); the regional transport of NCP anthropogenic emissions contribute more to the pollutants around 2 km, and account for more than 50% pollutants during highly ozone polluted days; through long-range transport, Siberian biomass burning in the spring also have a nonnegligible effect on the near-ground ozone in Northeast China. Overall, this study provides tropospheric ozone climatology and its source attribution in Northeast China, and highlight the great importance of regional transport of anthropogenic and biomass burning emissions in ozone pollution.

Atmospheric formaldehyde, glyoxal and their relations to ozone pollution under low- and high-NOx regimes in summertime Shanghai, China

With the increasing concerns on summertime atmospheric photochemical pollution, the diagnosis and prevention of ozone pollution have been paid close attention. Both formaldehyde (HCHO) and glyoxal (CHOCHO) are ubiquitous oxidation intermediates of volatile organic compounds (VOCs). The ratio of glyoxal to formaldehyde (RGF) is used as a metric for VOCs emission sources. In this study, the mixing ratios of HCHO and CHOCHO have been measured by the active differential optical absorption spectroscopy (DOAS) method in the urban area of Shanghai during summertime in 2018, as well as other trace gases. The average levels of HCHO and CHOCHO are 3.31 ± 1.43 ppbv and 0.164 ± 0.073 ppbv, respectively. The similar diurnal patterns and high correlation between HCHO, CHOCHO and ozone levels implied that daytime photochemical processes are the dominant formation pathway for these trace gases. We find that with increased NOx levels, HCHO shows higher ozone formation potential relative to glyoxal. The RGF ratio increases with temperature and decreases with NO2 levels. By investigating the coupling of typical VOCs species such as acetylene, toluene and isoprene with HCHO and CHOCHO, RGF is found to be strongly impacted by the ambient VOCs profiles, suggesting that RGF should be used with caution when linking it to a given VOC precursor source. Finally, the RGF variations with ozone pollution episodes and weather processes are also discussed.

Source Apportionment of Ozone Pollution in Guangzhou: Case Study with the Application of Lagrangian Photochemical Trajectory Model

A six-day ozone pollution episode in Guangzhou in early October 2018 was analyzed with the application of a Lagrangian photochemical trajectory model to trace the sources of ozone, quantify the contributions of different regions, and evaluate the effects of emission reduction measures targeted at different emission sectors and different precursors on ozone pollution. The results showed that during the ozone pollution episode, the maximum daily 8 h ozone exceeded 160 μg·m-3 and the highest value reached 271 μg·m-3. The average concentrations of nitrogen oxides and volatile organic compounds (VOCs) were (77.7±42.8) μg·m-3 and (71.9±56.2) μg·m-3, respectively. Aromatics and alkenes were the dominant reactive VOCs, with contributions of 38% and 30% to·OH reactivity and 51% and 16% to ozone formation potential, respectively. The ozone pollution in Guangzhou during this episode was affected by three types of air masses, with the primary source regions of Guangzhou, Guangdong Province, and regions outside Guangdong Province. For all three air mass types, ozone production in these source region was controlled by VOCs. Sensitivity tests showed that, in the primary source regions, reducing the emissions of VOCs is more effective than reducing NOx in terms of reducing ozone concentrations. Under the condition of full emission reduction, regulating traffic emissions could substantially reduce ozone levels by 14.6%-21.0% in Guangzhou, which was a more significant reduction than regulating controlled industry (8.4%-15.3%), power plant (0.9%-6.2%) and residential (2.3%-4.7%) emissions. However, the traffic emission reduction is not as effective (induced ozone reduction<10%) when the emissions reduction ratio is lower than 90%. In addition, biogenic emissions in the Pearl River Delta also substantially contributed to the ozone levels under certain circumstances, as indicated by the ozone reduction up to 19% when biogenic emissions were shut off.

Long-range transport of ozone across the eastern China seas: A case study in coastal cities in southeastern China

Tropospheric ozone (O3) can be transported influenced by large-scale circulation. In this study, an ozone pollution episode in 6 cities of southeastern coastal area of China (SCA) in autumn 2017 was investigated. Compared with the typical local ozone pollution, there was no significant diurnal variations in this pollution episode, the O3 concentrations maintained a stable level of about 47 ppb continuously. The WRF-CMAQ model as well as the coupled process analysis (PA) and source apportionment modules were used to simulate the formation and transport and quantify the contributions to O3. Besides, the HYSPLIT model was used to calculate the backward trajectories arriving in the cities. We find that this pollution was mainly caused by O3 transport from the eastern China seas (ECS). Under the movement of the Mongolian high-pressure, the O3 precursors emitted from Beijing-Tianjin-Hebei (BTH), Northeast China (NEC) and Japan-Korea (JK) were transported to ECS then generated O3 through photochemical reactions. Due to the weak nitrogen oxide titration and the extremely weak ozone deposition on the water surface, O3 concentrations maintained high during the movement of air masses over ECS and finally affected SCA after long-range transport. The contributions of horizontal advections were significant basically all the day with hourly contribution about 10 ppb hr−1 and extended from surface to 500 m above the ground level. JK contributed the most, with multi-days averaged contribution about 5 ppb and peak up to 30 ppb. The contributions of BTH and NEC were comparable, with average about 2 ppb and hourly peak of 19 and 10 ppb, respectively. For the first time, this study clearly shows that the O3 precursors emitted from northern China and Japan-Korea contribute to the O3 pollution in SCA under certain weather conditions, which will help to better understand and predict the O3 pollution in that area.

Atmospheric oxidation of 1-butene initiated by OH radical: Implications for ozone and nitrous acid formations

The present study combines (i) field measurements of 1-butene over Xi'an and surrounding areas during a heavy ozone pollution episode with (ii) quantum chemical calculations on the photochemical transformation of 1-butene initiated by OH radical. The measurements show that the diurnal variation of both 1-butene and ozone exhibits a negative relationship during the sampling campaign. The concentrations of 1-butene vary from 0.04 to 0.67 ppbv, and the lowest and highest values emerge in the noon time (1 p.m.–3 p.m.) and in the night time (1 a.m.–3 a.m.). The concentrations of O3 range from 32.36 to 88.82 ppbv, and the high values appear in the noon time. Quantum chemical calculations show that the OH-addition pathways are more energetically preferable than H-abstraction channels, and the rate coefficient exhibits a negative T-dependence in the temperature range of 273–400 K. The autoxidation of peroxy radicals (RO2) formed from the addition of molecular oxygen to OH-addition products S2 and S3 leads to the formation of highly oxygenated molecules (HOMs), C4H9O5, in which the 1,5-H shift reaction is favoured. In the low-NOx regions, RO2 radicals mainly react with HO2 radical leading to hydroperoxide ROOH on both the singlet and triplet PESs, in which the triplet PES is preferable. In the high-NOx regions, RO2 radicals mainly react with NO leading to the formation of RO· + NO2, aldehyde + HONO and organic nitrate, in which the HONO formation appears to be previously unconsidered in the photochemical transformation of alkenes. The branching ratio of RO· + NO2 increases slowly with increasing temperature (from 51.3 to 52.7%), whereas aldehyde + HONO gradually decreases with the temperature rising (from 48.7 to 47.3%). The formation of organic nitrate is negligible over the temperature range of 273–400 K. These findings are expected to deepen our understanding the photochemistry oxidation of alkene under realistic atmospheric conditions.

Ozone Sensitivity Analysis and Emission Controls in Dezhou in Summer

In recent years, there have been frequent ozone pollution episodes in Dezhou, China. In the summer of 2018 (from June to August), Dezhou experienced serious ozone pollution episodes. The daily 8-hour maximum ozone concentrations exceeded the national standard for 60 days with the standard exceeding ratio of 65%. The average of daily 8-hour maximum ozone concentration was 176 μg ·m-3 over these three months, and the highest value reached was 262 μg ·m-3. In this study, the WRF-CAMx model coupled with the higher-order decoupled direct method (HDDM) was used to analyze the ozone sensitivity and emission control plans in Dezhou during this period. The results showed that ozone formation was in the strong VOC-limited regime in the urban area of Dezhou, while it was in the NOx and VOCs transition regime in suburban areas. VOCs sensitivity values (dO3_V50) were positive every day in summer, which was higher in June (18.7 μg ·m-3 in urban area, 19.7 μg ·m-3 in suburban area) and August (15.3 μg ·m-3 in urban area, 16.4 μg ·m-3 in suburban area) than in July (13.0 μg ·m-3 in urban area, 11.8 μg ·m-3 in suburban area). NOx sensitivity values (dO3_N50) were positive or negative in the urban area, and most days were positive in the suburban area, which were close to the VOCs sensitivity values. For urban areas, VOC reduction should be the priority for emission reduction plans, whereas for suburban areas, NOx：VOCs=1：1 is recommended because the reductions in NOx and VOCs emissions had the same effect on ozone pollution control.

Persistent ozone pollution episodes in North China exacerbated by regional transport

Summertime ozone (O3) concentrations over China continue to increase although the governmental Clear Air Actions have been carried out since 2013. The worst O3 pollution is confronted over North China Plain. Ozone polluted days (with observed regionally-averaged maximum daily 8-h average (MDA8) O3 concentrations exceeding 80 ppbv) in May–July in North China increased from 35 days in year 2014 to 56 days in year 2018, and persistent O3 pollution episodes that lasted for 5 days or longer (OPEs5) contributed 14.3% and 66.1% to those O3 polluted days in 2014 and 2018, respectively. Model simulations suggest that O3 transport from central eastern China (including Shandong, Henan, Jiangsu and Anhui Provinces) contributes 36% of the enhanced O3 concentrations in North China during OPEs5 relative to the seasonal mean. We find that emission control of volatile organic compounds in central eastern China is most effective to alleviate intensity of OPEs5 in North China.

Chemical Characteristics and Sources of Volatile Organic Compounds in Shanghai During an Ozone and Particulate Pollution Episode in May 2019

In the urban area of Shanghai during the complex pollution episode, ozone and PM2.5 were continuously measured from May 1 to May 28, 2019. The characterization of volatile organic compounds (VOCs) and their relationship with secondary formation were studied. The results show that in May 2019, there were four different ozone and PM2.5 pollution processes in Shanghai. The combined pollution of PM2.5 and ozone that occurred under the meteorological conditions of average temperature of approximately 26℃ and relative humidity of approximately 40% was analyzed. The photochemical consumption of VOCs was significantly positively correlated with the maximum net growth of O3 and there was a significant positive correlation between SOAP and PM2.5. The key reactive species of VOCs that significantly contribute to ozone generation were m,p-xylene, ethylene, toluene, propylene, and o-xylene. The key reactive species that significantly contribute to secondary organic aerosols (SOA) were toluene, m,p-xylene, ethylbenzene, o-xylene, and 1,2,3-trimethylbenzene.

The impact of volatile organic compounds on ozone formation in the suburban area of Shanghai

Abstract Volatile organic compounds (VOCs) are important precursors of photochemical smog and secondary organic aerosol (SOA). Quantitatively assessing the impact of VOCs on ozone (O3) formation could provide valuable information for the management of emission reduction and photochemical pollution control. In this study, we first figured out the ozone pollution episodes during 2018 at Dianshan Lake (DSL), which is located in the suburban area of Shanghai and is adjacent to three provinces of the YRD region. Then we analyzed continuous variation of O3 precursors and meteorological parameters. The online measurements show that the average volume mixing ratio of total VOCs (TVOC) was 15.41 ± 11.39 ppbv during the ozone pollution episodes, with the largest contribution from alkanes. To further identify the sources of VOCs, VOC concentration-weighted trajectories (CWT) were analyzed, and the results suggested that Zhejiang province could be the most important source region of VOCs at DSL. Analysis using an observation-base model showed that NOx and alkenes exhibited the most significant negative and positive influences on O3 formation, respectively. As for individual species, toluene and isoprene, whose S-weighted concentrations were 6.67 × 10−2 and 5.94 × 10−2 ppbv, respectively, were the key factors promoting the formation of O3 at DSL. To control the increase of O3, considering the policy feasibility, the abatement ratio of VOCs/NOx should be no less than 0.72. The findings advanced our knowledge of VOCs and their impact on O3 formation and will be helpful in formulating emission control strategies for coping with O3 pollution in YRD region.

Vegetation feedbacks during drought exacerbate ozone air pollution extremes in Europe

Reducing surface ozone to meet the European Union’s target for human health has proven challenging despite stringent controls on ozone precursor emissions over recent decades. The most extreme ozone pollution episodes are linked to heatwaves and droughts, which are increasing in frequency and intensity over Europe, with severe impacts on natural and human systems. Here, we use observations and Earth system model simulations for the period 1960–2018 to show that ecosystem–atmosphere interactions, especially reduced ozone removal by water-stressed vegetation, exacerbate ozone air pollution over Europe. These vegetation feedbacks worsen peak ozone episodes during European mega-droughts, such as the 2003 event, offsetting much of the air quality improvements gained from regional emissions controls. As the frequency of hot and dry summers is expected to increase over the coming decades, this climate penalty could be severe and therefore needs to be considered when designing clean air policy in the European Union. Despite strict controls on precursor emissions, ozone air pollution has not decreased over Europe in recent decades. This is largely attributed to water-stressed vegetation; during heatwaves and drought, plants are less effective at ozone removal via stomata, worsening peak ozone pollution episodes.

A Stratospheric Intrusion-Influenced Ozone Pollution Episode Associated with an Intense Horizontal-Trough Event

Ozone pollution is currently a serious issue in China. As an important source of tropospheric ozone, the stratospheric ozone has received less concern. This study uses a combination of ground-based ozone measurements, the latest ERA5 reanalysis data as well as chemistry-climate model and Lagrangian Particle Dispersion Modeling (LPDM) simulations to investigate the potential impacts of stratospheric intrusion (SI) on surface ozone pollution episodes in eastern China. Station-based observations indicate that severe ozone pollution occurred from 27 April to 28 April 2018 in eastern China, with maximal values over 140 ppbv. ERA5 meteorological and ozone data suggest that a strong horizontal-trough exists at the same time, which leads to an evident SI event and brings ozone-rich air from the stratosphere to the troposphere. Using a stratospheric ozone tracer defined by NCAR’s Community Atmosphere Model with Chemistry (CAM-Chem), we conclude that this SI event contributed about 15 ppbv (15%) to the surface ozone pollution episode during 27–28 April in eastern China. The potential impacts of SI events on surface ozone variations should be therefore considered in ozone forecast and control.

Spatiotemporal characteristics of ozone pollution and policy implications in Northeast China

The ground-level ozone (O3) pollution has become an emerging air quality issue in China. To effectively mitigate ozone pollution in Northeast China (NEC), this study focuses on its characteristics based on the surface ozone, meteorological data, and Ozone Monitoring Instrument (OMI) satellite data. Statistical methods are applied to analyze the effects of meteorology on O3 pollution. The results show that the area and annual averaged maximum 8-h average O3 concentrations rose from 81.3 to 87.4 μg/m3 during 2015–2018 and the nonattainment days kept increasing. The ground-observed O3 concentrations and OMI ozone vertical column densities (VCDs) displayed the pattern of highs in the southwest and lows the northeast of the NEC region with the exceedance areas mainly located over the Liaoning and Jilin provinces in spring and summer. The long-term series of O3, HCHO and NO2 VCDs averaged over NEC all exhibited annual upward trends. Indicated by the OMI HCHO/NO2 ratio, the seasonal and spatial O3-VOCs-NOx sensitivities in NEC provide the control measure guidance for government agencies. Also the ozone control measure needs to consider the biogenic emissions along with the anthropogenic VOCs emissions due to the vast forest areas and large-scale agricultural production in NEC. The ozone pollution episodes in NEC were correlated with weather conditions of high temperature, low relative humidity, long sunshine duration and southwesterly wind in summer and the impact of the East Asia summer monsoon cannot be ignored. Future investigation into VOCs’ measurements and emission inventories are much needed for ozone pollution control in NEC.

Impact of typhoon periphery on high ozone and high aerosol pollution in the Pearl River Delta region

This paper analyzes observation data in the Pearl River Delta (PRD) region from 2012 to 2013, and explores the impact of typhoon periphery on high ozone and high aerosol pollution episodes (double high episodes). Observation analysis show that severe tropical storms to severe typhoons are mainly located in the range of 10°N-30°N, 116°E-135°E when double high episodes occur. Meanwhile, obvious high temperature, low humidity, low wind speed, high actinic flux, high aerosol optical depth (AOD), and high single scattering albedo (SSA) can be observed in double high episodes.The diurnal cycle of the PM2.5 is significant in double high episodes, and the average peak concentration in the afternoon can exceed 90 μg/m3. The diurnal cycle of PM2.5 in non–double high episodes is not significant, and the average value is about 34–39 μg/m3. The ozone peak concentration in double high episodes is 81–103 ppbv, which is about 27–40 ppbv higher than that of non–double high episodes. High correlation can be found between the aerosol and ozone diurnal cycles in double high episodes, and r2 reaches 0.76. In double high episodes, black carbon, nitrate, and sea salt decrease while sulfate, ammonium, secondary organic carbon, and total PM2.5 significantly increase in the afternoon. The growth of PM2.5 in double high episodes is mainly contributed by scattered fine particles from photochemical processes and transmission. The mechanisms that control the double high episodes in the PRD are described below. Ozone and aerosol begin to accumulate under unfavorable meteorological conditions. Via local photochemical processes and external transport, the scattered aerosol increases and leads to an increase in multiple scattering and actinic radiation, which is in turn more favorable for photochemical reaction and further increases the ozone concentration. Meanwhile, high oxidizability promotes the formation of scattered aerosol, creating positive feedback. In addition, the scattered aerosol increases backscattering, which increases the photolysis rate and ozone concentration in the middle and upper boundary layer. Meanwhile, downdraft and turbulence transports high-concentration ozone to the ground.

An important mechanism of regional O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; transport for summer smog over the Yangtze River Delta in eastern China

Abstract. Severe ozone (O3) pollution episodes plague a few regions in eastern China at certain times of the year, e.g., the Yangtze River Delta (YRD). However, the formation mechanisms, including meteorological factors, contributing to these severe pollution events remain elusive. A severe summer smog stretched over the YRD region from 22 to 25 August 2016. This event displayed hourly surface O3 concentrations that exceeded 300 µg m−3 on 25 August in Nanjing, an urban area in the western YRD. The weather pattern during this period was characterized by near-surface prevailing easterly winds and continuous high air temperatures. The formation mechanism responsible for this O3 pollution episode over the YRD region, particularly the extreme values over the western YRD, was investigated using observation data and by running simulations with the Weather Research and Forecasting model with Chemistry (WRF-Chem). The results showed that the extremely high surface O3 concentration in the western YRD area on 25 August was largely due to regional O3 transport in the nocturnal residual layer (RL) and the diurnal change in the atmospheric boundary layer. On 24 August, high O3 levels, with peak values of 220 µg m−3, occurred in the daytime mixing layer over the eastern YRD region. During nighttime from 24 to 25 August, a shallow stable boundary layer formed near the surface which decoupled the RL above it from the surface. Ozone in the decoupled RL remained quite constant, which resulted in an O3-rich “reservoir” forming in this layer. This reservoir persisted due to the absence of O3 consumption from nitrogen oxide (NO) titration or dry deposition during nighttime. The prevailing easterly winds in the lower troposphere governed the regional transport of this O3-rich air mass in the nocturnal RL from the eastern to the western YRD. As the regional O3 transport reached the RL over the western YRD, O3 concentrations in the RL accumulated and rose to 200 µg m−3 over the western Nanjing site during the sunrise hours on 25 August. The development of the daytime convective boundary layer after sunrise resulted in the disappearance of the RL, as the vertical mixing in the convective boundary layer uniformly redistributed O3 from the upper levels via the entrainment of O3-rich RL air down to the O3-poor air at the ground. This net downward transport flux reached up to 35 µg m−3 h−1, and contributed a considerable surface O3 accumulation, resulting in severe daytime O3 pollution during the summer smog event on 25 August in the western YRD region. The mechanism of regional O3 transport through the nocturnal RL revealed in this study has great implications regarding understanding O3 pollution and air quality change.

Understanding long-term variations of meteorological influences on ground ozone concentrations in Beijing During 2006–2016

Recently, ground ozone has become one major airborne pollutant and the frequency of ozone-induced pollution episodes has increased rapidly across China. However, due to the lack of long-term observation data, relevant research on the characteristics and influencing factors of urban ozone concentrations remains limited. Based on ground ozone observation data during 2006–2016, we quantified the causality influence of individual meteorological factors on ozone concentrations in Beijing using a convergent cross mapping (CCM) method. The result indicated that the influence of each meteorological factor on ozone concentrations varied significantly across seasons and years. At the inter-annual scale, all-year meteorological influences on ozone concentrations were much more stable than seasonal meteorological influences. At the seasonal scale, meteorological influences on ozone concentrations were stronger in spring and autumn. Amongst multiple individual factors, temperature was the key meteorological influencing factor for ozone concentrations in all seasons except winter, when wind, humidity and SSD exerted major influences on ozone concentrations. In addition to temperature, air pressure was another meteorological factor that exerted strong influences on ozone concentrations. At both the inter-annual and seasonal scale, the influence of temperature and humidity on ozone concentrations was generally stable whilst that of other factors experienced large variations. Different from PM2.5, meteorological influences on ozone concentrations were relatively weak in summer, when ozone concentrations were the highest in Beijing. Given the generally stable meteorological influences on ozone concentrations and human-induced emissions of VOCs and NOx across seasons, warming induced notable increase in summertime biogenic emissions of VOCs and NOx can be a major driver for the increasing ozone pollution episodes. This research provides useful references for understanding long-term meteorological influences on ozone concentrations in mega cities in China.

Ozone formation and key VOCs in typical Chinese city clusters

China, especially Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD), Pearl River Delta (PRD), and Sichuan Basin (SCB), suffers from severe ozone pollution problems during summer and autumn. Ground-level ozone is formed via a series of complex photochemical reactions between nitrogen oxides (NO x ) and volatile organic compounds (VOCs), which are one of the most concerning pollutants in the four megacities and have adverse impacts on human health. In recent years, O3 concentrations that exceed the national ambient air quality standard have been frequently observed during summer and autumn. However, the mechanism of O3 formation and the key factors that regulate this mechanism have not been studied in detail. To evaluate ozone pollution episodes in Chinese megacities, field observation data of O3 and its precursors at 20 sites in the four major urban regions during summer and autumn from 2014 to 2016 were collected in this study. We found that all the four regions suffered from serious O3 pollution. The daily maximum 8-hour average O3 concentrations ranged from 59–146 (10−9 V/V). Moreover, the hourly maximum O3 concentrations were in the range of 73–187 (10−9 V/V). High values of both these parameters were measured at the same site, Dingling, which is a rural area of Beijing. Furthermore, O3 concentrations in urban areas were lower than those in suburban regions. Ozone non-attainment days occurred more frequently in BTH and YRD than in the other regions. Although the concentrations of NO x and VOCs, which are ozone precursors, varied largely across different sites, they were generally in ranges of ~4–22 (10−9 V/V) and 11–53 (10−9 V/V), respectively. Additionally, isoprene reactivity significantly contributed to total the VOC reactivity ( k VOC) in rural sites. However, in urban sites, the reactivities of alkenes and aromatics were significant contributors. To evaluate the effectiveness of various ozone precursor control strategies in reducing ozone pollution, we combined the observation-based model (OBM) with the relative incremental reactivity (RIR) method. The sensitivity of O3 production was studied by varying the emission of ozone precursors at each site and the key indicators that affect the local ozone production rate were identified. The ozone precursors were divided into four groups: anthropogenic hydrocarbons (AHC), which consist of alkanes, alkenes, and aromatics, natural hydrocarbons (NHC, only isoprene), NO x , and CO. It was found that most of the sites in these four regions were in a VOC-limited regime or transition regime (VOC and NO x sensitive) and the key VOC precursors were alkenes and aromatics. Additionally, an empirical kinetic modeling approach (EKMA) was used to determine the cooperative control scheme for NO x and VOCs. Most of the urban sites were under VOC-limited conditions while the suburban site was in a NO x -limited regime. These results are consistent with the results derived with the RIR method. To further explore the role of anthropogenic emissions in ozone pollution, we used the positive matrix factorization (PMF) model to identify the major sources contributing to VOCs. This model identified five to seven VOCs sources in different urban sites. The major sources for these sites were vehicular exhaust and gasoline evaporation, accounting for 30%–50% of the observed VOCs. According to the source profile, a series of sensitivity tests were performed by reducing each source by 20% to determine the RIR of the individual source. Vehicular exhaust and solvent utilization were the major contributors to O3 formation in Dongsi, Pudong, Modiesha, and Chaozhan, which are located in BTH, YRD, PRD, and SCB, respectively. In summary, by regulating VOCs emissions, especially vehicular emissions and emissions from solvent use, the O3 concentration in China can be efficiently regulated.

Exploration of the formation mechanism and source attribution of ambient ozone in Chongqing with an observation-based model

An intensive field campaign was conducted in Chongqing during the summer of 2015 to explore the formation mechanisms of ozone pollution. The sources of ozone, the local production rates, and the controlling factors, as well as key species of volatile organic compounds (VOCs), were quantified by integrating a local ozone budget analysis, calculations of the relative incremental reactivity, and an empirical kinetic model approach. It was found that the potential for rapid local ozone formation exists in Chongqing. During ozone pollution episodes, the ozone production rates were found to be high at the upwind station Nan Quan, the urban station Chao Zhan, and the downwind station Jin-Yun Shan. The average local ozone production rate was 30× 10−9 V/V h−1 and the daily integration of the produced ozone was greater than 180×10−9 V/V. High ozone concentrations were associated with urban and downwind air masses. At most sites, the local ozone production was VOC-limited and the key species were aromatics and alkene, which originated mainly from vehicles and solvent usage. In addition, the air masses at the northwestern rural sites were NO x -limited and the local ozone production rates were significantly higher during the pollution episodes due to the increased NO x concentrations. In summary, the ozone abatement strategies of Chongqing should be focused on the mitigation of VOCs. Nevertheless, a reduction in NO x is also beneficial for reducing the regional ozone peak values in Chongqing and the surrounding areas.

Emulation and Sensitivity Analysis of the Community Multiscale Air Quality Model for a UK Ozone Pollution Episode.

Gaussian process emulation techniques have been used with the Community Multiscale Air Quality model, simulating the effects of input uncertainties on ozone and NO2 output, to allow robust global sensitivity analysis (SA). A screening process ranked the effect of perturbations in 223 inputs, isolating the 30 most influential from emissions, boundary conditions (BCs), and reaction rates. Community Multiscale Air Quality (CMAQ) simulations of a July 2006 ozone pollution episode in the UK were made with input values for these variables plus ozone dry deposition velocity chosen according to a 576 point Latin hypercube design. Emulators trained on the output of these runs were used in variance-based SA of the model output to input uncertainties. Performing these analyses for every hour of a 21 day period spanning the episode and several days on either side allowed the results to be presented as a time series of sensitivity coefficients, showing how the influence of different input uncertainties changed during the episode. This is one of the most complex models to which these methods have been applied, and here, they reveal detailed spatiotemporal patterns of model sensitivities, with NO and isoprene emissions, NO2 photolysis, ozone BCs, and deposition velocity being among the most influential input uncertainties.

Impact of global climate change on ozone, particulate matter, and secondary organic aerosol concentrations in California: A model perturbation analysis

Air quality simulations are performed to determine the impact of changes in future climate and emissions on regional air quality in the South Coast Air Basin (SoCAB) of California. The perturbation parameters considered in this study include (1) temperature, (2) absolute humidity, (3) biogenic VOC emissions due to temperature changes, and (4) boundary conditions. All parameters are first perturbed individually. In addition, the impact of simultaneously perturbing more than one parameter is analyzed. Air quality is simulated with meteorology representative of a summertime ozone pollution episode using both a baseline 2005 emissions inventory and a future emissions projection for the year 2023. Different locations within the modeling domain exhibit varying degrees of sensitivity to the perturbations considered. Afternoon domain wide average ozone concentrations are projected to increase by 13–18% as a result of changes in future climate and emissions. Afternoon increases at individual locations range from 10 to 36%. The change in afternoon particulate matter (PM) levels is a strong function of location in the basin, ranging from −7.1% to +4.7% when using 2005 emissions and −8.6% to +1.7% when using 2023 emissions. Afternoon secondary organic aerosol (SOA) concentrations for the entire domain are projected to decrease by over 15%, and the change in SOA levels is not a strong function of the emissions inventory utilized. Temperature increases play the dominant role in determining the overall impact on ozone, PM, and SOA concentrations in both the individual and combined perturbation scenarios.

Assessing the impact of local meteorological variables on surface ozone in Hong Kong during 2000–2015 using quantile and multiple line regression models

The quantile regression (QR) method has been increasingly introduced to atmospheric environmental studies to explore the non-linear relationship between local meteorological conditions and ozone mixing ratios. In this study, we applied QR for the first time, together with multiple linear regression (MLR), to analyze the dominant meteorological parameters influencing the mean, 10th percentile, 90th percentile and 99th percentile of maximum daily 8-h average (MDA8) ozone concentrations in 2000–2015 in Hong Kong. The dominance analysis (DA) was used to assess the relative importance of meteorological variables in the regression models. Results showed that the MLR models worked better at suburban and rural sites than at urban sites, and worked better in winter than in summer. QR models performed better in summer for 99th and 90th percentiles and performed better in autumn and winter for 10th percentile. And QR models also performed better in suburban and rural areas for 10th percentile. The top 3 dominant variables associated with MDA8 ozone concentrations, changing with seasons and regions, were frequently associated with the six meteorological parameters: boundary layer height, humidity, wind direction, surface solar radiation, total cloud cover and sea level pressure. Temperature rarely became a significant variable in any season, which could partly explain the peak of monthly average ozone concentrations in October in Hong Kong. And we found the effect of solar radiation would be enhanced during extremely ozone pollution episodes (i.e., the 99th percentile). Finally, meteorological effects on MDA8 ozone had no significant changes before and after the 2010 Asian Games.