ALBERT

Description: The occurrence of non-liquid and liquid physical states of submicron atmospheric particulate matter (PM) downwind of an urban region in central Amazonia was investigated. Measurements were conducted during two Intensive Operating Periods (IOP1 and IOP2) that took place during the wet and dry seasons, respectively, of the GoAmazon2014/5 campaign. Air masses representing variable influences of background conditions, urban pollution, and regional and continental scale biomass burning passed over the research site. As the air masses varied, particle rebound fraction, which is an indicator of the mix of physical states in a sampled particle population, was measured in real time at ground level using an impactor apparatus. Micrographs collected by transmission electron microscopy confirmed that liquid particles adhered while non-liquid particles rebounded. Relative humidity (RH) was scanned to collect rebound curves. When the apparatus RH matched ambient RH, 95 % of the particles were liquid as a campaign average, although this percentage dropped to as low as 60 % during periods of anthropogenic influence. Secondary organic material, produced for the most part by the oxidation of volatile organic compounds emitted from the forest, was the largest source of liquid PM. Analyses of the mass spectra of the atmospheric PM by positive-matrix factorization (PMF) and of concentrations of carbon monoxide, total particle number, and oxides of nitrogen were used to identify time periods affected by anthropogenic influences, including both urban pollution and biomass burning. The occurrence of non-liquid PM correlated with these indicators of anthropogenic influence. A linear model having as output the rebound fraction and as input the PMF factor loadings explained up to 70 % of the variance in the observed rebound fractions. Anthropogenic influences appear to favor non-liquid PM by providing molecular species that increase viscosity when internally mixed with background PM, by contributing non-liquid particles in external mixtures of PM, and a by combination of these effects under real-world conditions.

Description: Aerosol absorption is strongly dependent on the internal heterogeneity (mixing state) and morphology of individual particles containing black carbon (BC) and other non-absorbing species. Here, we examine an extensive microscopic data set collected in the California central valley during the CARES 2010 field campaign. During a period of high photochemical activity and pollution buildup, the particle mixing state and morphology were characterized using Scanning Transmission X-ray Microscopy (STXM) at the carbon K-edge. Observations of compacted BC core morphologies and thick organic coatings at both urban and rural sites provide evidence of the aged nature of particles. Based on the observation of thick coatings and more convex BC inclusion morphology, the contribution of fresh BC emissions at the urban site was relatively small. These measurements of BC morphology and mixing state provide important constraints for the morphological effects on BC optical properties expected in aged urban plumes.

Description: The elemental composition of organic material in environmental samples – including atmospheric organic aerosol, dissolved organic matter, and other complex mixtures – provides insights into their sources and environmental processing. However, standard analytical techniques for measuring elemental ratios typically require large sample sizes (milligrams of material or more). Here we characterize a method for measuring elemental ratios in environmental samples, requiring only micrograms of material, using a Small Volume Nebulizer (SVN). The technique uses ultrasonic nebulization of samples to generate aerosol particles (100–300nm diameter), which are then analyzed using an aerosol mass spectrometer (AMS). We demonstrate that the technique generates aerosol from complex organic mixtures with minimal changes to the elemental composition of the organic and that quantification is possible using internal standards (e.g., NH415NO3). Sample volumes of 2–4uL with total solution concentrations of at least 0.2–g/L form sufficient particle mass for elemental ratio measurement by the AMS, despite only a small fraction (~0.1%) of the sample forming fine particles while the remainder end up as larger droplets. The method was applied to aerosol filter extracts from the field and laboratory, as well as to dissolved organic matter (DOM) from the North Pacific Ocean. In the case of aerosol particles, the mass spectra and elemental ratios from the SVN-AMS agree with those from online AMS sampling; similarly, for DOM, the elemental ratios determined from the SVN-AMS agree with those determined using combustion analysis. The SVN-AMS provides a platform for the rapid quantitative analysis of the elemental composition of complex organic mixtures and non-refractory inorganic salts from microgram samples with applications that include analysis of aerosol extracts, and terrestrial and atmospheric dissolved organic matter.

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in O'Brien, R. E., Ridley, K. J., Canagaratna, M. R., Jayne, J. T., Croteau, P. L., Worsnop, D. R., Budisulistiorini, S. H., Surratt, J. D., Follett, C. L., Repeta, D. J., & Kroll, J. H. Ultrasonic nebulization for the elemental analysis of microgram-level samples with offline aerosol mass spectrometry. Atmospheric Measurement Techniques, 12(3), (2019):1659-1671, doi:10.5194/amt-12-1659-2019.

Description: The elemental composition of organic material in environmental samples – including atmospheric organic aerosol, dissolved organic matter, and other complex mixtures – provides insights into their sources and environmental processing. However, standard analytical techniques for measuring elemental ratios typically require large sample sizes (milligrams of material or more). Here we characterize a method for measuring elemental ratios in environmental samples, requiring only micrograms of material, using a small-volume nebulizer (SVN). The technique uses ultrasonic nebulization of samples to generate aerosol particles (100–300 nm diameter), which are then analyzed using an aerosol mass spectrometer (AMS). We demonstrate that the technique generates aerosol from complex organic mixtures with minimal changes to the elemental composition of the organic material and that quantification is possible using internal standards (e.g., NH154NO3). Sample volumes of 2–4 µL with total solution concentrations of at least 0.2 g L−1 form sufficient particle mass for elemental ratio measurement by the AMS, despite only a small fraction (∼ 0.1 %) of the sample forming fine particles after nebulization (with the remainder ending up as larger droplets). The method was applied to aerosol filter extracts from the field and laboratory, as well as to the polysaccharide fraction of dissolved organic matter (DOM) from the North Pacific Ocean. In the case of aerosol particles, the mass spectra and elemental ratios from the SVN–AMS agree with those from online AMS sampling. Similarly, for DOM, the elemental ratios determined from the SVN–AMS agree with those determined using combustion analysis. The SVN–AMS provides a platform for the rapid quantitative analysis of the elemental composition of complex organic mixtures and non-refractory inorganic salts from microgram samples with applications that include analysis of aerosol extracts and terrestrial, aquatic, and atmospheric dissolved organic matter.

Description: This work was supported by National Oceanic and Atmospheric Administration grant nos. NA13OAR4310072 and NA140AR4310132. Kelsey J. Ridley acknowledges support from the NSF Graduate Research Fellowship Program. Sri Hapsari Budisulistiorini and Jason D. Surratt acknowledges support from the U.S. Environmental Protection Agency award no. 835404, Electric Power Research Institute (EPRI), and National Oceanic and Atmospheric Administration grant no. NA13OAR4310064. Special thanks are due to David Karl and Eric Grabowski, University of Hawaii, for the CHNS elemental analysis of DOM. Daniel J. Repeta acknowledges support from the Gordan and Betty Moore Foundation award 6000 and the Simons Foundation SCOPE award 329108.