Insights into submicron particulate evolution, sources and influences on haze pollution in Beijing, China

Abstract

The real-time continuous measurements of non-refractory submicron aerosol (NR-PM1) species including organics (Org), sulfate (SO42−), nitrate (NO3−), ammonium (NH4+) and chloride (Cl−) in winter from 10 December 2015 to 30 January 2016 in Beijing were performed with an Aerodyne Aerosol Chemical Speciation Monitor (ACSM). The average concentration of NR-PM1 was 81.24 μg m−3, with the mean concentration in heavy haze days being 220.00 μg m−3, ∼3 times higher than that in light haze days and ∼15 times higher than that in clean days. Org was the most significant component of NR-PM1 species, accounting for 53% of the total NR-PM1 for the entire study. SO42− was also a significant component, accounting for 23% of the total NR-PM1. However, NO3−, NH4+ and Cl− composition together accounted for 25% of the total NR-PM1. All NR-PM1 species presented remarkably diurnal cycles in haze days, characterized by the highest concentrations occurring at midnight, and the lowest concentrations occurring at daytime. Note that the sulfur oxidation ratios were higher than the nitrogen oxidation ratios for the entire study, especially during the haze periods. The formation of sulfate was mainly affected by relative humidity (RH), while that of nitrate was more associated with NH3. Heterogeneous oxidation of NO2 on the surfaces of aerosol particles might be a significant pathway of nitrate formations during haze periods. NR-PM1 was mainly from secondary chemical reactions contributing 46.1%, vehicle emissions contributing 22.3%, coal combustion contributing 16.1%, and biomass burning contributing 15.6% in clean days. However, compared to the clean-day source contributions, the haze-day secondary source contribution to NR-PM1 increased to 66.8%, indicating that NR-PM1 in haze days was dramatically dominated by the secondary pollutants.