Organic Components Containing Sulfur and Nitrogen Reduce the Volatility of Urban Organic Aerosols

QIAORONG XIE, Alexander Laskin, Pingqing Fu, Purdue University

     Abstract Number: 363
     Working Group: Urban Aerosols

Abstract
Size-segregated samples of atmospheric organic aerosol (OA) in the urban area of Beijing were collected near the ground surface (8 m) and at 260 m above the ground provided by a meteorological tower. The OA samples were analyzed by ultrahigh-resolution Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry with electrospray ionization source operated in negative mode. Substantial contributions of oxygenated organics, organosulfates and nitrooxy-organosulfates with broad range of molecular weights were detected in all samples. Assessment of the aerosol volatility representative of the size-segregated samples was performed. The results show that collected OA samples were dominated by extremely low, ultralow, and non-volatility organic compounds, and their volatility decreases with particle size, particularly at the episodes of severe air pollution. During the haze events, OA samples collected at 260 m height in the urban boundary layer contained more aged, lower volatility, species likely formed throughout regional transport, than those found in the ground-level OA samples. The reactions of oxygen-containing compounds with sulfur dioxide and nitrogen oxides resulted in formation of much low volatility products with nitrooxy-organosulfates being the most non-volatile components. We estimate for the first time the vapor pressure changes with the presence of organosulfates and nitrooxy-organosulfates in size-segregated aerosol particles. Our study demonstrates the importance of these low-volatility organic compounds in the urban boundary layer, which is crucial for modeling their physicochemical properties and ageing evolution in troposphere.