Compositional variations of sea-salt-mode aerosol particles from the North Atlantic

Individual sea-salt-mode aerosol particles collected during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) experiment in June 1992 were studied using transmission electron microscopy in both imaging and analysis modes. The set of eight samples provided an opportunity to compare ''clean,'' ''intermediate,'' and ''dirty'' oceanic aerosols. In the clean samples, major species include NaCl, mixed-cation (Na, Mg, K, and Ca) sulfates, and in some particles, NaNO3. The same compounds also occur in intermediate samples, but compositional groups can be distinguished that are characterized by low- and high-Cl losses from sea salt. In these samples, most Cl loss is compensated by NaNO3 formation. Several compositional groups occur in the dirty samples; these include, in addition to the particle types in clean and intermediate samples, Na2SO4 (with minor Mg, K, and Ca), (NH4)(2)SO4, and silicates. The uniform compositions of sea-salt-mode particles in the clean samples suggest that the same process was acting on all particles. Their excess sulfate and nitrate probably formed through the oxidation of SO2 in the sea-salt aerosol water and by reactions between NOx and NaCl. On the other hand, distinct compositional groups in the dirty samples reveal that long-range transport of continental air masses resulted in the mixing of aerosols that were exposed to different conditions. In addition to O-3 oxidation, cloud processing may have contributed to the formation of excess sulfate in these samples

Soot and sulfate aerosol particles in the remote marine troposphere

Sulfate aerosol particles containing soot aggregates were observed in the marine troposphere in both hemispheres under conditions that ranged from extremely clean to heavily polluted. Even in clean air above the remote Southern Ocean during the First Aerosol Characterization Experiment (ACE 1), depending on the sample, between 10 and 45% of sulfate particles contained soot inclusions. We identified aircraft emissions and biomass burning as the most likely major sources of soot. Internally mixed soot and sulfate appear to comprise a globally significant fraction of aerosols in the troposphere. Anthropogenic combustion aerosols can thus potentially change the radiative climate effects of sulfate aerosols and may have an impact on cloud properties even in the remote troposphere

The geochemical cycling of reactive chlorine through the marine troposphere

Heterogeneous reactions involving sea‐salt aerosol in the marine troposphere are the major global source for volatile inorganic chlorine. We measured reactant and product species hypothesized to be associated with these chemical transformations as a function of phase, particle size, and altitude over the North Atlantic Ocean during the summer of 1988. Concentrations of HCl were typically less than 1.0 ppbv near the sea surface and decreased with altitude and with distance from the U.S. east coast. Concentrations of Cl volatilized from aerosols were generally equivalent to the corresponding concentrations of HCl and ranged from less than detection limits to 125 nmol m−3 STP. Highest absolute and percentage losses of particulate Cl were typically associated with elevated concentrations of anthropogenic combustion products. Concentrations of product nss SO42− and N03− in coarse aerosol fractions indicate that on average only 38% of measured Cl− deficits could be accounted for by the combined effects of acid‐base desorption and reactions involving nonacidic N gases. We hypothesize a mechanism for the Cl loss initiated by reaction of O3 at sea‐salt aerosol surfaces, generating Cl2 followed by rapid photochemical conversion of Cl2 to HCl via Cl atoms (Cl˙) and eventual recapture of HCl by the aerosol. Simulations with a zero‐dimension (0‐D) photochemical model suggest that oxidation by Cl˙ may be an important tropospheric sink for dimethyl sulfide and hydrocarbons. Under low‐NOx conditions, the rapid cycling of reactive Cl would provide a catalytic loss mechanism for O3, which would possibly explain the low O3 concentrations often observed above the world\u27s oceans

The Effect of Coherence and Multiple Scattering on Laser Radar Air Pollution Measurements

179 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1971.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD