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Interactions between aerosols and gases in the atmosphere have been the focus of an increasing number of studies in recent years. Here, we focus on aerosol effects on tropospheric ozone that involve meteorological feedbacks induced by aerosol–radiation interactions. Specifically, we study the effects that involve aerosol influences on the transport of gaseous pollutants and on atmospheric moisture, both of which can impact ozone chemistry. For this purpose, we use the UK Earth System Model (UKESM1), with which we performed sensitivity simulations including and excluding the aerosol direct radiative effect (ADE) on atmospheric chemistry, and focused our analysis on an area with a high aerosol presence, namely China. By comparing the simulations, we found that ADE reduced shortwave radiation by 11 % in China and consequently led to lower turbulent kinetic energy, weaker horizontal winds and a shallower boundary layer (with a maximum of 102.28 m reduction in north China). On the one hand, the suppressed boundary layer limited the export and diffusion of pollutants and increased the concentration of CO , SO2 , NO , NO2 , PM2.5 and PM10 in the aerosol-rich regions. The NO/NO2 ratio generally increased and led to more ozone depletion. On the other hand, the boundary layer top acted as a barrier that trapped moisture at lower altitudes and reduced the moisture at higher altitudes (the specific humidity was reduced by 1.69 % at 1493 m on average in China). Due to reduced water vapour, fewer clouds were formed and more sunlight reached the surface, so the photolytical production of ozone increased. Under the combined effect of the two meteorology feedback methods, the annual average ozone concentration in China declined by 2.01 ppb (6.2 %), which was found to bring the model into closer agreement with surface ozone measurements from different parts of China. [ABSTRACT FROM AUTHOR]

The vertical structure of ozone (O 3) and fine particulate matter (FPM) as well as their interactions are important for understanding the atmospheric chemistry process and their impact on climate. Through a ground-based lidar observation during April 18th-May 22nd 2017 and surface measurement during March 1st-May 31st 2017, this study obtained the vertical distribution of O 3 and aerosol extinction coefficient with their correlations during the springtime in the lower troposphere (LT) in Nanjing, eastern China. Surface average O 3 and PM 2.5 concentrations in spring were 39.89 ppb and 41.93 μg m−3. O 3 generally increased with height in the LT, while aerosol extinction coefficient decreased. The correlation between O 3 and aerosol extinction coefficient was −0.32 at 300 m, and 0.34 at 1747.5 m. An on-line coupled model Weather Research and Forecasting with Chemistry (WRF-Chem) was used to analyze the effect of aerosol's radiation feedback on ozone. Aerosol reduced the surface downward shortwave radiation by −25.66 W m−2, and increased the upwelling shortwave radiation at the top of atmosphere by 3.19 W m−2 in urban Nanjing. The photolysis rate of NO 2 and O1D were reduced by −1% and −0.7% near surface and increased by 0.3% and 0.2% at upper LT. Aerosol-included effect also led to a more stable planet boundary layer (PBL), with −0.24 °C and −0.05 m s−1 changes in temperature and wind speed at surface. However, the temperature and wind speed increased by 0.18 °C and 0.13 m s−1 at 1760 m, respectively. O 3 decreased by −3.70% at surface and increased by 0.89% at 2870 m. This study showed that aerosol can affect ozone through altering photolysis rate and atmospheric stability. Aerosol's radiation feedback has a complex effect on the vertical structure of ozone, which leads to ozone decrease near the surface and increase above the aerosol layer. • The vertical structure and the correlation of O 3 and PM 2.5 were analyzed. • O 3 increases with height in the lower troposphere, while aerosol decreases. • PM 2.5 reduces surface O 3 by reducing photolysis rate and increasing PBL stability. • PM 2.5 and O 3 are positive correlated at higher altitudes. [ABSTRACT FROM AUTHOR]

With the rapid urbanization and the implementation of a series of air pollution control measures, significant changes have occurred in the emission of fine particulate matter (PM 2.5), ozone (O 3) precursors, and CO 2 in China. In this study, we comprehensively assess the impact of emission variations on the East Asian Summer Monsoon (EASM) climate from 2008 to 2018 using a regional-chemistry-ecology model RegCM-Chem-YIBs. The investigations indicated a strengthening of the EASM from 2008 to 2018, with all four EASM Indices exhibiting an increase trend ranging from 0.08 to 1.09 per year based on the simulations. Since 2008, alterations in the emissions of PM 2.5 and O 3 precursors in 2013 and 2018 led to a rise in near-surface temperatures in China by 0.5–1.5 K, thereby enhancing the EASM. Conversely, the changed CO 2 emissions, through its influence on radiative balance and altering BVOCs (Biogenic Volatile Organic Compounds) emissions via its effect on vegetation growth, decreased temperatures by 0.5–1.5 K, thus weakening the EASM. However, when considering the combined effects of total emissions changes in PM 2.5 , O 3 precursors, and CO 2 , surface temperatures increased by 0.5–2 K, ultimately strengthening the EASM. In addition, compared to 2013, EASM was strongly enhanced in 2018 due to the notable increase in CO 2 and significant reduction of PM 2.5 and O 3 precursors. Our study underscores the significant influence of variations in PM 2.5 , O 3 precursors, and CO 2 emissions on EASM climate and emphasizes the importance of coordinated governance of air pollution and climate change. • The emissions of PM 2.5 , O 3 , and CO 2 have undergone considerable changes. • The EASM has strengthened from 2008 to 2018. • The variations in PM 2.5 , O 3 , and CO 2 emissions significant influence the EASM. [ABSTRACT FROM AUTHOR]

The China implemented the Clean Air Action Plan (CAAP) in September 2013 to address the pressing air pollution problem. This initiative yielded a noteworthy reduction in PM 2.5 while simultaneously witnessing the O 3 elevation. Here, we used a revised WRF-Chem model to study the drivers (anthropogenic emissions (EMI), meteorological changes (MET)) of decreasing PM 2.5 and increasing O 3 in eastern China across the four seasons from 2014 to 2020, focusing on the response of aerosol-ozone interaction (AOI) to emission reduction (AOI_ER). In contrast to the original version, the model provided more comprehensive feedback of aerosols on O 3 , including radiation effects and heterogeneous chemistry. Our survey showed that EMI was the main factor causing the PM 2.5 decline and O 3 increase. The influence of MET on both O 3 and PM 2.5 exhibited seasonal variations. Compared to 2014, emission reduction during CAAP weakened the inhibition of aerosol radiative effect on meteorological parameters and photolysis rate, causing a rise in surface shortwave radiation (SW), temperature (T 2), planetary boundary layer height (PBLH), wind speed (WS 10), J NO2 , and J O1D throughout the CAAP period. This increased the O 3 by 0.57–2.11 ppb in the four seasons and enhanced the emission-reduction-induced O 3 increase by 22.2%–57.3%. Emission reduction alleviated the summer negative feedback of AOI on PM 2.5 , increasing by 4.61 μg m−3, thereby offsetting the 16.7% emission reduction efficacy. Oppositely, in spring, autumn, and winter, emission reduction weakened the promotion of AOI on PM 2.5 , resulting in a decrease by 2.5–3.12 μg m−3, amplified the emission-reduction-induced PM 2.5 reduction by 8.3%–26.6%. Nitrate and sulfate aerosols generated by heterogeneous chemistry emerged as the primary components driving the alterations in PM 2.5 within the context of emission reduction. Our research emphasized the importance of considering changes in AOI when formulating emission control policies and evaluating their effectiveness. More effective emission policies should focus on comprehensively considering the emissions and the weakened aerosol effects to achieve better air quality and health benefits. • First study on aerosol-ozone interaction (AOI) in relation to emission reduction. • Emission reduction weakened aerosol radiative effect on meteorology and photolysis. • AOI amplified the emission-reduction-induced (ERI) O 3 increase by 22.2%–57.3%. • AOI enhanced ERI PM 2.5 decline by 8.3%–26.6% and offset 16.7% summer cut efficacy. • Nitrate and sulfate emerged as the primary components driving the PM 2.5 alteration. [ABSTRACT FROM AUTHOR]

With the enactment of Air Pollution Action Plan in 2013, the air quality improved in most Chinese cities, except that surface ozone (O 3) increased markedly. Some recent studies have examined this issue and presented controversial opinions, but only focus on summertime ozone increase. This study extends a comprehensive analysis of the influencing factors on China's ozone changes from 2013 to 2017 out of the summer season, combining satellite data, ground measurements and model analyses. The annual trends of air pollutants, e.g., increase in 95th percentile O 3 concentration (+1.4–8.7 μg m−3 yr−1), and decreases in fine particulate matter (PM 2.5 ; −4.0~−7.5 μg m−3 yr−1) and sulfur dioxide (−2.6~−9.7 μg m−3 yr−1) are uncovered by satellite and observational data. Model results show that the attributions of surface O 3 changes from 2013 to 2017 vary spatially and seasonally, and most regions are more affected by emission changes (−9.5–47.0 μg m−3) rather than meteorological changes (−8.1–21.3 μg m−3). In specific regions and seasons, e.g., south/southwestern and eastern China south of 35°N in May and July, the surface O 3 responses to climate variability could have an equal or even greater importance than emission changes. In these major pollution control regions, e.g. northern and mid-eastern China, the precursor emissions control (11–35%) contributes in the same degree as the changes in aerosol effects (35–38%) to surface ozone enhancement in the warm seasons. More scientific emission controls and climate adaptation strategies are required to attain the synergetic control of atmospheric particulate matter and ozone in China. Image 1 • Air pollution trends are uncovered by satellite data and observations. • The attributions of surface O 3 changes are more affected by emission changes. • O 3 response to atmospheric warming is dominant south of 30°N in warm season. • NO x and VOC s control contributed equally as aerosol effect in NCP and East China. [ABSTRACT FROM AUTHOR]