Showing papers on "Particulates published in 2003"

Organic atmospheric particulate material.

Abstract: Carbonaceous compounds comprise a substantial fraction of atmospheric particulate matter (PM). Particulate organic material can be emitted directly into the atmosphere or formed in the atmosphere when the oxidation products of certain volatile organic compounds condense. Such products have lower volatilities than their parent molecules as a result of the fact that adding oxygen and/or nitrogen to organic molecules reduces volatility. Formation of secondary organic PM is often described in terms of a fractional mass yield, which relates how much PM is produced when a certain amount of a parent gaseous organic is oxidized. The theory of secondary organic PM formation is outlined, including the role of water, which is ubiquitous in the atmosphere. Available experimental studies on secondary organic PM formation and molecular products are summarized.

Characterization of organic aerosols emitted from the combustion of biomass indigenous to South Asia

Abstract: [1] Throughout South Asia biomass is commonly used as a fuel source for cooking and heating homes. The smoke from domestic use of these fuels is expected to be a major source of atmospheric particulate matter in the region and needs to be characterized for input in regional source apportionment models and global climate models. Biomass fuel samples including coconut leaves, rice straw, jackfruit branches, dried cowdung patties, and biomass briquettes manufactured from compressed biomass material were obtained from Bangladesh. The fuel samples were burned in a wood stove to collect and characterize the particulate matter emissions. The bulk chemical composition including total organic and elemental carbon, sulfate, nitrate, ammonium and chloride ions, and bulk elements such as potassium and sodium did not show conclusive differences among the biomass samples tested. Unique features, however, exist in the detailed organic characterization of the combustion smoke from the different sources. The organic compound fingerprints of the particulate matter are shown to be distinct from one another and distinct from North American wood fuels. Fecal stanols including 5b-stigmastanol, coprostanol, and cholestanol are found to be good molecular markers for the combustion of cowdung. Additionally, the patterns of methoxyphenols and plant sterols provide a unique signature for each biomass sample and are conducive as source apportionment tracers. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0399 Atmospheric Composition and Structure: General or miscellaneous; 1699 Global Change: General or miscellaneous; KEYWORDS: biomass aerosol, molecular marker, organic

Inorganic bromine in the marine boundary layer: a critical review

Abstract: . The cycling of inorganic bromine in the marine boundary layer (mbl) has received increased attention in recent years. Bromide, a constituent of sea water, is injected into the atmosphere in association with sea-salt aerosol by breaking waves on the ocean surface. Measurements reveal that supermicrometer sea-salt aerosol is substantially depleted in bromine (often exceeding 50%) relative to conservative tracers, whereas marine submicrometer aerosol is often enriched in bromine. Model calculations, laboratory studies, and field observations strongly suggest that the supermicrometer depletions reflect the chemical transformation of particulate bromide to reactive inorganic gases that influence the processing of ozone and other important constituents of marine air. Mechanisms for the submicrometer enrichments are not well understood. Currently available techniques cannot reliably quantify many Br containing compounds at ambient concentrations and, consequently, our understanding of inorganic Br cycling over the oceans and its global significance are uncertain. To provide a more coherent framework for future research, we have reviewed measurements in marine aerosol, the gas phase, and in rain. We also summarize sources and sinks, as well as model and laboratory studies of chemical transformations. The focus is on inorganic bromine over the open oceans outside the polar regions. The generation of sea-salt aerosol at the ocean surface is the major tropospheric source producing about 6.2 Tg/a of bromide. The transport of Br from continents (as mineral aerosol, and as products from biomass-burning and fossil-fuel combustion) can be of local importance. Transport of degradation products of long-lived Br containing compounds from the stratosphere and other sources contribute lesser amounts. Available evidence suggests that, following aerosol acidification, sea-salt bromide reacts to form Br2 and BrCl that volatilize to the gas phase and photolyze in daylight to produce atomic Br and Cl. Subsequent transformations can destroy tropospheric ozone, oxidize dimethylsulfide (DMS) and hydrocarbons in the gas phase and S(IV) in aerosol solutions, and thereby potentially influence climate. The diurnal cycle of gas-phase Br and the corresponding particulate Br deficits are correlated. Higher values of Br in the gas phase during daytime are consistent with expectations based on photochemistry. We expect that the importance of inorganic Br cycling will vary in the future as a function of both increasing acidification of the atmosphere (through anthropogenic emissions) and climate changes. The latter affects bromine cycling via meteorological factors including global wind fields (and the associated production of sea-salt aerosol), temperature, and relative humidity.

Evaluation of elemental carbon as a marker for diesel particulate matter

Abstract: Elemental carbon (EC) in atmospheric particulate matter originates from a broad range of sources in many urban locations. As health and air quality studies are using elemental carbon measurements to better understand the impact of diesel engines and other combustion sources, there is a great need to clearly understand the relative source contributions to EC concentrations in the atmosphere. However, the different analytical techniques currently used to measure EC do not show good agreement for many particulate matter samples. To this end, studies that use EC as a tracer and integrate different analytical techniques for EC can significantly bias estimates of source contributions to atmospheric particulate matter. In addition, source attribution studies that do not properly address all sources of EC in the atmosphere can also lead to inaccuracies and biases. To better understand the use of EC as a tracer, a review of the distribution of EC in the primary particulate matter emissions from air pollution sources using different analytical methods is discussed. A review of previous apportionment studies of particulate matter is presented to elucidate the fraction of EC that results from emissions from diesel engines in urban locations. These results demonstrate that EC is not a unique tracer for diesel exhaust and efforts to utilize EC as an indicator of diesel exhaust must properly address other sources of EC as well as utilize a consistent measurement technique for EC when comparing source and ambient EC measurements to avoid significant biases.

Exposure to particulate matter, volatile organic compounds, and other air pollutants inside patrol cars.

Abstract: People driving in a vehicle might receive an enhanced dose of mobile source pollutants that are considered a potential risk for cardiovascular diseases. The exposure to components of air pollution in highway patrol vehicles, at an ambient, and a roadside location was determined during 25 work shifts (3 p.m. to midnight) in the autumn of 2001, each day with two cars. A global positioning system and a diary provided location and activity information. Average pollutant levels inside the cars were low compared to ambient air quality standards: carbon monoxide 2.7 ppm, nitrogen dioxide 41.7 microg/m3, ozone 11.7 ppb, particulate matter smaller 2.5 microm (PM2.5) 24 microg/m3. Volatile organic compounds inside the cars were in the ppb-range and showed the fingerprint of gasoline. PM2.5 was 24% lower than ambient and roadside levels, probably due to depositions associated with the recirculating air conditioning. Levels of carbon monoxide, aldehydes, hydrocarbons, and some metals (Al, Ca, Ti, V, Cr, Mn, Fe, Cu, and Sr) were highest in the cars, and roadside levels were higher than ambient levels. Elevated pollutant levels were related to locations with high traffic volumes. Our results point to combustion engine emissions from other vehicles as important sources of air pollutants inside the car.

Evaluating the first‐order effect of intraannual temperature variability on urban air pollution

Abstract: [1] The direct effect of intraannual temperature variability on ozone and PM2.5 concentrations at the urban scale was simulated using a high-resolution air quality model that tracks the temperature-dependant formation of secondary organic and inorganic aerosol components. Calculations show that the concentration of ozone and non-volatile secondary particulate matter will generally increase at higher temperatures due to increased gas-phase reaction rates. The concentration of semi-volatile reaction products also will increase at higher temperatures, but the amount of this material that partitions to the particle-phase may decrease as equilibrium vapor pressures rise. Calculations performed for Southern California on September 25, 1996 predict that intraannual temperature variability may cause peak ozone and PM2.5 concentrations to fluctuate by up to 16% and 25% respectively. 24-hour average PM2.5 concentrations will decrease with increasing temperatures for inland portions of the South Coast air basin during most of the day. Slight increases in 24-hour average PM2.5 concentrations were predicted for coastal regions. The majority of the predicted shift in PM2.5 concentrations was related to increased production rates for nitric acid and condensable organic compounds balanced against increased volatilization of these products. Semi-volatile particulate ammonium nitrate concentrations are most sensitive to volatilization losses at hotter temperatures and when the ratio of gas-phase ammonia to nitric acid concentrations is approximately unity. Background sulfate particles and particles released from non-catalyst equipped gasoline-powered engines, diesel engines, and food cooking were shifted to smaller sizes as ammonium nitrate volatilized at hotter temperatures.

Emissions of Trace Gases and Particles from Savanna Fires in Southern Africa

Abstract: Airborne measurements made on initial smoke from 10 savanna fires in southern Africa provide quantitative data on emissions of 50 gaseous and particulate species, including carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen oxides, methane, ammonia, dimethyl sulfide, nonmethane organic compounds, halocarbons, gaseous organic acids, aerosol ionic components, carbonaceous aerosols, and condensation nuclei (CN). Measurements of several of the gaseous species by gas chromatography and Fourier transform infrared spectroscopy are compared. Emission ratios and emission factors are given for eight species that have not been reported previously for biomass burning of savanna in southern Africa (namely, dimethyl sulfide, methyl nitrate, five hydrocarbons, and particles with diameters from 0.1 to 3 microns). The emission factor that we measured for ammonia is lower by a factor of 4, and the emission factors for formaldehyde, hydrogen cyanide, and CN are greater by factors of about 3, 20, and 3 - 15, respectively, than previously reported values. The new emission factors are used to estimate annual emissions of these species from savanna fires in Africa and worldwide.

Air pollution and daily mortality in a city with low levels of pollution.

Abstract: The concentration-response relationship between daily ambient inhalable particle (particulate matter less than or equal to 10 micro m; PM(10)) concentrations and daily mortality typically shows no ...

Concentration gradient patterns of aerosol particles near interstate highways in the Greater Cincinnati airshed

Abstract: The objective of this study was to determine if there is an exposure gradient in particulate matter concentrations for people living near interstate highways, and to determine how far from the highway the gradient extends. Air samples were collected in a residential area of Greater Cincinnati in the vicinity of two major highways. The measurements were conducted at different distances from the highways by using ultrafine particle counters (measurement range: 0.02–1 µm), optical particle counters (0.3–20 µm), and PM2.5 Harvard Impactors (0.02–2.5 µm). The collected PM2.5 samples were analyzed for mass concentration, for elemental and organic carbon, and for elemental concentrations. The results show that the aerosol concentration gradient was most clearly seen in the particle number concentration measured by the ultrafine particle counters. The concentration of ultrafine particles decreased to half between the sampling points located at 50 m and 150 m downwind from the highway. Additionally, elemental analysis revealed a gradient in sulfur concentrations up to 400 m from the highway in a residential area that does not have major nearby industrial sources. This gradient was qualitatively attributed to the sulfate particle emissions from diesel engine exhausts, and was supported by the concentration data on several key elements indicative of traffic sources (road dust and diesel exhaust). As different particulate components gave different profiles of the diesel exposure gradient, these results indicate that no single element or component of diesel exhaust can be used as a surrogate for diesel exposure, but more comprehensive signature analysis is needed. This characterization is crucial especially when the exposure data are to be used in epidemiological studies.

Uptake of nitrate and sulfate on dust aerosols during TRACE-P

Abstract: Aerosol data collected near Asia on the DC-8 aircraft platform during TRACE-P has been examined for evidence of uptake of NO3(-) and SO4(-) on dust surfaces. Data is compared between a sector where dust was predominant and a sector where dust was less of an influence. Coincident with dust were higher mixing ratios of anthropogenic pollutants. HNO3, SO2, and CO were higher in the dust sector than the nondust sector by factors of 2.7, 6.2, and 1.5, respectively. The colocation of dust and pollution sources allowed for the uptake of NO3(-) and nss-SO4(-) on the coarse dust aerosols, increasing the mixing ratios of these particulates by factors of 5.7 and 2.6 on average. There was sufficient nss-SO4(-) to take up all of the NH4(+) present, with enough excess nss-SO4(-) to also react with dust CaCO3. This suggests that the enhanced NO3(-) was not in fine mode NH4NO3. Particulate NO3(-) (p-NO3(-)) constituted 54% of the total NO3(-), (t-NO3(-)) on average, reaching a maximum of 72% in the dust sector. In the nondust sector, p-NO3(-) contributed 37% to t-NO3(-), likely due to the abundance of sea salts there. In two other sectors where the influence of dust and sea salt were minimal, p-NO3(-), accounted for < 15% of t-NO3(-).

Mixture state and size of Asian dust particles collected at southwestern Japan in spring 2000

Abstract: [1] Atmospheric particles were collected at Kumamoto (32°48′N, 130°45′E), a coastal city in southwestern Japan, during three dust storm events in spring 2000. The elemental composition and size of individual dust particles and their mixture state with sea salt, sulfate, and nitrate were analyzed using electron microscopes and an energy dispersive X-ray spectrometer. About 60 ∼ 85% of dust particles were internally mixed with sea salt. Weather records indicated these particles were most probably formed by the collisions and coagulations of dust particles and sea-salt particles. The relative weight ratios of mineral components to sea salt in individual particles showed that the mixtures of particles were dominated by mineral, by sea salt, or by both. Size distributions of the particles segregated by the mixture levels of mineral and sea salt in the three dust storm events were similar and all distributions showed a diameter range of 1 ∼ 8 μm with maximum mode around 3 μm. Out of 1 ∼ 8 μm, dust particles were rarely detected. The combination of dust particles with sea salt caused an increase in size of the dust particles. Therefore the decrease of particle concentrations in the range of diameter >3 μm suggests the critical diameter for dust particle dispersion was possibly around 3 μm and a dust particle might be removed rapidly if it became larger than this scale in the marine atmosphere. Detection of sulfate and nitrate revealed that 91% or more dust particles contained sulfate and 27% or less contained nitrate. The comparisons of the relative weight ratios of sodium, sulfur, and chlorine in mixture particles and in sea-salt particles confirmed previous results that mineral materials could enhance particulate sulfate and nitrate formation and restrain chlorine depletion from the sea-salt components in mixture particles.

Spatial and temporal variability in phytoplankton iron limitation along the California coast and consequences for Si, N, and C biogeochemistry

Abstract: [1] Iron limitation was investigated along the Northern California coast in the summer of 1999. Small-volume (1 l) shipboard iron addition bottle experiments were performed at 44 stations to gain the greatest possible temporal and spatial coverage of the area. Parameters measured in these 4-day incubations included size-fractionated chlorophyll a and particulate nutrients (C, N, and Si). Degrees of community iron limitation were quantified and compared using various iron limitation indexes, calculated as the ratio of chlorophyll a, particulate organic nitrogen, or particulate organic carbon produced in Fe-amended bottles to the amounts produced in controls. Iron limitation occurred most frequently and was most severe on stations off the continental shelf, away from sedimentary sources of iron, as well as during relaxation events in aged upwelled water. Size-fractionated chlorophyll a data did not suggest large Fe-mediated changes in phytoplankton community composition. Fe limitation reduced phytoplankton production of particulate organic nitrogen and carbon, but had much less effect on biogenic silica production. The result is an increase in particulate Si:N and Si:C ratios of control samples, which were frequently double those of Fe-amended samples. Particulate C:N ratios also decreased under Fe limitation, indicating that iron availability exerts a strong control on C, N, and Si elemental composition of phytoplankton, and thus on the biogeochemical cycling of these nutrients in the California upwelling region.

The 2001 Asian dust events: Transport and impact on surface aerosol concentrations in the U.S.

Abstract: A transport event in April 2001 brought substantial quantities of mineral dust from Asian deserts to the U.S. atmospheric boundary layer (ABL). The dust was seen in large amounts throughout the ABL in the U.S., with almost no reduction in concentrations. It was estimated that the amount of Asian dust in the continental U.S. ABL in mid-April 2001 was 1.1 E5 metric tons, a value comparable to the daily emission flux of all U.S. sources of particulate matter (PM) less then 10 μm diameter (PM 10). In some regions, the Asian dust, combined with local pollution, elevated urban PM to levels associated with adverse health effects. The April 2001 event appears to be the largest Asian dust event ever observed in the U.S., and its effects provide evidence that air pollution issues must be viewed in a global context.

Simultaneous Low Engine-Out NOx and Particulate Matter with Highly Diluted Diesel Combustion

Abstract: This paper describes the simultaneous reduction of nitrogen oxides (NOx) and particulate matter (PM) in a modern light-duty diesel engine under high exhaust gas recirculation (EGR) levels. Simultaneous reduction of NOx and PM emissions was observed under lean conditions at several low to moderate load conditions using two different approaches. The first approach utilizes a throttle to increase EGR rate beyond the maximum rate possible with sole use of the EGR valve for a particular engine condition. The second approach does not use a throttle, but rather uses a combination of EGR and manipulation of injection parameters. A significant reduction in particulate matter size and concentration was observed corresponding to the reduction in particulate mass. This PM reduction was accompanied by a significant shift in the heat release profile. In addition, there were significant cylinder-to-cylinder variations in particulate matter characteristics, gaseous emissions, and heat release. A fuel penalty is associated with operating in the low NOx and low PM regime when there are no modifications to the injection strategy. Preliminary experiments indicate that the penalty can be eliminated or reduced to a few percent while still maintaining a significant reduction in NOx and PM. An improved understanding of this combustion regime will lead to improved EGR utilization for lowering the performance requirements of post-combustion emissions controls.

Variability in ammonium nitrate formation and nitric acid depletion with altitude and location over California

Abstract: [1] Spatial variations in the partitioning of nitrate between gas phase nitric acid (HNO3) and particulate ammonium nitrate were observed using airborne measurements of trace gas mixing ratios, particle size distributions, and particle composition. During the Intercontinental Transport and Chemical Transformation experiment in April and May 2002 the NOAA WP-3 aircraft flew up to 8 km altitude on 11 research flights from Monterey, California. The formation of semivolatile aerosols was studied by examining the enhancement of fine-particulate ammonium nitrate and depletion of gas-phase HNO3 over the San Joaquin Valley, Los Angeles Basin, and Mojave Desert. Gas-phase particle precursors, HNO3 and ammonia (NH3), were converted to particulate ammonium nitrate at higher altitudes within the boundary layer. These particle layers were a consequence of lower ambient temperatures that caused a reduction of the dissociation constant for ammonium nitrate aerosol so that gas phase HNO3 was depleted and particle mass was formed. The resulting vertical gradients in particulate matter and HNO3 were observed in well-mixed boundary layers where other directly emitted trace gases (CO) and secondary pollutants (O3) exhibited no vertical gradients. Hence the equilibrium between the gas and particle phases occurred faster than boundary layer mixing times and chemical rather than meteorological effects were responsible for the layers of enhanced particulate matter aloft. Coincident HNO3 depletion and ammonium nitrate formation was also observed downwind from regions characterized by large agricultural NH3 emissions in the Los Angeles Basin and San Joaquin Valley.

Effects of changes in sulfate, ammonia, and nitric acid on particulate nitrate concentrations in the southeastern United States.

Abstract: A thermodynamic equilibrium model, Simulating Composition of Atmospheric Particles at Equilibrium (SCAPE2), was used to investigate the response of fine particulate NO3 − to changes in concentrations of HNO3 , NH3 , and SO4 2− in the southeastern United States. The data consisted of daily, 24-hr time resolution measurements from the Aerosol Research Inhalation Epidemiology Study (ARIES) Jefferson Street (Atlanta) site and five other sites of the Southeastern Aerosol Research and Characterization Project (SEARCH). Reductions of total NH3 (gas-phase NH3 plus particulate NH4 +), total NO3 − (HNO3 plus particulate NO3 −), SO4 2−, or combined total NO3 − (HNO3 plus particulate NO3 −) with SO4 2− were used to estimate the effects of changing emission levels. The conversion of SO2 to SO4 2− and NO2 to HNO3 involves additional nonlinear reactions not incorporated into the model. For all sites, fine particulate NO3 − concentrations decreased in response to reductions of either NH3 or total NO3 −, but the ...