NO3 radical production from the reaction between the Criegee intermediate CH2OO and NO2.

Formation of the NO3 radical was observed following photolysis of the CH2I2 + O2 system at 248 nm under ambient atmospheric boundary layer conditions (~760 Torr and 297 K) in the presence of NO2. The Criegee intermediate (CI) CH2OO is believed to be responsible for the NO3 production. The potential of such reactions to enhance the rate of NO3 production in the atmosphere is discussed.

Molecular composition of boreal forest aerosol from Hyytiälä, Finland, using ultrahigh resolution mass spectrometry.

Organic compounds are important constituents of fine particulate matter (PM) in the troposphere. In this study, we applied direct infusion nanoelectrospray (nanoESI) ultrahigh resolution mass spectrometry (UHR-MS) and liquid chromatography LC/ESI-UHR-MS for the analysis of the organic fraction of PM1 aerosol samples collected over a two week period at a boreal forest site (Hyytiälä), southern Finland. Elemental formulas (460-730 in total) were identified with nanoESI-UHR-MS in the negative ionization mode and attributed to organic compounds with a molecular weight below 400. Kendrick Mass Defect and Van Krevelen approaches were used to identify compound classes and mass distributions of the detected species. The molecular composition of the aerosols strongly varied between samples with different air mass histories. An increased number of nitrogen, sulfur, and highly oxygenated organic compounds was observed during the days associated with continental air masses. However, the samples with Atlantic air mass history were marked by a presence of homologous series of unsaturated and saturated C12-C20 fatty acids suggesting their marine origin. To our knowledge, we show for the first time that the highly detailed chemical composition obtained from UHR-MS analyses can be clearly linked to meteorological parameters and trace gases concentrations that are relevant to atmospheric oxidation processes. The additional LC/ESI-UHR-MS analysis revealed 29 species, which were mainly attributed to oxidation products of biogenic volatile compounds BVOCs (i.e., α,ß-pinene, Δ3-carene, limonene, and isoprene) supporting the results from the direct infusion analysis.