Assessment of regional air quality resulting from emission control in the Pearl River Delta region, southern China

To evaluate the impact of emission control measures on the air quality in the Pearl River Delta (PRD) region of South China, statistic data including atmospheric observations, emissions and energy consumptions during 2006–2014 were analyzed, and a Weather Research and Forecasting - Community Multi-scale Air Quality (WRF-CMAQ) model was used for various scenario simulations. Although energy consumption doubled from 2004 to 2014 and vehicle number significantly increased from 2006 to 2014, ambient SO2, NO2and PM10were reduced by 66%, 20% and 24%, respectively, mainly due to emissions control efforts. In contrast, O3increased by 19%. Model simulations of three emission control scenarios, including a baseline (a case in 2010), a CAP (a case in 2020 assuming control strength followed past control tendency) and a REF (a case in 2020 referring to the strict control measures based on recent policy/plans) were conducted to investigate the variations of air pollutants to the changes in NOx, VOCs and NH3emissions. Although the area mean concentrations of NOx, nitrate and PM2.5decreased under both NOxCAP (reduced by 1.8%, 0.7% and 0.2%, respectively) and NOxREF (reduced by 7.2%, 1.8% and 0.3%, respectively), a rising of PM2.5was found in certain areas as reducing NOxemissions elevated the atmospheric oxidizability. Furthermore, scenarios with NH3emission reductions showed that nitrate was sensitive to NH3emissions, with decreasing percentages of 0–10.6% and 0–48% under CAP and REF, respectively. Controlling emissions of VOCs reduced PM2.5in the southwestern PRD where severe photochemical pollution frequently occurred. It was also found that O3formation in PRD was generally VOCs-limited while turned to be NOx-limited in the afternoon (13:00–17:00), suggesting that cutting VOCs emissions would reduce the overall O3concentrations while mitigating NOxemissions in the afternoon could reduce the peak O3levels.