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1. Isoprene Emissions Response to Drought and the Impacts on Ozone and SOA in China

   https://doi.org/10.1029/2020JD033263  

   Wang, Peng; Liu, Yiming; Dai, Jianing; Fu, Xiao; Wang, Xuemei; Guenther, Alex; Wang, Tao (May 2021, Journal of Geophysical Research: Atmospheres)

   Abstract Among the various environmental factors that affect isoprene emissions, drought has only been given limited attention. Four different drought response (DR) schemes were implemented in the Model of Emissions of Gases and Aerosols from Nature (MEGAN, version 2.1), and the Community Multiscale Air Quality (CMAQ) model was applied to investigate the drought impacts on air quality during both drought and normal years in China. Generally, all DR schemes decrease isoprene emissions except for mild drought conditions. The significant decrease and even termination of isoprene emissions are predicted in South China under severe drought conditions. During the drought period, the DR scheme considering both mild and severe drought (SMD) improves the model performance especially in severe drought‐hit regions when compared with the Ozone Monitoring Instrument (OMI) averaged formaldehyde vertical column density (HCHO VCD). The results show that most of the DR schemes decrease simulated ozone (O₃) and secondary organic aerosols (SOA) levels. For both O₃and SOA, noticeable changes are predicted in the Sichuan Basin (5 ppb and 4 µg m⁻³for O₃and SOA, respectively). This investigation is the first modeling study to investigate the impacts of isoprene drought response on air quality in China. 

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2. Changes in the Relative Importance of Biogenic Isoprene and Soil NOx Emissions on Ozone Concentrations in Nonattainment Areas of the United States

   https://doi.org/10.1029/2021JD036361  

   Geddes, Jeffrey A.; Pusede, Sally E.; Wong, Anthony Y. H. (July 2022, Journal of Geophysical Research: Atmospheres)

   Abstract Reductions in anthropogenic emissions have drawn increasing attention to the role of the biosphere in O₃production chemistry in U.S. cities. We report the results of chemical transport model sensitivity simulations exploring the relative impacts of biogenic isoprene and soil nitrogen oxides (NOx) emissions on O₃and its temporal variability. We compare scenarios with high and low anthropogenic NOx emissions representing the reductions that have occurred in recent decades. As expected, summertime O₃concentrations become less sensitive to perturbations in biogenic isoprene emissions as anthropogenic NOx emissions decline. However, we demonstrate for the first time that across policy relevant O₃nonattainment areas of the United States, O₃becomes more sensitive to perturbations in soil NOx emissions than to identical perturbations in isoprene emissions. We show that interannual variability in soil NOx emissions may now have larger impacts on interannual O₃variability than isoprene emissions in many areas where the latter would have dominated in the recent past. 

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3. On Recent Large Antarctic Ozone Holes and Ozone Recovery Metrics

   https://doi.org/10.1029/2021GL095232  

   Stone, K. A.; Solomon, S.; Kinnison, D. E.; Mills, Michael J. (November 2021, Geophysical Research Letters)

   Abstract The 2015 and 2020 ozone holes set record sizes in October–December. We show that these years, as well as other recent large ozone holes, still adhere to a fundamental recovery metric: the later onset of early spring ozone depletion as chlorine and bromine diminishes. This behavior is also captured in the Whole Atmosphere Chemistry Climate Model. We quantify observed recovery trends of the onset of the ozone hole and in the size of the September ozone hole, with good model agreement. A substantial reduction in ozone hole depth during September over the past decade is also seen. Our results indicate that, due to dynamical phenomena, it is likely that large ozone holes will continue to occur intermittently in October–December, but ozone recovery will still be detectable through the later onset, smaller, and less deep September ozone holes: metrics that are governed more by chemical processes. 

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4. Have improvements in ozone air quality reduced ozone uptake into plants?

   https://doi.org/10.1525/elementa.399  

   Ronan, Allison C.; Ducker, Jason A.; Schnell, Jordan L.; Holmes, Christopher (January 2020, Elem Sci Anth)
5. Explicit modeling of isoprene chemical processing in polluted air masses in suburban areas of the Yangtze River Delta region: radical cycling and formation of ozone and formaldehyde

   https://doi.org/10.5194/acp-21-5905-2021  

   Zhang, Kun; Huang, Ling; Li, Qing; Huo, Juntao; Duan, Yusen; Wang, Yuhang; Yaluk, Elly; Wang, Yangjun; Fu, Qingyan; Li, Li (January 2021, Atmospheric Chemistry and Physics)

   Abstract. In recent years, ozone pollution has become one of the most severeenvironmental problems in China. Evidence from observations have showedincreased frequency of high O3 levels in suburban areas of the YangtzeRiver Delta (YRD) region. To better understand the formation mechanism oflocal O3 pollution and investigate the potential role of isoprenechemistry in the budgets of ROx (OH+HO2+RO2) radicals,synchronous observations of volatile organic compounds (VOCs), formaldehyde(HCHO), and meteorological parameters were conducted at a suburban site ofthe YRD region in 2018. Five episodes with elevated O3 concentrationsunder stagnant meteorological conditions were identified; anobservation-based model (OBM) with the Master Chemical Mechanism was appliedto analyze the photochemical processes during these high O3 episodes.The high levels of O3, nitrogen oxides (NOx), and VOCs facilitatedstrong production and recycling of ROx radicals with the photolysis ofoxygenated VOCs (OVOCs) being the primary source. Our results suggest thatlocal biogenic isoprene is important in suburban photochemical processes.Removing isoprene could drastically slow down the efficiency of ROx recyclingand reduce the concentrations of ROx. In addition, the absence of isoprenechemistry could further lead to a decrease in the daily average concentrationsof O3 and HCHO by 34 % and 36 %, respectively. Therefore, thisstudy emphasizes the importance of isoprene chemistry in the suburbanatmosphere, particularly with the participation of anthropogenic NOx.Moreover, our results provide insights into the radical chemistry thatessentially drives the formation of secondary pollutants (e.g., O3 andHCHO) in suburban areas of the YRD region. 

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