Hygroscopicity of dimethylaminium-, sulfate-, and ammonium-containing nanoparticles

<p>Dimethylamine (DMA) and sulfuric acid (SA) are the important constituents of atmospheric aerosols. To accurately predict the behavior of DMA-containing aerosol systems, exact thermodynamic models are needed. The applicability of these models needs to be tested carefully in different experimental settings to continuously validate and improve their performance. In this work, the Extended Aerosol Inorganics Model (E-AIM) was used to simulate the hygroscopicity of aerosol particles generated from five different aqueous DMA-SA solutions. The applicability of the model was tested in the 10–200 nm size range and from DMA-SA molar ratios ranging from 1:3 to 2:1. The aerosol hygroscopic growth at 0–80% RH was determined with two tandem differential mobility analyzers, and the composition of the generated particles was measured with the Aerosol Mass Spectrometer (AMS), which revealed that the particles contained also ammonium. The model accurately captured the hygroscopicity for particles larger than 80 nm. With particles smaller than 80 nm, the model underestimated the hygroscopicity in all the studied experimental conditions. An increase in hygroscopicity parameter <i>κ</i> with decreasing particle size implied a plausible base evaporation in the experimental setup, which in turn may have affected the modeled hygroscopicity as the composition of the smallest particles may have differed from the AMS measurements. Coupling E-AIM to a dynamic evaporation model, however, could not produce compositions whose modeled hygroscopic behavior would match the measured hygroscopic growth at smaller sizes. Our results, therefore, suggest that DMA thermodynamics are not modeled correctly in E-AIM or there exists uncertainty in the physicochemical parameters.</p> <p>© 2018 American Association for Aerosol Research</p

Effect of Pellet Boiler Exhaust on Secondary Organic Aerosol Formation from α‑Pinene

Interactions between anthropogenic and biogenic emissions, and implications for aerosol production, have raised particular scientific interest. Despite active research in this area, real anthropogenic emission sources have not been exploited for anthropogenic-biogenic interaction studies until now. This work examines these interactions using α-pinene and pellet boiler emissions as a model test system. The impact of pellet boiler emissions on secondary organic aerosol (SOA) formation from α-pinene photo-oxidation was studied under atmospherically relevant conditions in an environmental chamber. The aim of this study was to identify which of the major pellet exhaust components (including high nitrogen oxide (NO_<i>x</i>), primary particles, or a combination of the two) affected SOA formation from α-pinene. Results demonstrated that high NO_<i>x</i> concentrations emitted by the pellet boiler reduced SOA yields from α-pinene, whereas the chemical properties of the primary particles emitted by the pellet boiler had no effect on observed SOA yields. The maximum SOA yield of α-pinene in the presence of pellet boiler exhaust (under high-NO_<i>x</i> conditions) was 18.7% and in the absence of pellet boiler exhaust (under low-NO_<i>x</i> conditions) was 34.1%. The reduced SOA yield under high-NO<i>_x</i> conditions was caused by changes in gas-phase chemistry that led to the formation of organonitrate compounds

Aerosol Chemical Composition in Cloud Events by High Resolution Time-of-Flight Aerosol Mass Spectrometry

This study presents results of direct observations of aerosol chemical composition in clouds. A high-resolution time-of-flight aerosol mass spectrometer was used to make measurements of cloud interstitial particles (INT) and mixed cloud interstitial and droplet residual particles (TOT). The differences between these two are the cloud droplet residuals (RES). Positive matrix factorization analysis of high-resolution mass spectral data sets and theoretical calculations were performed to yield distributions of chemical composition of the INT and RES particles. We observed that less oxidized hydrocarbon-like organic aerosols (HOA) were mainly distributed into the INT particles, whereas more oxidized low-volatile oxygenated OA (LVOOA) mainly in the RES particles. Nitrates existed as organic nitrate and in chemical form of NH₄NO₃. Organic nitrates accounted for 45% of total nitrates in the INT particles, in clear contrast to 26% in the RES particles. Meanwhile, sulfates coexist in forms of acidic NH₄HSO₄ and neutralized (NH₄)₂SO₄. Acidic sulfate made up 64.8% of total sulfates in the INT particles, much higher than 10.7% in the RES particles. The results indicate a possible joint effect of activation ability of aerosol particles, cloud processing, and particle size effects on cloud formation

Real-Time Chemical Composition Analysis of Particulate Emissions from Woodchip Combustion

Residential wood combustion is one of the major sources of fine particles. The chemical composition of the particles plays a key role in both adverse health and environmental effects. It is important to understand how chemical composition of particulate emissions varies during different combustion processes and conditions. In this work, combustion of wood chips was studied in a moving step-grate burner in different combustion conditions (efficient, intermediate, and smoldering) in the laboratory. The particulate emissions were measured with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS). It was found that two phases were occurring frequently in the intermediate and smoldering combustion. Phase 1 took place when gaseous carbon monoxide (CO) was rapidly increasing after the new fuel addition. Phase 2 was a stable, burn-out period with low CO emissions until the new fuel addition and automatic removal of fuel leftovers from the grate. The analysis on the organic aerosol by positive matrix factorization (PMF) extracted out five factors: hydrocarbon-like organic aerosol (HOA), low-volatile-oxidized organic aerosol (LV-OOA), biomass burning organic aerosol (BBOA), and two additional factors of “polycyclic aromatic hydrocarbon (PAH) factor” and “aromatic factor”. PAH and LV-OOA were found to be forming mainly during phase 1. HOA showed similar behavior as a PAH factor and LV-OOA in a time series. BBOA was consistent with levoglucosan formation during the combustion and became higher during phase 2. The aromatic factor was mainly composed of fragment ions of <i>n</i>-butyl benzenesulfonamide compound, which was observed in both phases. To our knowledge, this is the first work to report the particulate organics of combustion aerosols and PAH distinguished by PMF. The results prove that the particulate organic emissions can be reduced efficiently when keeping combustion efficiency high. This may help in targeting the efforts on emission reduction better in the future