Distinct seasonality in vertical variations of tropospheric ozone over coastal regions of southern China

The surface ozone pollution is strongly coupled with ozone variations above the ground. Using sufficient airborne ozone profiles during 2012-2018, this study reveals the tropospheric ozone distributions over four cities located in coastal regions of southern China. The 7-year mean tropospheric ozone profiles in the four cities consistently show a double-maxima profile, with a local maximum at 1 km altitude and the other in the middle-to-upper troposphere. Seasonally, springtime ozone is larger than the annual mean throughout the troposphere, while ozone in summer is high in the middle-to-upper troposphere, leading to largest vertical variations among seasons. Ozone in the middle-to-upper troposphere is lower in autumn than in spring and summer. The winter ozone is characterized with a minimum in the lower troposphere, and low values in the middle-to-upper troposphere, leading to least vertical variations among seasons. We untangle the causes for these complicated vertical ozone variations using the GEOS-Chem model. The tropospheric ozone over southern China is partitioned into locally produced ozone, regionally transported native ozone, imported ozone from outside of China (foreign ozone) and natural stratospheric ozone. The results suggest that the springtime ozone abundance is due to the enhanced import of foreign and stratospheric ozone and the intensified regional transport processes of native ozone. In summer, local ozone production is enhanced and regional transport of ozone in the middle-to-upper troposphere is strengthened due to upward air motions, while such transport becomes weaker in autumn leaving low ozone in the middle-to-upper troposphere. In winter, the intensive westerly jets promote foreign and stratospheric ozone again in the middle-to-upper troposphere, but the local ozone production and regional transport are sharply reduced, resulting in low ozone near the surface. This study provides new insights into regional ozone profiles and reveals the significance of vertical ozone variations on surface ozone prevention strategy.

Marginal Damage of Methane Emissions: Ozone Impacts on Agriculture

Methane directly contributes to air pollution, as an ozone precursor, and to climate change, generating physical and economic damages to different systems, namely agriculture, vegetation, energy, human health, or biodiversity. The methane-related damages to climate, measured as the Social Cost of Methane, and to human health have been analyzed by different studies and considered by government rulemaking in the last decades, but the ozone-related damages to crop revenues associated to methane emissions have not been incorporated to policy agenda. Using a combination of the Global Change Analysis Model and the TM5-FASST Scenario Screening Tool, we estimate that global marginal agricultural damages range from ~423 to 556 $2010/t-CH4, of which 98 $2010/t-CH4 occur in the USA, which is the most affected region due to its role as a major crop producer, followed by China, EU-15, and India. These damages would represent 39-59% of the climate damages and 28-64% of the human health damages associated with methane emissions by previous studies. The marginal damages to crop revenues calculated in this study complement the damages from methane to climate and human health, and provides valuable information to be considered in future cost-benefits analyses.

Ambient ozone over mid-Brahmaputra Valley, India: effects of local emissions and atmospheric transport on the photostationary state

This study presents the characteristics of ground level atmospheric ozone (O₃) over the rural mid-Brahmaputra Valley region of the northeastern India. Ozone and oxides of nitrogen (NO_x = NO + NO₂) concentration data were obtained from continuous measurement of O₃ and NO_x housed at the MAPAN-AQM station at Tezpur University. The meteorological parameters were obtained from the same station. The diel, monthly, and seasonal variations of O₃ were studied. The O₃-NO_x photostationary state (PS) was carefully examined and it was found that the net O₃ concertation deviated substantially from the PS during the winter season. The deviation could be attributed to local biomass burning, biogenic VOC emission from forest and agriculture, and long-range transport of peroxyacyl nitrate (PAN). The long-range transport has been ascertained by examining the ventilation coefficients (VC), which correlated with the steep growth of net O₃ concentrations in the morning hours. The HYSPLIT air mass back trajectories were used in concentration-weighted trajectory (CWT) analyses of O₃ to assess the long-range regional transport of O₃ precursors, which positively influenced local O₃ concentrations.

Residence time analysis of photochemical buildup of ozone in central eastern China from surface observation at Mt. Tai, Mt. Hua, and Mt. Huang in 2004

Using data from surface observation, backward trajectories, and residence time analysis, the amounts of regional photochemical ozone buildup due to the large-scale anthropogenic sources in central eastern China (CEC, 30.5-40.5 N, 112.5-122.5 E) at Mt. Tai, Mt. Hua, and Mt. Huang in 2004 were quantified. It was found that the CEC anthropogenic sources influenced the air masses and the associated ozone production most at Mt. Tai, located at the center of CEC domain. At Mt. Hua to the west of CEC domain and at Mt. Huang to the south of CEC domain, the air masses and the associated ozone production showed less CEC anthropogenic influences on a regional scale. At Mt. Tai and Mt. Huang, the ozone mixing ratios in the air masses that passed over polluted source regions in CEC increased during the first 40-70 h after arrival and showed the highest production rate of 31.2 and 12.2 ppb/day, respectively, in May and June. It was estimated that the CEC anthropogenic sources contributed 34-42% of ozone at Mt. Tai and 8-14% at Mt. Huang during this ozone peak season. The large contributions from CEC sources during fall season (Sep-Nov) were also estimated as 31-44 and 17-23% but with the lower ozone production rate of 22.6 and 8.4 ppb/day, respectively, for Mt. Tai and Mt. Huang.