Source apportionment of PM2.5 nitrate and sulfate in China using a source-oriented chemical transport model

Abstract

Nitrate and sulfate account for a significant fraction of PM2.5 mass and are generally secondary in nature. Contributions to these two inorganic aerosol components from major sources need to be identified for policy makers to develop cost effective regional emission control strategies. In this work, a source-oriented version of the Community Multiscale Air Quality (CMAQ) model that directly tracks the contributions from multiple emission sources to secondary PM2.5 is developed to determine the regional contributions of power, industry, transportation and residential sectors as well as biogenic sources to nitrate and sulfate concentrations in China in January and August 2009.The source-oriented CMAQ model is capable of reproducing most of the available PM10 and PM2.5 mass, and PM2.5 nitrate and sulfate observations. Model prediction suggests that monthly average PM2.5 inorganic components (nitrate + sulfate + ammonium ion) can be as high as 60 μg m−3 in January and 45 μg m−3 in August, accounting for 20–40% and 50–60% of total PM2.5 mass. The model simulations also indicate significant spatial and temporal variation of the nitrate and sulfate concentrations as well as source contributions in the country. In January, nitrate is high over Central and East China with a maximum of 30 μg m−3 in the Sichuan Basin. In August, nitrate is lower and the maximum concentration of 16 μg m−3 occurs in North China. In January, highest sulfate occurs in the Sichuan Basin with a maximum concentration of 18 μg m−3 while in August high sulfate concentration occurs in North and East China with a similar maximum concentration. Power sector is the dominating source of nitrate and sulfate in both January and August. Transportation sector is an important source of nitrate (20–30%) in both months. Industry sector contributes to both nitrate and sulfate concentrations by approximately 20–30%. Residential sector contributes to approximately 10–20% of nitrate and sulfate in January but its contribution is low in August.