Significant wintertime PM2.5 mitigation in the Yangtze River Delta, China, from 2016 to 2019: Observational constraints on anthropogenic emission controls

Ambient fine particulate matter (PM2:5) mitigation relies strongly on anthropogenic emission control measures, the actual effectiveness of which is challenging to pinpoint owing to the complex synergies between anthropogenic emissions and meteorology. Here, observational constraints on model simulations allow us to derive not only reliable PM2:5 evolution but also accurate meteorological fields. On this basis, we isolate meteorological factors to achieve reliable estimates of surface PM2:5 responses to both longterm and emergency emission control measures from 2016 to 2019 over the Yangtze River Delta (YRD), China. The results show that long-Term emission control strategies play a crucial role in curbing PM2:5 levels, especially in the megacities and other areas with abundant anthropogenic emissions. The G20 summit hosted in Hangzhou in 2016 provides a unique and ideal opportunity involving the most stringent, even unsustainable, emergency emission control measures. These emergency measures lead to the largest decrease (35 ugm3, 59 %) in PM2:5 concentrations in Hangzhou. The hotspots also emerge in megacities, especially in Shanghai (32 ugm3, 51 %), Nanjing (27 ugm3, 55 %), and Hefei (24 ugm3, 44 %) because of the emergency measures. Compared to the long-Term policies from 2016 to 2019, the emergency emission control measures implemented during the G20 Summit achieve more significant decreases in PM2:5 concentrations (17 ugm3 and 41 %) over most of the whole domain, especially in Hangzhou (24 ugm3, 48 %) and Shanghai (21 ugm3, 45 %). By extrapolation, we derive insight into the magnitude and spatial distribution of PM2:5 mitigation potential across the YRD, revealing significantly additional room for curbing PM2:5 levels.