Hygroscopicity and optical properties of alkylaminium sulfates

Source identification and characterization of organic nitrogen in atmospheric aerosols at a suburban site in China

Despite the fact that atmospheric particulate organic nitrogen (ON) can significantly affect human health, ecosystems and the earth's climate system, qualitative and quantitative chemical characterization of ON remains limited due to its chemical complexity. In this study, the Aerodyne soot particle - high-resolution time-of-flight aerosol mass spectrometer (SP-AMS) was deployed for ambient measurements in Nanjing, China. Positive matrix factorization (PMF) was applied to the ON data to quantify the sources of ON in submicron aerosols. The averaged ON concentration was 1.24 μg m^-3, while the averaged total nitrogen (TN) in the aerosol was 20.26 μg m^-3. From the PMF ON analysis, a 5-factor solution was selected as the most representative and interpretable solution for the investigated dataset, including oxygenated OA (OOA_ON), amine-related OA_ON (AMOA_ON), hydrocarbon-like OA (HOA_ON), industry OA (IOA_ON), and local primary OA (POA_ON) factors. The quantified ON ions were separated into families, including C_xHN, C_xH_yNO, C₃H_<6N, C_xH_2x+2N, C_xH_2xN and Others, consistent with their contribution to each factor. The C_xH_yNO family mainly contributed to the OOA_ON factor and suggested the presence of amides or amino acids. The C_xH_2x+2N family likely mostly originated from amines only contributing to the AMOA_ON and HOA_ON factors. The IOA_ON and POA_ON factors were resolved due to significant tracers in the mass spectra. Further, compared with regular organic PMF analysis, PMF ON analysis gave more insights due to improved source separation and interpretability of the OA components, which could be a role model for further atmospheric ON research.

Molecular properties affecting the hydration of acid-base clusters

In the atmosphere, water in all phases is ubiquitous and plays important roles in catalyzing atmospheric chemical reactions, participating in cluster formation and affecting the composition of aerosol particles. Direct measurements of water-containing clusters are limited because water is likely to evaporate before detection, and therefore, theoretical tools are needed to study hydration in the atmosphere. We have studied thermodynamics and population dynamics of the hydration of different atmospherically relevant base monomers as well as sulfuric acid-base pairs. The hydration ability of a base seems to follow in the order of gas-phase base strength whereas hydration ability of acid-base pairs, and thus clusters, is related to the number of hydrogen binding sites. Proton transfer reactions at water-air interfaces are important in many environmental and biological systems, but a deeper understanding of their mechanisms remain elusive. By studying thermodynamics of proton transfer reactions in clusters containing up to 20 water molecules and a base molecule, we found that that the ability of a base to accept a proton in a water cluster is related to the aqueous-phase basicity. We also studied the second deprotonation reaction of a sulfuric acid in hydrated acid-base clusters and found that sulfate formation is most favorable in the presence of dimethylamine. Molecular properties related to the proton transfer ability in water clusters are discussed.

Single Usage of a Kitchen Degreaser Can Alter Indoor Aerosol Composition for Days

To the best of our knowledge, this study represents the first observation of multiday persistence of an indoor aerosol transformation linked to a kitchen degreaser containing monoethanol amine (MEA). MEA remaining on the cleaned surfaces and on a wiping paper towel in a trash can was able to transform ammonium sulfate and ammonium nitrate into (MEA)₂SO₄ and (MEA)NO₃. This influence persisted for at least 60 h despite a high average ventilation rate. The influence was observed using both offline (filters, impactors, and ion chromatography analysis) and online (compact time-of-flight aerosol mass spectrometer) techniques. Substitution of ammonia in ammonium salts was observed not only in aerosol but also in particles deposited on a filter before the release of MEA. The similar influence of other amines is expected based on literature data. This influence represents a new pathway for MEA exposure of people in an indoor environment. The stabilizing effect on indoor nitrate also causes higher indoor exposure to fine nitrates.