Browsing by Subject "cloud condensation nuclei"
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Item Chemical and Physical Properties of Atmospheric Aerosols (a) A Case Study in the Unique Properties of Agricultural Aerosols (b) The Role of Chemical Composition in Ice Nucleation during the Arctic Spring(2011-08-08) Moon, Seong-GiThis study focuses on the analysis of atmospheric particles sampled from two different field campaigns: the field study at a cattle feeding facility in the summer from 2005 to 2008 and the Indirect and Semi-Direct Aerosol Campaign (ISDAC) in 2008. A ground site field study at a representative large cattle feeding facility in the Texas Panhandle was conducted to characterize the particle size distributions, hygroscopicity, and chemical composition of agricultural aerosols. Here, a first comprehensive dataset is reported for these physical and chemical properties of agricultural aerosols appropriate for use in a site-specific emission inventory. The emission rate and transport of the aerosols are also discussed. In addition, mixing ratios of total and gaseous ammonia were measured at the same field in 2007 and 2008. Measurements such as these provide a means to determine whether the fugitive dust emitted from a typical large feedlot represents a health concern for employees of the feeding operation and the nearby community. Detailed chemical composition of aircraft-sampled particles collected during ISDAC was studied. Filter samples were collected under a variety of conditions in and out of mixed phase and ice clouds in the Arctic. Specifically, particles were sampled from a mixed-phase cloud during a period of observed high concentrations of ice nuclei (IN), a biomass plume, and under relatively clean ambient conditions. Composition of particles was studied on a particle-by-particle basis using several microspectroscopy techniques. Based on the elemental composition analysis, more magnesium was found in Arctic cloud residues relative to ambient air. Likewise, based on the carbon speciation analysis, high IN samples contained coated inorganics, carbonate, and black or brown carbon particles. In the samples collected during a flight through a biomass burning plume, water-soluble organic carbon was the dominant overall composition. Due to their hygroscopic nature, these organics may preferably act as cloud condensation nuclei (CCN) rather than IN. Other ambient samples contained relatively higher fractions of organic and inorganic mixtures and less purely water-soluble organics than found in the biomass particles. The most likely source of inorganics would be sea salt. When present, sea salt may further enhance ice nucleation.Item Chemical Composition and Cloud Nucleation Ability of Marine Aerosol(2013-12-12) Deng, ChunhuaThis study is focused on the chemical composition and cloud nucleation ability of marine aerosol based on two cruise researches over Pacific Ocean and North Atlantic Ocean respectively. Implications of CLAW hypothesis and the factors influencing its validity are analyzed for the contemporary era with ever-increasing pollution. The pacific cruise started from Punta Arenas, Chile and ended in Seattle, WA during March-April of 2010. Raman microspectroscopy (RMS) was employed to identify the chemical composition and mixing conditions of single particles collected. By analyzing multiple particles in a collected ensemble, the degree of external/internal mixing of particles was also determined. Atmospheric aerosol concentration, cloud condensation nuclei (CCN) concentration, and chlorophyll a concentration in the underlying water (a metric for phytoplankton biomass in the ocean), were also measured. Our results indicate that long chain organic molecules were prevalent in the marine aerosol samples throughout the cruise. Long chain organic compounds tended to stay mixed with other organic and inorganic components. The influence of marine organic aerosols on cloud nucleation ability is analyzed. The North Atlantic cruise started from Woods Hole, MA and returned back to the same location during June-July 2011. The cruise passed through a wide range of conditions, including areas of high phytoplankton biomasses and extremely high DMS levels (over 1800 pptv). Aerosol concentration, cloud condensation nuclei (CCN) concentration, particle size distribution, as well as surface seawater and atmospheric DMS concentrations were performed simultaneously during the cruise. HYSPLIT back trajectories were used to classify air mass origins. Even though continental sources increased the total aerosol population, it depressed the effective CCN concentrations possibly due to the competition in particle growth. Continuous high CCN and elevated DMS concentrations over the open ocean occur concurrently, which can be explained by enhanced nucleation and condensational growth of aerosols in marine boundary layer (MBL) resulting from the DMS oxidation or primary aerosols from the sea surface. Our data also indicated that uncertainties remain in sea spray aerosol production flux function, especially for particles with dry diameter smaller than 200 nm.