Secondary Aerosol Components Research Articles

Airborne in situ characterization of dry urban aerosol optical properties around complex topography

In situ data from the 1997 Southern California Ozone Study—NARSTO 2 2 NARSTO, originally the North American Research Strategy for Tropospheric Ozone, is a public/private partnership whose membership spans government, utilities, industry, and academia throughout Canada, Mexico, and the United States. Its primary mission is to coordinate and enhance policy-relevant scientific research and assessment of tropospheric ozone behavior and provides a cross-organization planning process for scientific investigations. were used to describe the aerosol optical properties in an urban area whose aerosol distribution is modified as the aerosols are advected over the surrounding topography. The data consist of measurements made with a nephelometer and absorption photometer onboard the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Pelican aircraft. The cases investigated in this study include vertical profiles flown over coastal sites as well as sites located along some important mountain ranges in southern California. The vertical distribution of the aerosol in the Los Angeles Basin showed a complex configuration, directly related with the local meteorological circulations and the surrounding topography. High spatial and temporal variability in air pollutant concentrations within a relatively small area was found, as indicated by the aerosol scattering and absorption coefficient data. The results suggest that in areas with such complex terrain, a high spatial resolution is required in order to adequately describe the aerosol optical quantities. Principal components analysis (PCA) has been applied to aerosol chemical samples in order to identify the major aerosol types in the Los Angeles Basin. The technique yielded four components that accounted for 78% of the variance in the data set. These were indicative of marine aerosols, urban aerosols, trace elements and secondary aerosol components of traffic emissions and agricultural activities. A Monte Carlo radiation transfer model has been employed to simulate the effects that different aerosol vertical profiles have on the attenuation of solar energy. The cases examined were selected using the results of the PCA and in situ data were used to describe the atmospheric optical properties in the model. These investigations comprise a number of sensitivity tests to evaluate the effects on the results of the location of the aerosol layers as well as the vertical resolution of the Monte Carlo model.

Seasonal Variation of Chemical Composition in Fine Particles at Gosan, Korea

PM2.5 aerosol samples were collected at Gosan in Jeju Island during six intensive measurement periods between November 2001 and August 2003. In order to investigate the chemical composition of fine particles, major ion components, trace elements, and elemental and organic carbon were analyzed. Quite different seasonal characteristic in the chemical composition of fine particles was observed. The concentration of most secondary aerosol components showed a summer minimum and a winter maximum with higher correlation between them at Gosan. This fact clearly reveals the possibility of long-range transport of such pollutants in winter. On the other hand, OC and EC had the highest concentration and good correlation with ion components, such as K+, Ca2+ in fall. It means that biomass burning could significantly influence the ambient fine carbonaceous particulate in fall, which was primarily long-range transported.

Mass-Size Distributions of Particulate Sulfate, Nitrate, and Ammonium in a Particulate Matter Nonattainment Region in Southern Taiwan

Concentrations and distributions of three major water-soluble ion species (sulfate, nitrate, and ammonium) contained in ambient particles were measured at three sampling sites in the Kao-ping ambient air quality basin, Taiwan. Ambient particulate matter (PM) samples were collected in a Micro-orifice Uniform Deposit Impactor from February to July 2003 and were analyzed for water-soluble ion species with an ion chromatograph. The PM1/PM2.5 and PM1/PM10 concentration ratios at the emission source site were 0.73 and 0.53 and were higher than those (0.68 and 0.48) at the background site because there are more combustion sources (i.e., industrial boilers and traffic) around the emission source site. Mass-size distributions of PM NO3 − were found in both the fine and coarse modes. SO4 2− and NH4 + were found in the fine particle mode (PM2.5), with significant fractions of submicron particles (PM1). The source site had higher PM1/PM10 (79, 42, and 90%) and PM1/PM2.5 concentration ratios (90, 58, and 93%) for the three major inorganic secondary aerosol components (SO4 2−, NO3 −, and NH4 +) than the receptor site (65, 27, and 65% for PM1/PM10; 69, 51, and 70% for PM1/PM2.5). Results obtained in this study indicate that the PM1 (submicron aerosol particles) fraction plays an important role in the ambient atmosphere at both emission source and receptor sites. Further studies regarding the origin and formation of ambient secondary aerosols are planned.

Fragmentation study of diastereoisomeric 2‐methyltetrols, oxidation products of isoprene, as their trimethylsilyl ethers, using gas chromatography/ion trap mass spectrometry

The diastereoisomeric 2-methyltetrols, 2-methylthreitol and 2-methylerythritol, were recently reported as major secondary aerosol components in natural forest aerosols and proposed as molecular markers for the photooxidation of isoprene. In this study, we examine the complex electron and methane chemical ionization behaviors of their trimethylsilyl ethers. In order to gain insight into their fragmentation behaviors, threitol and erythritol were studied as model compounds, and deuterium labeling of the trimethylsilyl groups and ion trap MS2 experiments were performed.

Characterization of size-differentiated inorganic composition of aerosols in Mexico City

Abstract Size-differentiated atmospheric aerosol particles were collected during December 2000–October 2001 in Mexico City (19°N, 99°W) using a micro-orifice uniform deposit impactor. Sulfate and ammonium, which were correlated, were major features of the size distributions. The more predominant mode was at 0.32±0.1 μm, aerodynamic diameter. This peak of concentration is likely the result of condensation of secondary aerosol components from the gas phase. During part of the rainy season (April and June), a larger mode was found at 0.56±0.2 μm, aerodynamic diameter. This peak of concentration, identified as a droplet mode, is probably the result of aqueous-phase reactions (i.e., oxidation of sulfur dioxide in liquid droplets). During August, the peak of concentration was observed at both size ranges of the accumulation mode. Overall, ion balances were achieved with a small deficit of cations, except for the April and June samples, where a significant amount of excess sulfate was present as a result of moderate–high activity of the neighboring volcano Popocatepetl, as well as ambient conditions that favored production of sulfate (moderate–high relative humidity values). Based on the analysis of the ammonia/sulfate molar ratios, the ammonia concentrations were sufficient to fully neutralize sulfate concentrations, except for the April and June samples. During these months, ammonium bisulfate, letovicite and H 2 SO 4(aq) (or a solution of the corresponding ions) were the dominant form of sulfate present in both fine and coarse modes. The acidic nature of these particles (with NH 3 /H 2 SO 4 molar ratio less than 2) is potentially important in assessing health effects of inhaled particles.

The Global Distribution of Secondary Particulate Matter in a 3-D Lagrangian Chemistry Transport Model

A global 3-D Lagrangian chemistry-transport model STOCHEM is used to describe the tropospheric distributions of four components of the secondary atmospheric aerosol: nitrate, sulphate, ammonium and organic compounds. The model describes the detailed chemistry of the formation of the acid precursors from the oxidation of SO2, DMS, NOx, NH3 and terpenes and their uptake into the aerosol. Model results are compared in some detail with the available surface observations. Comparisons are made between the global budgets and burdens found in other modelling studies. The global distributions of the total mass of secondary aerosols have been estimated for the pre-industrial, present day and 2030 emissions and large changes have been estimated in the mass fractions of the different secondary aerosol components.

Observations of aerosol-bound ionic compositions at Cheju Island, Korea

To investigate the regional cycle of aerosols and their ionic constituents, three field intensive campaigns were conducted during fall and winter of 1997 and spring of 1998. The concentrations of most ionic species were found to decrease significantly across fall, winter, and spring such that the sum for all cation (and anion) species of each season is computed as: 193>96>73.7 nequiv m −3 (and 240>104>51.5 nequiv m −3). To examine the fundamental characteristics of aerosol compositions in the study area, we conducted correlation analysis in various manners. The results indicated that the concentrations of major ionic species were strongly affected by some meteorological parameters including wind speed. It was also seen that relative strengths of correlations between important parameters (e.g., between wind speed and most of major inorganic species) maintain close relationships with the factors associated with the air mass origin. In addition, the results of factor analysis indicated the existence of at least three major sources in the study area which include: sea-salt aerosol, secondary aerosol, and organic aerosol component. The springtime occurrence of unexpectedly low concentrations of most ionic constituents is found to sensitively reflect the influence of the inflow of southeasterly winds that prevailed during spring, while it is not common for that season of the year. Because most of those changes are closely tied with the variabilities in the regional circulation patterns for each measurement period, assessment of the ionic composition in concert with the temporal variations of meteorological conditions provided valuable insights into the source signals of different air masses that passed by the study area.

Regional modelling of particulate matter with MADE

Describes the development and application of an aerosol model for regional air quality simulations. The aerosol model MADE is based on a modal concept and describes the chemical composition and the size distribution of atmospheric particulate matter. Primary as well as secondary aerosol components are considered in the model, which is fully integrated into the photochemical transport model EURAD. The model system has been applied to a European domain with different resolutions, using a one‐way nesting procedure. Simulations show the potential importance of secondary organics of anthropogenic and biogenic origin for the tropospheric particle loading. In addition it is shown that a reduction in precursor emissions for the inorganic ion fraction of PM (sulphate, nitrate and ammonium) does not necessarily lead to an equivalent reduction in PM2.5 mass concentrations, as for example a reduction in sulphate aerosol caused by reduced SO2 emissions might be compensated by enhanced formation of nitrate aerosols in certain regions.