Local and regional contributions to fine particulate matter in the 18 cities of Sichuan Basin, southwestern China

Abstract

Abstract. The Sichuan Basin (SCB) is one of the regions suffering from severe air pollution in China, but fewer studies have been conducted for this region than for the more developed regions in eastern and northern China. In this study, a source-oriented version of the Community Multiscale Air Quality (CMAQ) model was used to quantify contributions from nine regions to PM2.5 (i.e., particulate matter, PM, with an aerodynamic diameter less than 2.5 µm) and its components in the 18 cities within the SCB in the winter (December 2014 to February 2015) and summer (June to August 2015). In the winter, citywide average PM2.5 concentrations are 45–126 µg m−3, with 21 %–51 % and 39 %–66 % being due to local and nonlocal emissions, respectively. In the summer, 15 %–45 % and 25 %–52 % of citywide average PM2.5 (14–31 µg m−3) are due to local and nonlocal emissions, respectively. Compared to primary PM (PPM), the inter-region transport of secondary inorganic aerosols (SIA), including ammonia, nitrate, and sulfate ions (NH4+, NO3-, and SO42-, respectively), and their gas-phase precursors are greater. The region to the east of SCB (R7, including central and eastern China and others) is the largest contributor outside the SCB, and it can contribute approximately 80 % of PM2.5 in the eastern, northeastern, and southeastern rims of the SCB but only 10 % in other SCB regions in both seasons. Under favorable transport conditions, regional transport of air pollutants from R7 could account for up to 35–100 µg m−3 of PM2.5 in each of the SCB cities in the winter. This study demonstrates that it is important to have joint emission control efforts among cities within the SCB and regions to the east in order to reduce PM2.5 concentrations and prevent high PM2.5 days for the entire basin.

Elucidating the pollution characteristics of nitrate, sulfate and ammonium in PM<sub>2.5</sub> in Chengdu, southwest China, based on 3-year measurements

“…This finding also indicates that the instability of local pollutant emissions and regional transport during cold months was affected by meteorological conditions (Li et al, 2017;Ji et al, 2018). The large variation amplitude of pollutants in different months, similar to the changes in the Beijing-Tianjin-Hebei region of northern China and Chengdu, is due to the accumulation and removal of pollution by meteorological conditions and pollutant emissions (Ji et al, 2019;Qin et al, 2019;.…”

Severe air pollution events not avoided by reduced anthropogenic activities during COVID-19 outbreak

“…It should be declared that out of the benchmark does not mean failure of the prediction as the benchmark value is constructed on the MM5 simulations for the eastern United States with finer grid resolutions (12 km and 4 km). The WRF model predictions are normally reliable since the model performance statistics are like other WRF studies applied over China (Zhang et al, 2012a;Qiao et al, 2019;Hu et al, 2016). Tables S2 and S3 show the model performance statistics of PM 2.5 from the two emission reduction cases.…”

Relative effects of open biomass burning and open crop straw burning on haze formation over central and eastern China: modeling study driven by constrained emissions

“…However, the NMBs were within a reasonable range (> −25 %) during EP1 but presented much lower values (> 40 %) during the other periods. Thus, this demonstrates that original OBB emissions as well as other sources can allow the model to capture spatiotemporal variations in PM 2.5 concentrations for normal situations without significant impacts by OBB in most of the provinces, as recorded by previous studies (Hu et al, 2015;Liu et al, 2016;Qiao et al, 2019), whereas the model failed to reproduce the rapid outbreak of PM 2.5 concentrations for this OBB event, especially during EP2 in Henan and Anhui. This result shows the need to derive optimal OBB emissions using this constraining method.…”

“…Open crop straw burning (OCSB), as a crucial part of OBB, generally occurs on a large spatial scale during the harvest seasons in regions with intensive agricultural activities, because it is still the most effective, efficient, and economical measure to dispose of open crop straw (Li et al, 2007;Qin and Xie, 2011;Zhang et al, 2017Zhang et al, , 2018Zhang et al, , 2019Xu et al, 2019). Previous studies showed that emissions from OCSB accounted for more than 80 % of those from OBB over China during the past decade.…”