China's Clean Air Action has suppressed unfavorable influences of climate on wintertime PM<sub>2.5</sub> concentrations in Beijing since 2002

Abstract

25 30 35 40 Atmos. Chem. Phys. Discuss., https://doi.Abstract Severe wintertime PM2.5 pollution in Beijing has been receiving increasing worldwide attention, yet the decadal variations remain relatively unexplored. Combining field measurements and 45 model simulations, we quantified the relative influences of anthropogenic emissions and meteorological conditions on PM2.5 concentrations in Beijing over winters of 2002-2016. Between the winters of 2011 and 2016, stringent emission control measures resulted in a 21% decrease in mean mass concentrations of PM2.5 in Beijing, with 7 fewer haze days per winter on average. With fixed emissions, meteorological conditions over the study period would have 50 led to an increase of haze in Beijing, but the strict emission control measures have suppressed the unfavorable influences of recent climate. The unfavorable meteorological conditions are attributed to the weakening of the East Asia Winter Monsoon associated particularly with an increase in pressure associated with the Aleutian low. 55 60 65Atmos. Chem. Phys. Discuss., https://doi.

Recent Isotopic Evidence for Elevated Vehicular NOx Emission to Atmospheric Nitrate Formation in Chinese Megacities

“…A significant decrease in PM 2.5 concentrations was observed nationwide during this period, which proves the benefits of the implementation of the Clean Air Actions since 2013. 17,19,34 In contrast, the NO 3 − concentrations have not decreased as expected in certain cities (e.g. Nanjing and Hangzhou; Figure 1), despite a considerable decrease (national average of 21%) in the mixing ratios of its precursor, NOx.…”

“…To address the severe air pollution issues, the Chinese government has implemented a series of stringent clean air actions nationwide since 2013. − Benefiting from these strategies, the national emissions of NOx decreased by 21% (2013–2017) as estimated by the MEIC model . Among these strategies, strengthening vehicle emission standards were calculated to be a prominent contributor to NOx abatements (e.g., 1.06 Tg, 13% of all national abatements), while strengthening industrial emission standards was the most effective for NOx abatements (4.77 Tg, 60% of all national abatements) .…”

Air quality and climate change, Topic 3 of the Model Inter-Comparison Study for Asia Phase III (MICS-Asia III) – Part 2: aerosol radiative effects and aerosol feedbacks

“…Aerosols change weather and climate via the following pathways: they absorb and scatter solar and thermal radiation to alter the radiative balance of the earth-atmosphere system (Gao et al, 2019b;Liu et al, 2011;Jia et al, 2018), which is referred to as direct effects, and they serve as cloud condensation nuclei (CCN) and/or ice nuclei (IN) to modify cloud properties, which is referred to as indirect effects (Haywood and Boucher, 2000). The suppression of cloud convection induced by direct effects of absorbing aerosols is known as the semidirect effect Lohmann and Feichter, 2005).…”