[1] Aircraft measurements during the 2006 Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) are used to examine the influence of shallow cumulus clouds on vertical profiles of aerosol chemical composition, size distributions, and secondary aerosol precursor gases. The data show signatures of convective transport of particles, gases and moisture from near the surface to higher altitudes, and of aqueous-phase production of aerosol mass (sulfate and organics) in cloud droplets and aerosol water. In cloudy conditions, the average aerosol volume concentration at an altitude of 2850 m, above typical cloud top levels, was found to be 34% of that at 450 m; for clear conditions, the same ratio was 13%. Both organic and sulfate mass fractions were on average constant with altitude (around 50%); however, the ratio of oxalate to organic mass increased with altitude (from 1% at 450 m to almost 9% at 3450 m), indicative of the influence of in-cloud production on the vertical abundance and characteristics of secondary organic aerosol (SOA) mass. A new metric termed "residual cloud fraction" is introduced as a way of quantifying the "cloud processing history" of an air parcel. Results of a parcel model simulating aqueous phase production of sulfate and organics reproduce observed trends and point at a potentially important role of SOA production, especially oligomers, in deliquesced aerosols. The observations emphasize the importance of shallow cumulus clouds in altering the vertical distribution of aerosol properties that influence both their direct and indirect effect on climate.Citation: Wonaschuetz, A., A. Sorooshian, B. Ervens, P. Y. Chuang, G. Feingold, S. M. Murphy, J. de Gouw, C. Warneke, and H. H. Jonsson (2012), Aerosol and gas re-distribution by shallow cumulus clouds: An investigation using airborne measurements,

Steam collection devices collecting aerosol particles into liquid samples are frequently used to analyze water-soluble particulate material. The fate of water-insoluble components is often neglected. In this work, we show that fresh soot particles can be suspended into pure water using a steam collection device, the particle-into-liquid sampler (PILS, Weber et al. 2001). The overall collection efficiency of freshly generated soot particles was found to be on the order of 20%. This shows that, depending on the analytic technique employed, the presence of insoluble, and/or hydrophobic particles in liquid samples from steam collection cannot be neglected. Copyright © 2018 The Author(s). Published with license by Taylor & Francis Group, LLC

No abstract

Abstract. Thermal–optical measurement techniques are widely used for the monitoring of carbonaceous aerosols. Although results of different thermal–optical measurement techniques are comparable for total carbon, they can vary widely for values of elemental carbon especially in the presence of brown carbon. Charring of organic material during the inert heating phase of thermal–optical measurements has been found to be a major confounder, but no literature about investigations of structural changes during this process in atmospheric aerosols is available. In a recent study we investigated these structural changes for combustion aerosol standard (CAST) soot. Now we apply this approach to selected atmospheric aerosol filter samples and a subset of eight washed filter samples with low loadings of water-soluble organic carbon (WSOC). To investigate structural changes, Raman spectra were obtained for samples heated to the corresponding temperature levels and gas atmospheres of the EUSAAR2 and NIOSH870 protocols. The temperature levels where changes in the Raman spectra occurred (i.e., changes in structure) varied for different samples. For the washed samples with low WSOC loadings and absence of other water-soluble aerosol components such as inorganic salts, changes in structural ordering and darkening of the samples were not observed. We were able to show for the first time that the darkening of a sample (measured in terms of transmission laser signal) is not necessarily caused by an increase of structural ordering in the sample. Possible transformations at lower temperatures could include a formation of non-graphitic light-absorbing intermediate organic carbon, a release of C−H groups or a decrease of carbonyl groups.

Abstract. Thermal-optical measurement techniques are widely used for the monitoring of carbonaceous aerosols. Although results of different thermal-optical measurement techniques are comparable for total carbon, they can vary widely for values of elemental carbon especially in the presence of brown carbon. Charring of organic material during the inert heating phase of thermal-optical measurements was found to be a major confounder, but no literature about investigations of structural changes during this process in atmospheric aerosols is available. In a recent study we investigated these structural changes for combustion aerosol standard soot (CAST). Now we apply this approach to selected atmospheric aerosol filter samples and a subset of eight washed filter samples with low WSOCs loadings. To investigate structural changes, Raman spectra were obtained for samples heated to the corresponding temperature levels and gas atmospheres of the EUSAAR2 and NIOSH870 protocols. The temperature levels where changes in the Raman spectra occurred (i.e. changes in structure) varied for different samples. For the washed samples with low WSOC loadings and absence of other water soluble aerosol components such as inorganic salts, changes in structural ordering and darkening of the samples were not observed. For all samples, ion chromatography, integrating sphere measurements (yielding black and brown carbon data) and thermal-optical analyses were performed. We were able to show for the first time that the darkening of a sample (measured in terms of transmission laser signal) is not necessarily caused by an increase of structural ordering in the sample. Therefore we suggest that the widely used term charring should be used carefully when the darkening of a sample during thermal-optical measurement procedures is interpreted.