Field Studies Of Aerosol Optical And Chemical Properties In Shanghai

Aerosol is one of the most important components in the atmosphere and plays an important role in the global climate, regional atmospheric pollution and human health. Nowadays, PM2.5 (particulate matter with diameter smaller than 2.5 μm) has been one of the hottest focuses of the public in China, since the Chinese people are keeping suffering from the widely enveloped heavy haze days. However, the sources of the high concentration of PM2.5 and their impacts on the visibility is not yet clear. In this paper, a suite of instruments with high time-resolution, such as ATOFMS (Aerosol Time-Of-Flight Mass Spectrometer), CRDS (Cavity Ring-Down Spectroscopy), Nephelometer, and MARGA (Monitor for AeRosols and Gases), is deployed to follow the evolution of aerosol’s chemical components and optical properties during three independent periods in Shanghai urban area, aiming to resolve the questions, such as the main sources of aerosol in Shanghai urban area, the basic aerosol optical properties, and the influences from chemical components and particle mixing states on aerosol optical properties. As one of the important components in organic carbon aerosol, particulate amine is also studied. The conclusions are:(1) Locally emitted particles have smaller diameters and higher particulate acidity, compared with those larger (but still fine) and less acidic particles transported through northwestern area in Shanghai. The fresh particle types are mainly from local emissions, while the regionally transported particles are deeply aged, with more particulate ammonium and nitrate.(2) High concentration of particulate matters contribute to a significant increase of aerosol bulk extinction coefficient, but the chemical components and particle mixing states determine the extinction efficiency. Deeply aged particles containing a large amount of light scattering materials, such as ammonium, nitrate and sulfate, can enhance particle’s light scattering efficiency, while more particulate organic carbon components could impair the scattering efficiency. The diurnal pattern of elemental carbon signals from vehicle emitted elemental carbon/organic carbon particles has a negative correlation with the single scattering albedo (SSA). In clean days, the number fraction of high mass organic carbon particles presents a well negative correlation with SSA, probably due to the particulate aromatic and nitro-aromatic materials that are light absorbing; while in polluted days, the correlation is not clear since the large amount of light scattering materials in particles could have changed the light absorbing efficiency.(3) Observation with high time-resolution reveals the continuous change of aerosol chemical components, particle types, and particle mixing states and the mass extinction efficiency is largely determined by the mixing states of the aerosol.(4) Temperature, relative humidity (RH), and particulate acidity are three main factors that control the number fraction of amine particles. Low ambient temperature, high RH, and strong particulate acidity can guarantee more particulate amine.