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- ItemCloud condensation nuclei in polluted air and biomass burning smoke near the mega-city Guangzhou, China – Part 2: Size-resolved aerosol chemical composition, diurnal cycles, and externally mixed weakly CCN-active soot particles(München : European Geopyhsical Union, 2011) Rose, D.; Gunthe, S.S.; Su, H.; Garland, R.M.; Yang, H.; Berghof, M.; Cheng, Y.F.; Wehner, B.; Achtert, P.; Nowak, A.; Wiedensohler, A.; Takegawa, N.; Kondo, Y.; Hu, M.; Zhang, Y.; Andreae, M.O.; Pöschl, U.Size-resolved chemical composition, mixing state, and cloud condensation nucleus (CCN) activity of aerosol particles in polluted mega-city air and biomass burning smoke were measured during the PRIDE-PRD2006 campaign near Guangzhou, China, using an aerosol mass spectrometer (AMS), a volatility tandem differential mobility analyzer (VTDMA), and a continuous-flow CCN counter (DMT-CCNC). The size-dependence and temporal variations of the effective average hygroscopicity parameter for CCN-active particles (κa) could be parameterized as a function of organic and inorganic mass fractions (forg, finorg) determined by the AMS: κa,p=κorg·forg + κinorg·finorg. The characteristic κ values of organic and inorganic components were similar to those observed in other continental regions of the world: κorg≈0.1 and κinorg≈0.6. The campaign average κa values increased with particle size from ~0.25 at ~50 nm to ~0.4 at ~200 nm, while forg decreased with particle size. At ~50 nm, forg was on average 60% and increased to almost 100% during a biomass burning event. The VTDMA results and complementary aerosol optical data suggest that the large fractions of CCN-inactive particles observed at low supersaturations (up to 60% at S≤0.27%) were externally mixed weakly CCN-active soot particles with low volatility (diameter reduction <5% at 300 °C) and effective hygroscopicity parameters around κLV≈0.01. A proxy for the effective average hygroscopicity of the total ensemble of CCN-active particles including weakly CCN-active particles (κt) could be parameterized as a function of κa,p and the number fraction of low volatility particles determined by VTDMA (φLV): κt,p=κa,p−φLV·(κa,p−κLV). Based on κ values derived from AMS and VTDMA data, the observed CCN number concentrations (NCCN,S≈102–104 cm−3 at S = 0.068–0.47%) could be efficiently predicted from the measured particle number size distribution. The mean relative deviations between observed and predicted CCN concentrations were ~10% when using κt,p, and they increased to ~20% when using only κa,p. The mean relative deviations were not higher (~20%) when using an approximate continental average value of κ≈0.3, although the constant κ value cannot account for the observed temporal variations in particle composition and mixing state (diurnal cycles and biomass burning events). Overall, the results confirm that on a global and climate modeling scale an average value of κ≈0.3 can be used for approximate predictions of CCN number concentrations in continental boundary layer air when aerosol size distribution data are available without information about chemical composition. Bulk or size-resolved data on aerosol chemical composition enable improved CCN predictions resolving regional and temporal variations, but the composition data need to be highly accurate and complemented by information about particle mixing state to achieve high precision (relative deviations <20%).
- ItemChemistry of new particle growth in mixed urban and biogenic emissions - Insights from CARES(München : European Geopyhsical Union, 2014) Setyan, A.; Song, C.; Merkel, M.; Knighton, W.B.; Onasch, T.B.; Canagaratna, M.R.; Worsnop, D.R.; Wiedensohler, A.; Shilling, J.E.; Zhang, Q.Regional new particle formation and growth events (NPEs) were observed on most days over the Sacramento and western Sierra foothills area of California in June 2010 during the Carbonaceous Aerosols and Radiative Effect Study (CARES). Simultaneous particle measurements at both the T0 (Sacramento, urban site) and the T1 (Cool, rural site located ~40 km northeast of Sacramento) sites of CARES indicate that the NPEs usually occurred in the morning with the appearance of an ultrafine mode at ~15 nm (in mobility diameter, Dm, measured by a mobility particle size spectrometer operating in the range 10-858 nm) followed by the growth of this modal diameter to ~50 nm in the afternoon. These events were generally associated with southwesterly winds bringing urban plumes from Sacramento to the T1 site. The growth rate was on average higher at T0 (7.1 ± 2.7 nm h−1) than at T1 (6.2 ± 2.5 nm h−1), likely due to stronger anthropogenic influences at T0. Using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), we investigated the evolution of the size-resolved chemical composition of new particles at T1. Our results indicate that the growth of new particles was driven primarily by the condensation of oxygenated organic species and, to a lesser extent, ammonium sulfate. New particles appear to be fully neutralized during growth, consistent with high NH3 concentration in the region. Nitrogen-containing organic ions (i.e., CHN+, CH4N+, C2H3N+, and C2H4N+) that are indicative of the presence of alkyl-amine species in submicrometer particles enhanced significantly during the NPE days, suggesting that amines might have played a role in these events. Our results also indicate that the bulk composition of the ultrafine mode organics during NPEs was very similar to that of anthropogenically influenced secondary organic aerosol (SOA) observed in transported urban plumes. In addition, the concentrations of species representative of urban emissions (e.g., black carbon, CO, NOx, and toluene) were significantly higher whereas the photo-oxidation products of biogenic VOCs (volatile organic compounds) and the biogenically influenced SOA also increased moderately during the NPE days compared to the non-event days. These results indicate that the frequently occurring NPEs over the Sacramento and Sierra Nevada regions were mainly driven by urban plumes from Sacramento and the San Francisco Bay Area, and that the interaction of regional biogenic emissions with the urban plumes has enhanced the new particle growth. This finding has important implications for quantifying the climate impacts of NPEs on global scale.
- ItemSize distribution, mass concentration, chemical and mineralogical composition and derived optical parameters of the boundary layer aerosol at Tinfou, Morocco, during SAMUM 2006(Milton Park : Taylor & Francis, 2017) Kandler, K.; Schütz, L.; Deutscher, C.; Ebert, M.; Hofmann, H.; Jäckel, S.; Jaenicke, R.; Knippertz, P.; Lieke, K.; Massling, A.; Petzold, A.; Schladitz, A.; Weinzierl, B.; Wiedensohler, A.; Zorn, S.; Weinbruch, S.During the SAMUM 2006 field campaign in southern Morocco, physical and chemical properties of desert aerosols were measured. Mass concentrations ranging from 30μgm−3 for PM2.5 under desert background conditions up to 300 000μgm−3 for total suspended particles (TSP) during moderate dust storms were measured. TSP dust concentrations are correlated with the local wind speed, whereasPM10 andPM2.5 concentrations are determined by advection from distant sources. Size distributions were measured for particles with diameter between 20 nm and 500μm (parametrizations are given). Two major regimes of the size spectrum can be distinguished. For particles smaller than 500 nm diameter, the distributions show maxima around 80 nm, widely unaffected of varying meteorological and dust emission conditions. For particles larger than 500 nm, the range of variation may be up to one order of magnitude and up to three orders of magnitude for particles larger than 10μm. The mineralogical composition of aerosol bulk samples was measured by X-ray powder diffraction. Major constituents of the aerosol are quartz, potassium feldspar, plagioclase, calcite, hematite and the clay minerals illite, kaolinite and chlorite. A small temporal variability of the bulk mineralogical composition was encountered. The chemical composition of approximately 74 000 particles was determined by electron microscopic single particle analysis. Three size regimes are identified: for smaller than 500 nm in diameter, the aerosol consists of sulphates and mineral dust. For larger than 500 nm up to 50μm, mineral dust dominates, consisting mainly of silicates, and—to a lesser extent—carbonates and quartz. For diameters larger than 50μm, approximately half of the particles consist of quartz. Time series of the elemental composition show a moderate temporal variability of the major compounds. Calcium-dominated particles are enhanced during advection from a prominent dust source in Northern Africa (Chott El Djerid and surroundings). The particle aspect ratio was measured for all analysed particles. Its size dependence reflects that of the chemical composition. For larger than 500 nm particle diameter, a median aspect ratio of 1.6 is measured. Towards smaller particles, it decreases to about 1.3 (parametrizations are given). From the chemical/mineralogical composition, the aerosol complex refractive index was determined for several wavelengths from ultraviolet to near-infrared. Both real and imaginary parts show lower values for particles smaller than 500 nm in diameter (1.55–2.8 × 10−3i at 530 nm) and slightly higher values for larger particles (1.57–3.7 × 10−3i at 530 nm).