Relation Between Optical And Chemical Properties Of Ambient Aerosols:Field Study By Single Particle Mass Spectrometry In Shanghai

Recently, atmospheric aerosol draws much attention because of its impact on human health, air quality, visibility and climate. The optical properties of aerosols govern their interaction with sunlight and are generally required as important parameters for estimating radioactive forcing in model studies. The particle number concentration, size distribution, hygroscopicity, chemical composition and mixing state have a huge influence on its optical properties. Aerosol time-of-fright mass spectrometer (ATOFMS) provides single particle size and chemical composition information in real time. Cavity ring down aerosol extinction spectrometer (CRD-AES) and nephelometer are deployed for real-time measuring aerosol optical properties, such as light extinction, absorption, scattering coefficients and single scattering albedo. By using these technologies, we have conducted an extensive analysis of aerosol number concentration, size distribution, chemical composition, mixing state and their relation with particle optical properties in winter Shanghai. Understanding of the regional characterization of optical properties of ambient aerosol helps to reduce the uncertainty in estimating aerosol radiative forcing.This thesis focuses on the following two topics:(1) Particle classification in data analysis. It is difficult to distinguish primary and secondary particle type with complicated mixing state in such huge amount data collected by ATOFMS, so we need effective classification methods. By ART-2a classification combined with source apportionment and size information, we compared different mass spectrometric features and distinguish the particle types clearly. Compared with ART-2a classification, marker classification method is applied much earlier and more widely. Using marker method, combined with previous studies and parameter (such as m/z、area and relative area) selection in programming language, total particles will be divided into several categories: mineral dust aerosols(Dust), sea salt aerosols(Sodium),carbonaceous aerosols (Carbon), biomass burning aerosols and secondary aerosols (including sulfate, nitrate, ammonium and organic).(2) Relation between aerosol chemical composition, mixing state and optical properties. Regional measurements of aerosol physical, optical and chemical properties have been conducted in winter Shanghai. The absorption properties on workdays display diurnal variation of two peaks with two peaks due to traffic emissions and nocturnal inversion layer. There was a relative good correlation between size distributions of submicron aerosols with light extinction coefficients (R2=0.6). Correlation coefficients (R2) with the aerosol light scattering and absorption coefficient (at532nm) of aged OC and ECOC class particles are over0.5. The mixing state of these particles varied with the optical properties; the peak areas of nitrate and ammonium marker ions have a significant enhancement in haze events. It was observed that secondary species, such as ammonium, nitrate, and sulfate were internally mixed with all the primary particle type. The calculated correlation coefficients between the aerosol scattering coefficients and relative intensity of sulfate and nitrate particles were0.30and0.39. The number fraction of fresh EC showed a strong reverse correlation with single scattering albedo (R2=0.7). Other aerosol classes including dust, sea salt, industrial emission, fresh EC and fresh OC showed a weak correlation with aerosol optical properties.