Variations Of O3 Concentrations Research Articles

Comparison of Surface Ozone Variability in Mountainous Forest Areas and Lowland Urban Areas in Southeast China

The ozone (O3) variations in southeast China are largely different between mountainous forest areas located inland, and lowland urban areas located near the coast. Here, we selected these two kinds of areas to compare their similarities and differences in surface O3 variability from diurnal to seasonal scales. Our results show that in comparison with the lowland urban areas (coastal areas), the mountainous forest areas (inland areas) are characterized with less human activates, lower precursor emissions, wetter and colder meteorological conditions, and denser vegetation covers. This can lead to lower chemical O3 production and higher O3 deposition rates in the inland areas. The annual mean of 8-h O3 maximum concentrations (MDA8 O3) in the inland areas are ~15 μg·m−3 (i.e. ~15%) lower than that in the coastal areas. The day-to-day variation in surface O3 in the two types of the areas is rather similar, with a correlation coefficient of 0.75 between them, suggesting similar influences on large scales, such as weather patterns, regional O3 transport, and background O3. Over 2016–2020, O3 concentrations in all the areas shows a trend of “rising and then falling”, with a peak in 2017 and 2018. Daily MDA8 O3 correlates with solar radiation most in the coastal areas, while in the inland areas, it is correlated with relative humidity most. Diurnally, during the morning, O3 concentrations in the inland areas increase faster than in the coastal areas in most seasons, mainly due to a faster increase in temperature and decrease in humidity. While in the evening, O3 concentrations decrease faster in the inland areas than in the coastal areas, mostly attributable to a higher titration effect in the inland areas. Seasonally, both areas share a double-peak variation in O3 concentrations, with two peaks in spring and autumn and two valleys in summer and winter. We found that the valley in summer is related to the summer Asian monsoon that induces large-scale convections bringing local O3 upward but blocking inflow of O3 downward, while the one in winter is due to low O3 production. The coastal areas experienced more exceedance days (~30 days per year) than inland areas (~5-10 days per year), with O3 sources largely from the northeast. Overall, the similarities and differences in O3 concentrations between inland and coastal areas in southeastern China are rather unique, reflecting the collective impact of geographic-related meteorology, O3 precursor emissions, and vegetation on surface O3 concentrations.

Recent-year variations in O3 pollution with high-temperature suppression over central China

By analyzing environmental and meteorological monitoring data over recent years of 2015–2022, the Twain-Hu Basin (THB) in central China was identified as a regional O3 pollution center over China with the highest increasing trend at 1.10 %⸱yr−1 in interannual variations of O3 concentrations with deteriorating O3 pollution over recent years. We explored the spatiotemporal variations in O3 pollution in the THB with ozone suppression (OS) under high air temperature over metropolitan, small urban, and mountainous areas. The bipolarized interannual trends in interannual O3 variations in urban and mountainous areas over central China were characterized with the increasing and decreasing 90th percentiles of the daily maximum 8-h (MDA8-90) O3 concentrations respectively in polluted urban areas and clean mountainous areas over recent eight years. The changes of the near-surface O3 concentrations with air temperature exhibited the inflection points of OS from increasing to decreasing O3 at air temperature of 30.5 °C in mountainous areas, 32.5 °C in small urban areas, and 34.5 °C in metropolitan areas, and the intensity of OS was estimated in the ranking with mountainous areas (−2.30 μg⸱m−3⸱°C−1) > small urban areas (−1.96 μg⸱m−3⸱°C−1) > metropolitan areas (−1.54 μg⸱m−3⸱°C−1), indicating that the OS was more significant over the lower-O3 mountainous areas. This study has implications for understanding O3 pollution variations with the meteorological drivers.

Trends of the Global Burden of Disease Linked to Ground-Level Ozone Pollution: A 30-Year Analysis for the Greater Athens Area, Greece

The Greater Athens Area (GAA), situated in the southern part of the European continent (in Greece), has a Mediterranean climate characterized by hot, dry summers and mild, wet winters. As a result of increased sunshine and high temperatures, exceedances in ozone concentrations are often recorded during the hot period. In the present study, the monthly as well as daily variations of O3 concentrations at thirteen stations in the GAA were investigated for the period 1987–2019. Moreover, the impact of O3 on the people’s health in Greece was examined by using data from the Global Burden of Disease (GBD) study with the socio-economic conditions of the country. Ozone concentrations were found to be particularly high during the summer months, especially in suburban stations. Values ranged from 65 μg/m3 to 90 μg/m3 during the night, in contrast to urban areas and remain high for several hours. Comparing estimates from GBD, it was found that exposure to ozone can impair respiratory function, leading to death or susceptibility to respiratory diseases that reduce quality of life, especially for people over 55 years of age. Finally, since 2009, when the economic crisis began in Greece, an upward trend was observed for deaths and disability adjusted life years.

Simple model of vertical dispersion of O3 in Bangkok, Thailand using regression method

Bangkok, the capital city of Thailand, has experienced a degradation in air quality. In particular, ozone (O3) concentrations frequently exceed Thailand’s National Ambient Air Quality standards. Various policies have been developed to manage air quality at near-surface levels; however, the assessment of air quality above these levels has been neglected. Analysis of O3 concentrations and its precursors measured at various altitudes revealed that the vertical structures of the pollutants in Bangkok were stratified. While NOx concentrations decreased with height, O3 concentrations increased. These results emphasize the importance of air quality management above ground level, particularly in megacities with high-rise buildings, such as Bangkok. Assuming that the O3 formation regime over Bangkok is VOC-limited, a simple model was developed based on a linear regression method to estimate the changes in O3 concentrations with height. We found that the simple model was able to capture the variation in O3 concentrations at 30, 75, and 110 m above ground level, with an R2 of 0.48–0.65. Although the simple model had some difficulty estimating the magnitude of O3 concentrations, the estimated O3 values from the model were reasonable for capturing vertical O3 trends. Using this approach, policymakers can visualize the vertical distribution of pollutants, which will be useful in designing air quality management plans.

Study on O3 Variations in Nanjing and the Surrounding Source Analysis

To understand the transport patterns and major sources of ozone (O3) in Nanjing, this study carried out the 48-hour backward trajectories of air masses in Nanjing from March 2021 to March 2022, based on the HYSPLIT backward trajectory model driven by GDAS global reanalysis data. The primary transmission routes and putative source locations of O3 pollution in Nanjing were determined through the integration of trajectory clustering analysis, potential source contribution function (PSCF), and concentration-weighted trajectory (CWT) analysis with meteorological data and O3 concentration data. The results showed that the high O3 concentrations and exceedance rates in Nanjing were in late spring and early summer, with the highest in June. The diurnal variation of O3 concentrations in all seasons exhibited a single peak with a maximum from 13:00 to 16:00. The southeasterly flow passing through Zhenjiang, Changzhou, Wuxi, Suzhou, and Shanghai dominated the O3 pollution in Nanjing. The PSCF and CWT presented a high consistency of O3 potential sources in Nanjing. Zhenjiang, Ma’anshan, Changzhou, Wuxi, Suzhou, and Huzhou were identified as the main potential source regions of O3 pollution in Nanjing. This study provides accurate theoretical references for regional joint prevention and control of O3 pollution in Nanjing.

Spatio-temporal variation of O3 concentration and exposure risk assessment in key regions of China, 2015–2021

In recent years, the increasing Ozone (O3) concentration has become a significant concern for human life and health. In this study, O3 concentration data at 10 km resolution and population density data at 1 km resolution for China were utilized. Methods such as the Global Moran's I index, Getis-Ord Gi* index, and population exposure risk index, to analyze the spatial-temporal variation, meteorological influences, aggregation characteristics, exposure risk levels and health impact of O3 in China and six key regions from 2015 to 2021. The results revealed an increasing trend with a bimodal fluctuation pattern, peak in May and August. Only Pearl River Delta (PRD) showed the highest in autumn, five other key regions were highest O3 concentration in the summer. And the spatial autocorrelation in China is obvious among regions. Among the five meteorological factors, temperature and sunshine duration predominantly influenced O3 concentration in China. Relative humidity was the main factor affecting O3 concentration in Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD) and Sichuan Basin (SCB), while precipitation had the greatest impact on FenWei Plain (FWP) and Hexi Corridor (HXC) and exhibited a positive correlation. Wind speed in PRD showed a strong negative correlation with O3 concentration. The Ri exhibited significant differences between the eastern and western sides of the Hu Huanyong line, demonstrating a distribution pattern of "high in the east and low in the west". Through this research, we aim to provide valuable insights for public health policies and the prevention and control of regional air pollution.

Spatial and temporal distribution of PM2.5 and O3 in north China from 2011 to 2020: Patterns and influence mechanisms

Based on PM2.5 and O3 concentration data in North China from 2011 to 2020, the spatial and temporal distribution characteristics of PM2.5 and O3 concentrations were explored using Sen's slope estimation, hot spot analysis, and a spatial center of gravity shift model, and the intensity of the influence of meteorological and socio-economic factors on PM2.5 and O3 concentrations was analyzed using a geographical detector. The results indicate that (1) PM2.5 concentrations in North China exhibit a seasonal pattern of "high in spring and winter and low in summer and autumn" with an average monthly decrease of 0.1625 μg/m3 and an average annual decrease of 1.95 μg/m3. O3 concentrations exhibit a trend of "high in summer and autumn and low in spring and winter" with an average monthly decrease of 0.0108 μg/m3 and an average annual decrease of 0.1296 μg/m3. (2) The centers of gravity of PM2.5 and O3 concentrations migrated in similar directions during the study period with a clear southeastward migration feature. (3) PM2.5 and O3 concentrations possess obvious spatial aggregation characteristics, and the degree of pollution aggregation diminishes with PM2.5 hot spot areas concentrated in southern Hebei Province and cold spot areas concentrated in Zhangjiakou and Hohhot in North China. O3 concentrations are the opposite of PM2.5 concentration spatial aggregation. (4) The single-factor results indicated that ground pressure, average annual temperature, and population density all exerted prominent effects on PM2.5, whereas variations in O3 concentrations were primarily influenced by meteorological factors. (5) Interaction detection demonstrated that the interactions among the influencing factors exhibited a greater explanatory power than did the single factor effect on both PM2.5 and O3 concentration changes.

Prediction of ozone pollution impacted by vegetation planning in the Pearl River Delta, China

Controlling severe ozone (O3) pollution has become an urgent issue for addressing air pollution control in the Pearl River Delta (PRD) region of China. Biogenic volatile organic compounds (BVOCs) are the main precursors of O3 formation. Changes in vegetation type because of anthropogenic disturbances alter BVOCs emissions in the PRD. In this study, WRF-Chem4.1.2 coupled with MEGAN2.1 was applied to predict the impact of changes in BVOCs because of the replacement of vegetation plans on O3 pollution in the PRD. This is based on changes in the distribution of vegetation types in a range of sensitive areas. The results have indicated that the scenario with the greatest disturbance to O3 concentrations is the replacement of the forest type in the volatile organic compounds (VOCs) sensitive area with the dryland cropland and pastureland use type. Here, the reduction in isoprene concentrations in the PRD River could reach 63% of the area. The reduction in O3 concentrations reached 48% of the area, with a maximum reduction of 8.8%. The effect of vegetation planning on O3 has a clear “spillover” phenomenon. Variations in O3 concentrations greater than 1% were predominantly distributed outside the range of land use type changes, accounting for 80%–91% of the change. There was a linear fit for meteorological conditions and the amount of variation in precursor concentrations with O3 concentrations in the “spillover” region. BVOCs were found to have a greater effect on the variation in O3 concentrations.

Characteristics, sources and health risk assessment of atmospheric carbonyls during multiple ozone pollution episodes in urban Beijing: Insights into control strategies

Carbonyls have attracted continuous attention due to their critical roles in atmospheric chemistry and their potential hazards to the ecological environment and human health. In this study, atmospheric carbonyls were measured during several ground-level-ozone (O3) pollution episodes at three urban sites (CRAES, IEP and BJUT) in Beijing in 2019 and 2020. Comparative analysis revealed that the carbonyl concentrations were 20.25 ± 6.91 ppb and 13.43 ± 5.13 ppb in 2019 and 2020 in Beijing, respectively, with a significant spatial trend from north to south, and carbonyl levels in urban Beijing were in an upper-intermediate range in China, and higher than those in other countries reported in the literature. A particularly noteworthy phenomenon is the consistency of carbonyl concentrations with variations in O3 concentrations. On O3 polluted days, the carbonyl concentrations were 1.3–1.5 times higher than those on non-O3 polluted days. Secondary formation contributed more to formaldehyde (FA) and acetaldehyde (AA) on O3 polluted days, while the anthropogenic emissions were more significant for acetone (AC) on non-O3 polluted days. Vehicle exhaust and solvent utilization were the main primary contributors to carbonyls. Due to reduced anthropogenic emissions caused by the COVID-19 lockdown and the “Program for Controlling Volatile Organic Compounds in 2020” in China, the contributions of primary emissions to carbonyls decreased in 2020 in Beijing. Human cancer risks to exposed populations from FA and AA increased with elevated O3 levels, and the risks still remained on non-O3 polluted days. The residents around the BJUT site might experience relatively higher human cancer risks than those around the other two sites. The findings in this study confirmed that atmospheric carbonyl pollution and its potential human health hazards cannot be ignored in urban Beijing; therefore, more strict control strategies for atmospheric carbonyls are urgently needed to better protect human health in Beijing in the future.

16 Years (2006–2021) of Surface Ozone Measurements in Córdoba (Southern Spain): Trends and the Impact of the COVID-19 Lockdown

Surface ozone concentrations (O3) during the period 2006-2021 are analysed at Córdoba city (southern Iberian Peninsula) in suburban and urban sampling sites. The aims are to present the levels and temporal variations, to explore trends and to quantity the variation in O3 concentrations in the context of the COVID-19 lockdown. The O3 means are higher in the suburban station (62 µg m-3 and 51.3 µg m-3), being the information level threshold only exceeded twice during this period. The daily evolution shows a maximum at about 17:00 UTC, whereas the minimum is reached at about 9:00 UTC, with higher levels in the suburban station. The seasonal evolution of this daily cycle also presents monthly differences in shape and intensity between stations. The trends are analysed by means of daily averages and daily 5th and 95th percentiles, and they show a similar increase in all of these parameters, with special emphasis on the daily P95 concentrations, with 0.27 µg m-3 year-1 and 0.24 µg m-3 year-1. Finally, the impact of the COVID-19 lockdown shows a decline in O3 concentrations over 10%.

Analysis of the Spatial and Temporal Patterns of Ground-Level Ozone Concentrations in the Guangdong–Hong Kong–Macao Greater Bay Area and the Contribution of Influencing Factors

Ozone (O3) pollution has negative impacts on human health and property. The Guangdong–Hong Kong–Macao Greater Bay Area (GBA) is facing severe O3 pollution problems due to rapid economic development. In this paper, we used sensitivity experiments and GeoDetector to analyze the effects of meteorological factors, anthropogenic emissions, and landscape patterns on O3 concentrations as well as the contributions of NOx and NMVOC (non-methane volatile organic compounds) to the variation of O3 concentrations and the causes of sectoral emissions in the GBA in 2017. The results revealed that, in GBA, the contribution of meteorology to the variation of O3 concentration was dominant both in terms of region and extent, and the contribution of emissions was relatively weak. The contribution of meteorology and emissions to O3 production was mainly contributory. Meteorology contributed significantly to O3, and its non-linear interaction with anthropogenic emissions and surface landscape affected O3 concentration changes. The degree of contribution of NOx and NMVOC varied widely among seasons, and the variation of their relative contribution areas was related to residential sector emissions and agricultural sector emissions. This article enriches the exploration of the O3 formation mechanism in the GBA and provides theoretical support for the implementation of differentiated regional and seasonal mitigation strategies for O3 concentration.

Effects of Weather and Anthropogenic Precursors on Ground-Level Ozone Concentrations in Malaysian Cities

Ground-level ozone (O3) is a significant source of air pollution, mainly in most urban areas across the globe. Ground-level O3 is not emitted directly into the atmosphere. It results from photo-chemical reactions between precursors and is influenced by weather factors such as temperature. This study investigated the spatial and temporal analysis of ground-level ozone and analyzed the significant anthropogenic precursors and the weather parameters associated with ground-level ozone during daytime and nighttime at three cities in peninsular Malaysia, namely, Kuala Terengganu, Perai, and Seremban from 2016 to 2020. Secondary data were acquired from the Department of Environment (DOE), Malaysia, including hourly data of O3 with trace gases and weather parameters. The secondary data were analyzed using temporal analysis such as descriptive statistics, box plot, and diurnal plot as well as spatial analysis such as contour plot and wind rose diagram. Spearman correlation was used to identify the association of O3 with its precursors and weather parameters. The results show that a higher concentration of O3 during the weekend due to “ozone weekend effects” was pronounced, however, a slightly significant effect was observed in Perai. The two monsoonal seasons in Malaysia had a minimal effect on the study areas except for Kuala Terengganu due to the geographical location. The diurnal pattern of O3 concentration indicates bimodal peaks of O3 precursors during the peak traffic hours in the morning and evening with the highest intensity of O3 precursors detected in Perai. Spearman correlation analysis determined that the variations in O3 concentrations during day and nighttime generally coincide with the influence of nitrogen oxides (NO) and temperature. Lower NO concentration will increase the amount of O3 concentration and an increasing amount of O3 concentration is influenced by the higher temperature of its surroundings. Two predictive models, i.e., linear (multiple linear regression) and nonlinear models (artificial neural network) were developed and evaluated to predict the next day and nighttime O3 levels. ANN resulted in better prediction for all areas with better prediction identified for daytime O3 levels.

Long time series ozone prediction in China: A novel dynamic spatiotemporal deep learning approach

Ozone pollution is a global environmental problem becoming increasingly prominent in China. It is of great significance to achieve long-term and high-precision ground-level ozone prediction on large scales to improve the efficiency of environmental governance. In this paper, we developed a dynamic graph convolutional and sequence to sequence embedded with the attention mechanism model (DG-ASeqseq) for predicting daily maximum 8-h average ozone (MDA8 O3) concentrations over China the next seven days. In the proposed approach, changeable spatial correlations are modelled by graph convolutional operations on dynamic graphs constructed based on multiple information of historical change, and temporal correlations in long time series are modelled through the sequence to sequence networks embedded with the attention mechanism. Results show the reliability and effectiveness of the proposed model, and it is superior to other benchmark models in simulating long-term spatiotemporal variations of O3 concentrations in large scale areas. Moreover, the proposed model has good prediction capability in severe O3 pollution events. Advancement in this methodology could provide guidance for the government's coordinated control of regional pollution to help improve air quality and jointly safeguard global climate security.

Tropospheric Ozone Perturbations Induced by Urban Land Expansion in China from 1980 to 2017.

Urbanization perturbs air pollutants from a dynamic and thermodynamic perspective, which has inspired extensive investigations in China due to rapid urban land expansion in the past four decades. However, knowledge gaps remain in the long-term and nationwide responses to air pollutants to urbanization. The evolution of tropospheric ozone associated with urban land expansion across China was assessed from 1980 to 2017 using a coupled WRF-Chem model based on a recently updated land use change (LUC) data set. The results revealed that urban-land expansion drove growing ozone trends for this period and contributed about 3-9% to its summer maximum concentrations during the 2010s in major urban agglomerations across China. The association between a long-term change in summer O3 concentrations and LUC after excluding the effect of precursor emissions and meteorological conditions and causes of interannual (short-term) variations in O3 concentrations induced by urban-land expansion were also explored by examining the relationships between ozone fluctuations and meteorological variables.

Model Analyses of Changes in Spring Surface Ozone Concentrations over Shandong Province in the Period of 2014‒2017

The concentrations of surface ozone (O3) in eastern China have increased significantly in recent years, resulting in the earlier appearance of more serious O3 pollution. Measurements at 14 stations in Shandong Province showed that the monthly mean O3 concentrations in the late spring (May) increased by 22.2 µg m−3 from 2014 to 2017. To investigate the reasons of the increase of O3 in springtime from 2014 to 2017, the changes of O3 concentrations due to meteorological conditions and emissions in May were studied based on ambient measurements and simulations with the RAMS-CMAQ modeling system. By analyzing the observed data, it was found that the variations in wind field were conducive to the accumulation of O3, while the effects of other meteorological parameters on O3 concentrations were different at the same site between years. Further to perform a series of simulations with only the meteorological conditions changed in May from 2014 to 2017, the results showed that the effects of variations in meteorological conditions had become more and more important in the changes of O3 concentrations in May between years, especially the factors that affected the photochemical generation of O3. For example, the percentage of the sites where the changes of O3 concentrations were dominated by the variations of the meteorological conditions increased from 28.6% to 78.6% over the region in May between years. Besides, the changes in NOx emissions had a close relationship with the variations in O3 concentrations when the changes of O3 were dominated by the emission variations.

Variation Characteristics Mathematical Calculation of O3 and Its Relationship with Meteorological Factors by Big Data Technology

Based on the data of environmental monitoring stations and meteorological stations in Qinhuangdao from May 2017 to May 2020, the variation characteristics of O3 and precursors (NO2 and CO) as well as their relationship with meteorological elements were analyzed. The results showed that the daily average concentration of O3-8 h in Qinhuangdao increased year by year. The monthly average concentration of O3-8 h was high in summer and low in winter, and the peak appeared in June. The diurnal variation of O3 concentration was unimodal structure, and the concentration increased in the afternoon, but it decreased at night. The concentration of NO2 and CO was inversely correlated with O3, and the peak value of NO2 in March could be related to frequent cold air activity and increased burning of loose coal. The meteorological elements favorable for the occurrence of ozone pollution weather in Chengde were total solar radiation irradiance greater than 1000W/m2, the daily maximum temperature greater than 33 °C, and the daily minimum relative humidity less than 40% and 65%∽80%, southerly wind or southwest wind.

Analysis of Ozone Pollution Characteristics and Influencing Factors in Northeast Economic Cooperation Region, China

The increase in tropospheric ozone (O3) concentration has become one of the factors restricting urban development. This paper selected the important economic cooperation areas in Northeast China as the research object and collected the hourly monitoring data of pollutants and meteorological data in 11 cities from 1 January 2015 to 31 December 2019. The temporal and spatial variation trend of O3 concentration and the effects of meteorological factors and other pollutants, including CO (carbon monoxide), SO2 (sulfur dioxide), NO2 (nitrogen dioxide), and PM2.5 and PM10 (PM particles with aerodynamic diameters less than 2.5 μm and 10 μm) on ozone concentration were analyzed. At the same time, the variation period of O3 concentration was further analyzed by Morlet wavelet analysis. The results showed that the O3 pollution in the study area had a significant spatial correlation. The spatial distribution showed that the O3 concentration was relatively high in the south and low in the northeast. Seasonally, the O3 concentration was the highest in spring, followed by summer, and the lowest in winter. The diurnal variation of O3 concentration presented a “single peak” pattern. O3 concentration had a significant positive correlation with temperature, sunshine duration, and wind speed and a significant anticorrelation with CO, NO2, SO2, and PM2.5 concentration. Under the time scale of a = 9, 23, O3 had significant periodic fluctuation, which was similar to those of wind speed and temperature.

Spatiotemporal Changes of Near-Surface Ozone Concentration From 2015 to 2018 in Beijing

In this study, we investigated the spatiotemporal changes of near-surface O3 concentration based on 33 automatic air quality monitoring stations in Beijing in 2015 and 2018. Here we show that the diurnal variations for O3 concentration at 33 monitoring stations exhibited a single-peak mode with a minimum concentration from 06:00 to 07:00 and a maximum value from 14:00 to 15:00. We find that the O3 concentration was significantly positively correlated with the air temperature, solar total radiation, and wind speed, while it was negatively correlated with the relative humidity. Among those factors, the air temperature played the most important role in influencing O3 concentration (relative contribution is greater than 88% in the boosted regression trees model). We also present that the annual variation of O3 concentration at all stations tended to be a “bell-shaped” curve distribution with a peak in summer and the lowest value in winter. The annual averaged O3 concentration at 33 stations in Beijing was 57.5 ± 9.8 μg⋅m−3 in 2015 and 60.3 ± 9.0 μg⋅m−3 in 2018. In addition, we detect that the annual averaged value of the O3 concentration was lower in the central and southern Beijing, and higher in the northern Beijing both in 2015 and 2018. The spatial difference of the O3 concentration could be explained by the traffic pollution, vegetation coverage, atmospheric regional transmission, and atmospheric particulate matter concentration.

Analysis of wintertime O3 variability using a random forest model and high-frequency observations in Zhangjiakou—an area with background pollution level of the North China Plain

The short-term health effects of ozone (O3) have highlighted the need for high-temporal-resolution O3 observations to accurately assess human exposure to O3. Here, we performed 20-s resolution observations of O3 precursors and meteorological factors to train a random forest model capable of accurately predicting O3 concentrations. Our model performed well with an average validated R2 of 0.997. Unlike in typical linear model frameworks, variable dependencies are not clearly modelled by random forest model. Thus, we conducted additional studies to provide insight into the photochemical and atmospheric dynamic processes driving variations in O3 concentrations. At nitrogen oxides (NOx) concentrations of 10–20 ppb, all the other O3 precursors were in states that increased the production of O3. Over a short timescale, nitrogen dioxide (NO2) can almost track each high-frequency variation in O3. Meteorological factors play a more important role than O3 precursors do in predicting O3 concentrations at a high temporal resolution; however, individual meteorological factors are not sufficient to track every high-frequency change in O3. Nevertheless, the sharp variations in O3 related to flow dynamics are often accompanied by steep temperature changes. Our results suggest that high-temporal-resolution observations, both ground-based and vertical profiles, are necessary for the accurate assessment of human exposure to O3 and the success and accountability of the emission control strategies for improving air quality.

Characteristic of Surface Ozone and Meteorological Parameters Analysis in Anyang City

This study uses the national ambient air quality station data of Anyang City from 2014 to 2017 to analyze the characteristics and variation rules of ozone (O3) in different functional zones (urban, suburban, and industrial), and also studies meteorological influencing factors and potential source distributions of O3 pollution. The results showed that the O3 concentration in Anyang increased significantly between 2014 and 2017, whereby pollution started to advance from 2015 and the earliest occurrence of an O3 pollution episode was in April 2017. The 90th percentile and average concentrations of O3 in the industrial zone increased at faster rates (average annual growth of 16.0 μg·m-3 and 13.0 μg·m-3, respectively) than of those in the urban and suburban zones. The O3 concentrations at the suburban site showed the fastest increase of all zones at the 5th percentile (average annual growth of 13.2 μg·m-3). The monthly variation in O3 concentrations in Anyang showed an "M" pattern that varied spatially depending on the zone. Temperature played a leading role in O3 concentrations; air temperatures >23℃, relative humidity <58%, and a wind speed of 5 m·s-1 in a south-southwesterly direction were closely related to the occurrence of high O3 concentrations. Potential sources of O3 in different seasons were significantly different, and mainly distributed in southern Hebei, northern Hubei, and northern Shenyang in summer. The first heavy O3 pollution day in the studied period was in May 2017, at which time the highest O3 concentration was found in the industrial zone (up to 405 μg·m-3). This heavy O3 pollution episode was related to the continuous high temperature that was caused by the transfer of a dry, hot air mass in western China.