Real-time physiochemistry of urban aerosols during a regional haze episode by a single-particle aerosol mass spectrometer: Mixing state, size distribution and source apportionment

Özet

Regional haze pollution can normally be divided into four stages comprising pre-accumulation, explosion,duration and dissipation, under which the physiochemical characteristics of aerosols were clearly distinct. In thisstudy, the chemical compositions and mixing state of aerosols and their source apportionments during a regionalhaze pollution process in the North China Plain (NCP) were comparably discussed for the different haze evolutionstages. Six main particle groups were identified, including carbon-rich particles (53.17%), K-rich particles(27.41%), heavy-metal particles (10.9%), sodium particles (5.61%), dust particles (1.62%) and ammoniumparticles (1.29%). Subsequently, the chemical components and size distributions of aerosols were found to varyduring the different haze stages. Contrary to the OCEC, K–CN, Cu and Pb particles, the EC-nitrate, EC-secondaryand Fe particle groups had increasing proportions with the development of the haze events. The fraction of Kparticles was higher during the pre-accumulation stage and descended rapidly during the subsequent hazestages. In contrast to the OCEC particles, the EC-nitrate and EC-secondary particles from 0.6 to 1.2 μm increasedsignificantly with haze deterioration, implying the enhancement (decline) of aged (primary) carbonaceousparticles during the haze episode. The source contributions of PM2.5 changed with the evolution of the hazeevents, with the largest percentage up to 52.23% from residual and industry emissions during the explosionstage. In contrast to industry and direct combustion emissions, the aging process and traffic emission contributedincreasingly with the aggravation of the haze episodes, with higher fractions of 33.17% and 15.57%, respectively,throughout the duration stage.