Changes in concentration of nitrogen-containing compounds in 10 nm particles of boreal forest atmosphere at snowmelt

Abstract

Measurements to clarify the chemical composition and especially the nitrogen compounds in 10nm ultrafine aerosol particles were carried out at the boreal forest site at the SMEAR II station, Hyytiälä, Finland, during spring–summer–autumn of 2010 and in spring 2011. In 2011, laser aerosol mass spectrometer (laser AMS) provided in-situ chemical composition data for 10nm particles. Laser AMS results, for samples collected in 2011, were clarified through comparison with findings for partly published 30nm and all-sized particles from filter samples analyzed by chromatographic techniques, re-analysis of the selected 30nm filter samples for quinoline identification by LC–MS and modified results from previously published atmospheric pressure interface time-of-flight mass spectrometer (APi-TOFMS) data. The chemistry of the atmosphere was found to change markedly in mid April 2011, just after snow melt: the concentrations of 35% of the laser AMS ions and compounds determined in 30nm particles from filter samples clearly increased or decreased at this time. Notably, the amount of nitrogen compounds increased and the amount of aldehydes decreased. The laser AMS results for 10nm aerosol samples demonstrated the tendency for nitrogen-containing compounds and oxygenated and non-oxygenated hydrocarbons to increase in concentration after snow melt. More detailed analysis confirmed that the two most interesting, frequently observed, and abundant laser AMS ions, m/z 143 and 185, originated from 1-(X-methylquinolin-X-yl) ethanone. According to laser AMS and APi-TOFMS data, when the quinoline concentrations in the 10nm particulate phase increased, the concentrations in the molecular clusters decreased, indicating changes in the partitioning between particle and gas phases.