Organic aerosol components observed in Northern Hemispheric datasets from Aerosol Mass Spectrometry

Abstract

In this study we compile and present results from the factor analysis of 43 Aerosol Mass Spectrometer (AMS) datasets (27 of the datasets are reanalyzed in this work). The components from all sites, when taken together, provide a holistic overview of Northern Hemisphere organic aerosol (OA) and its evolution in the atmosphere. At most sites, the OA can be separated into oxygenated OA (OOA), hydrocarbon-like OA (HOA), and sometimes other components such as biomass burning OA (BBOA). We focus on the OOA components in this work. In many analyses, the OOA can be further deconvolved into low-volatility OOA (LV-OOA) and semi-volatile OOA (SV-OOA). Differences in the mass spectra of these components are characterized in terms of the two main ions <i>m/z</i> 44 (CO<sub>2</sub><sup>+</sup>) and <i>m/z</i> 43 (mostly C<sub>2</sub>H<sub>3</sub>O<sup>+</sup>), which are used to develop a new mass spectral diagnostic for following the aging of OA components in the atmosphere. The LV-OOA component spectra have higher <i>f</i><sub>44</sub> (ratio of <i>m/z</i> 44 to total signal in the component mass spectrum) and lower <i>f</i><sub>43</sub> (ratio of <i>m/z</i> 43 to total signal in the component mass spectrum) than SV-OOA. A wide range of <i>f</i><sub>44</sub> and O:C ratios are observed for both LV-OOA (0.17±0.04, 0.73±0.14) and SV-OOA (0.07±0.04, 0.35±0.14) components, reflecting the fact that there is a continuum of OOA properties in ambient aerosol. The OOA components (OOA, LV-OOA, and SV-OOA) from all sites cluster within a well-defined triangular region in the <i>f</i><sub>44</sub> vs. <i>f</i><sub>43</sub> space, which can be used as a standardized means for comparing and characterizing any OOA components (laboratory or ambient) observed with the AMS. Examination of the OOA components in this triangular space indicates that OOA component spectra become increasingly similar to each other and to fulvic acid and HULIS sample spectra as <i>f</i><sub>44</sub> (a surrogate for O:C and an indicator of photochemical aging) increases. This indicates that ambient OA converges towards highly aged LV-OOA with atmospheric oxidation. The common features of the transformation between SV-OOA and LV-OOA at multiple sites potentially enable a simplified description of the oxidation of OA in the atmosphere. Comparison of laboratory SOA data with ambient OOA indicates that laboratory SOA are more similar to SV-OOA and rarely become as oxidized as ambient LV-OOA, likely due to the higher loadings employed in the experiments and/or limited oxidant exposure in most chamber experiments

Gas–particle partitioning of atmospheric aerosols: interplay of physical state, non-ideal mixing and morphology

“…6 Such effects are especially important for systems containing SOA of moderate to lower hygroscopicity (a first-order proxy of which is an atomic oxygen-to-carbon (O : C) ratio below B0.8). 8,11 Since SOA of moderate to lower hygroscopicity forms frequently in the atmosphere, [32][33][34] liquidliquid phase separation needs to be accounted for in atmospheric models of detailed gas-particle processes. Parameterizations aiming at computational efficiency, while considering the RH-dependency of liquid-liquid and liquid-solid phase transitions, are needed for the development of next-generation air quality and chemistry-climate models.…”

Role of the reaction of stabilized Criegee intermediates with peroxy radicals in particle formation and growth in air

“…2,4 SOA is produced by atmospheric oxidation of volatile organic compounds (VOCs) that can lead to the formation of products having sufficiently low vapor pressures to either nucleate to form new particles or condense onto pre-existing particles. 5,6 At present, however, a quantitative understanding of SOA formation from such oxidation processes remains limited, resulting in large uncertainties in predicting the impacts of organic aerosol on air quality, climate and human health.…”

PM1 Chemical Characterization during the ACU15 Campaign, South of Mexico City

“…The HOA factor is compared to the HOA factor found during MILAGRO, where the ion series C n H + 2n+1 and C n H 2+ 2n−1 (which includes m/z 41, 43, 55, 57) are distinguishable. The two OOA factors are compared to the one OOA factor found during MILAGRO, where the ion at m/z 44 (CO 2 + ) is predominant [40].…”

“…The OOA contribution to the organic mass (SV-OOA + LV-OOA = 78%) is larger during ACU15 than during MILAGRO (OOA 46%), even including BBOA (16%), due to the importance of the LV-OOA. The triangle plot described by Ng et al [40] can be of further help to classify the organic components described above. The analysis uses ions m/z 44 and m/z 43 as a diagnostic for the aging of the OA.…”