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Cyclic volatile methyl siloxanes (cVMS) are high production chemicals present in many personal care products. They are volatile, hydrophobic, and relatively long-lived due to slow oxidation kinetics. Evidence from chamber and ambient studies indicates that oxidation products may be found in the condensed aerosol phase. In this work, we use an oxidation flow reactor to produce ~ 100 μg m-3 of organosilicon aerosol from OH oxidation of decamethylcyclopentasiloxane (D5) with aerosol mass fractions (i.e. yields) of 0.2-0.5. The aerosols were assessed for concentration, size distribution, morphology, sensitivity to seed aerosol, hygroscopicity, volatility and chemical composition through a combination of aerosol size distribution measurement, tandem differential mobility analysis, and electron microscopy. Similar aerosols were produced when vapor from solid antiperspirant or from hair conditioner was used as the reaction precursor. Aerosol yield was sensitive to chamber OH, indicating an interplay between oxidation conditions and the concentration of lower volatility species. The D5 oxidation aerosol products were relatively non-hygroscopic, with average hygroscopicity kappa of ~ 0.01, and nearly non-volatile up to 190 °C temperature. Recommended parameters for treatment as a semi-volatile organic aerosol in atmospheric models are provided. [ABSTRACT FROM AUTHOR]

The Multi-Angle Imager for Aerosols (MAIA), supported by NASA and the Italian Space Agency, is planned for launch into space in 2025. As part of its mission goal, outputs from a chemical transport model, the Unified Inputs for Weather Research and Forecasting Model coupled with Chemistry (UI-WRF-Chem), will be used together with satellite data and surface observations for estimating surface PM 2.5 . Here, we develop a method to improve UI-WRF-Chem with surface observations at the U.S. embassy in Ethiopia, one of MAIA's primary target areas in east Africa. The method inversely models the diurnal profile and amount of anthropogenic aerosol and trace gas emissions. Low-cost PurpleAir sensor data are used for validation after applying calibration functions obtained from the collocated data at the embassy. With the emission updates in UI-WRF-Chem, independent validation for February 2022 at several different PurpleAir sites shows an increase in the linear correlation coefficients from 0.1-0.7 to 0.6-0.9 between observations and simulations of the diurnal variation of surface PM 2.5 . Furthermore, even by using the emissions optimized for February 2021, the UI-WRF-Chem forecast for March 2022 is also improved. Annual update of monthly emissions via inverse modeling has the potential and is needed to improve MAIA's estimate of surface PM 2.5 ., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Nitrogen oxides (NO x ) are a key precursor in O 3 formation. Although stringent anthropogenic NO x emission controls have been implemented since the early 2000s in the United States, several rural regions of California still suffer from O 3 pollution. Previous findings suggest that soils are a dominant source of NO x emissions in California; however, a statewide assessment of the impacts of soil NO x emission (SNO x ) on air quality is still lacking. Here we quantified the contribution of SNO x to the NO x budget and the effects of SNO x on surface O 3 in California during summer by using WRF-Chem with an updated SNO x scheme, the Berkeley Dalhousie Iowa Soil NO Parameterization (BDISNP). The model with BDISNP shows a better agreement with TROPOMI NO 2 columns, giving confidence in the SNO x estimates. We estimate that 40.1% of the state's total NO x emissions in July 2018 are from soils, and SNO x could exceed anthropogenic sources over croplands, which accounts for 50.7% of NO x emissions. Such considerable amounts of SNO x enhance the monthly mean NO 2 columns by 34.7% (53.3%) and surface NO 2 concentrations by 176.5% (114.0%), leading to an additional 23.0% (23.2%) of surface O 3 concentration in California (cropland). Our results highlight the cobenefits of limiting SNO x to help improve air quality and human health in rural California.