Spatiotemporal Patterns and Regional Transport of Ground-Level Ozone in Major Urban Agglomerations in China

Abstract

Ground-level ozone (O3) pollution has become a serious environmental issue in major urban agglomerations in China. To investigate the spatiotemporal patterns and regional transports of O3 in Beijing–Tianjin–Hebei (BTH-UA), the Yangtze River Delta (YRD-UA), the Triangle of Central China (TC-UA), Chengdu–Chongqing (CY-UA), and the Pearl River Delta urban agglomeration (PRD-UA), multiple transdisciplinary methods were employed to analyze the O3-concentration data that were collected from national air quality monitoring networks operated by the China National Environmental Monitoring Center (CNEMC). It was found that although ozone concentrations have decreased in recent years, ozone pollution is still a serious issue in China. O3 exhibited different spatiotemporal patterns in the five urban agglomerations. In terms of monthly variations, O3 had a unimodal structure in BTH-UA but a bimodal structure in the other urban agglomerations. The maximum O3 concentration was in autumn in PRD-UA, but in summer in the other urban agglomerations. In spatial distribution, the main distribution of O3 concentration was aligned in northeast–southwest direction for BTH-UA and CY-UA, but in northwest–southeast direction for YRD-UA, TC-UA, and PRD-UA. O3 concentrations exhibited positive spatial autocorrelations in BTH-UA, YRD-UA, and TC-UA, but negative spatial autocorrelations in CY-UA and PRD-UA. Variations in O3 concentration were more affected by weather fluctuations in coastal cities while the variations were more affected by seasonal changes in inland cities. O3 transport in the center cities of the five urban agglomerations was examined by backward trajectory and potential source analyses. Local areas mainly contributed to the O3 concentrations in the five cities, but regional transport also played a significant role. Our findings suggest joint efforts across cities and regions will be necessary to reduce O3 pollution in major urban agglomerations in China.

Surface Ozone in the Central Plains Urban Agglomeration, China: Spatial-Temporal Variations and Health Impacts

“…In summer, the relatively high temperature and strong radiation enhance the photochemical reactions, which leads to increased O 3 production. In winter, most regions in China have the lowest O 3 levels [35,36], while a high O 3 concentration was observed in the CP-UA in this study. An increasing winter-spring O 3 and increasing association of high ozone with winter haze events were found in the North China Plain [39].…”

“…3b), the seasonal averages of the O 3 concentrations in the CP-UA during 2017-2020 in spring, summer, autumn, and winter were 149.8, 171.2, 131.1, and 160.0 μg/m 3 , respectively. The O 3 concentrations showed a feature of "high in summer and winter, low in spring and autumn" in the CP-UA, which is different from the feature of "high in spring and summer, low in autumn and winter" in the YRD [35]. The meteorological conditions are the important factor that influences the monthly variation of O 3 in the CP-UA.…”

“…This indicated that O 3 in a city can be affected by its neighboring cities. In a previous study, it was found that O 3 concentrations were spatially agglomerated in BTH and PRD, but spatially dispersed in Chengdu-Chonqing [35]. The highest global Moran's I in CP-UA was found in summer (2.59), indicating a strengthening agglomerated distribution of O 3 concentrations.…”

“…The proportion that exceeded the Grade 2 limit during 2017-2020 was 44.3%, 42.5%, 41.0%, and 29.3%, respectively, suggesting the reduction of O 3 pollution in the CP-UA. In other urban agglomerations of China, e.g., BTH, PRD, and YRD, O 3 concentrations also decreased from 2017 to 2020 [35]…”

Temporal and Spatial Distribution of Ozone and Its Influencing Factors in China

“…Nonetheless, this study only considered regional data and did not examine changes on a national scale. This issue was addressed by Liu et al [24], who discovered that O 3 concentrations at a national level are influenced by both natural and human factors, with temperature, NO x , and VOCs being the key elements influencing O 3 emissions. Yang et al [25] analyzed O 3 pollution in 338 Chinese cities over an extended period and observed that O 3 concentrations in eastern China were generally higher than those in western China, with the most severe pollution occurring in the North, East, and Central regions.…”