Single particle analysis of amines in ambient aerosol in Shanghai

Abstract

Environmental contextAmines, a group of basic organic compounds, play important roles in atmospheric chemistry. We studied their distribution in ambient aerosols at the single particle level, and found that high relative humidity and strong particle acidity can attract more amines from the gas phase to particles. Amines may account for a significant part of organic mass in aerosols in areas with high emissions of sulfur dioxide and nitrogen oxides. AbstractAn aerosol time-of-flight mass spectrometer was deployed in urban Shanghai to analyse amine-containing particles during two separate sampling periods, 1–9 August 2007 and 22–27 December 2009. Amine-containing particles are identified by a mass spectrometric marker at m/z 86 [NCH2(C2H5)2+] and classified into six major particle types to explore their possible origins. The number fraction of amine-containing particles in winter was much higher than in summer (23.4 v. 4.4 %), which can be explained by preferred gas-to-particle partitioning of gaseous amines at lower temperatures. Mass spectrometric patterns show the strong acidity of particles collected in December 2009, suggesting the acid–base reaction pathway might also contribute to the high concentration of amine aerosol in winter. Two fog episodes and two after-rain episodes of amine-containing particle bursts were observed in August 2007. Tightly correlated number fractions of sulfate- and amine-containing particles in all these episodes reveal that high relative humidity greatly enhances particulate amine formation based on acid–base reaction and subsequent particle growth. Our observations suggest that amines may account for significant parts of secondary organic mass in heavily polluted areas.