Black Carbon Aerosol at McMurdo Station,Antarctica

ABSTRACT

Aerosol light absorption as black carbon (BC) was measured from November 19, 1995, to February 6, 1996, at a location 0.65 km downwind of the center of McMurdo Station on the Antarctic coast. The results show a bimo-dal frequency distribution of BC concentrations. Approximately 65% of the measurements were found in a mode at a low range of concentrations centered at ~20 ng/m³. These concentrations are higher than those found at other remote Antarctic locations and probably represent contamination from the station. The remaining measurements were in a high-concentration mode (BC ~300 ng/m³), indicating direct impact of local emissions from combustion activities at the station. High values of BC were associated with winds from the direction of the station, and the BC flux showed a clear directionality. Maximum BC concentrations occurred between 7:00 and 11:00 a.m. The "polluted" mode accounted for more than 80% of the BC frequency-weighted impact at this location.     

Light Scattering from Sea-Salt Aerosols at Interagency Monitoring of Protected Visual Environments (IMPROVE) Sites

Abstract

A method is described to estimate light scattering (Bsp) by sea-salt aerosols at coastal locations in the Interagency Monitoring of Protected Visual Environments (IMPROVE) network. Dry mass scattering efficiencies for fine and coarse sea-salt particles were based on previously measured dry sea-salt size distributions. Enhancement of sea-salt particle scattering by hygroscopic growth was based on NaCl water activity data. Sea-salt aerosol mass at the IMPROVE site in the Virgin Islands (VIIS) was estimated from strontium (Sr) concentrations in IMPROVE aerosol samples. Estimated Bsp, including contributions from sea-salt mass based on Sr, agreed well with measured Bsp at the VIIS IMPROVE site. On average, sea salt accounted for 52% of estimated Bsp at this site. Sea-salt aerosol mass cannot be reliably estimated from Sr unless its crustal enrichment factor exceeds 10. Sodium (Na) concentrations are not accurately determined by X-ray fluorescence analysis in IMPROVE samples. It is recommended that Na be measured in the fine and coarse modes by a more appropriate method, such as atomic absorption spectroscopy or ion chromatography, to account for scattering by sea-salt particles at IMPROVE sites where such contributions may be significant.     

PM2.5 source apportionment with organic markers in the Southeastern Aerosol Research and Characterization (SEARCH) study

Positive matrix factorization (PMF) and effective variance (EV) solutions to the chemical mass balance (CMB) were applied to PM_2.5 (particulate matter with an aerodynamic diameter <2.5 μm) mass and chemically speciated measurements for samples taken from 2008 to 2010 at the Atlanta, Georgia, and Birmingham, Alabama, sites. Commonly measured PM_2.5 mass, elemental, ionic, and thermal carbon fraction concentrations were supplemented with detailed nonpolar organic speciation by thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS). Source contribution estimates were calculated for motor vehicle exhaust, biomass burning, cooking, coal-fired power plants, road dust, vegetative detritus, and secondary sulfates and nitrates for Atlanta. Similar sources were found for Birmingham, with the addition of an industrial source and the separation of biomass burning into open burning and residential wood combustion. EV-CMB results based on conventional species were qualitatively similar to those estimated by PMF-CMB. Secondary ammonium sulfate was the largest contributor, accounting for 27–38% of PM_2.5, followed by biomass burning (21–24%) and motor vehicle exhaust (9–24%) at both sites, with 4–6% of PM_2.5 attributed to coal-fired power plants by EV-CMB. Including organic compounds in the EV-CMB reduced the motor vehicle exhaust and biomass burning contributions at both sites, with a 13–23% deficit for PM_2.5 mass. The PMF-CMB solution showed mixing of sources within the derived factors, both with and without the addition of speciated organics, as is often the case with complex source mixtures such as those at these urban-scale sites. The nonpolar TD-GC/MS compounds can be obtained from existing filter samples and are a useful complement to the elements, ions, and carbon fractions. However, they should be supplemented with other methods, such as TD-GC/MS on derivitized samples, to obtain a wider range of polar compounds such as sterols, sugars, and organic acids. The PMF and EV solutions to the CMB equations are complementary to, rather than replacements for, each other, as comparisons of their results reveal uncertainties that are not otherwise evident.

Implications:?Organic markers can be measured on currently acquired PM_2.5 filter samples by thermal methods. These markers can complement element, ion, and carbon fraction measurements from long-term speciation networks. Applying the positive matrix factorization and effective variance solutions for the chemical mass balance equations provides useful information on the accuracy of the source contribution estimates. Nonpolar compounds need to be complemented with polar compounds to better apportion cooking and secondary organic aerosol contributors.     

Hygroscopic organic aerosols during BRAVO?

The hygroscopic properties of the organic fraction of aerosols are poorly understood. The ability of organic aerosols to absorb water as a function of relative humidity (RH) was examined using data collected during the 1999 Big Bend Regional Aerosol and Visibility Observational Study (BRAVO). (On average, organics accounted for 22% of fine particulate matter with an aerodynamic diameter less than 2.5 microm (PM2.5) mass). Hourly RH exceeded 80% only 3.5% of the time and averaged 44%. BRAVO aerosol chemical composition and dry particle size distributions were used to estimate PM2.5 light scattering (Bsp) at low and high ambient RH. Liquid water growth associated with inorganic species was sufficient to account for measured Bsp for RH between 70 and 95%.     

Comparison of particle light scattering and fine particulate matter mass in central California

Particle light scattering (Bsp) from nephelometers and fine particulate matter (PM2.5) mass determined by filter samplers are compared for summer and winter at 35 locations in and around California's San Joaquin Valley from December 2, 1999 to February 3, 2001. The relationship is described using particle mass scattering efficiency (sigmasp) derived from linear regression of Bsp on PM2.5 that can be applied to estimated PM2.5 from nephelometer data within the 24-hr filter sampling periods and between the every-6th-day sampling frequency. An average of sigmaSp = 4.9 m2/g was found for all of the sites and seasons; however, sigmasp averaged by site type and season provided better PM2.5 estimates. On average, the sigmasp was lower in summer than winter, consistent with lower relative humidities, lower fractions of hygroscopic ammonium nitrate, and higher contributions from fugitive dust. Winter average sigmasp were similar at non-source-dominated sites, ranging from 4.8 m2/g to 5.9 m2/g. The sigmasp was 2.3 m2/g at the roadside, 3.7 m2/g at a dairy farm, and 4.1 m2/g in the Kern County oilfields. Comparison of Bsp from nephelometers with and without a PM2.5 inlet at the Fresno Supersite showed that coarse particles contributed minor amounts to light scattering. This was confirmed by poorer correlations between Bsp and coarse particulate matter measured during a fall sampling period.     

Sources of PM10 and sulfate aerosol at McMurdo Station, Antarctica

Source contributions to PM10 and sulfate aerosol at McMurdo Station, Antarctica during the austral summers of 1995-1996 and 1996-1997 were estimated using Chemical Mass Balance (CMB) receptor modeling. The average PM10 (particles with aerodynamic diameters less than 10 microm) concentration at Hut Point, located less than 1 km downwind of downtown McMurdo, was 3.4 microg/m3. Emissions profiles were determined for potentially important aerosol source types in McMurdo: exposed soil, power generation, space heating, and surface vehicles. Soil dust, sea salt, combustion emissions, sulfates, marine biogenic emissions as methanesulfonate, and nitrates contributed 57%, 15%, 14%, 10%, 3%, and 1%, respectively, of average estimated PM10 at Hut Point (3.2 microg/m3). Soil dust, sea salt, and combustion sources contributed 12%, 8%, and 20%, respectively, of the average PM10 sulfate concentration of 0.46 microg/m3. Marine biogenic sources contributed 0.17 microg/m3 (37%). The remaining sulfate is thought to have come from emissions from Mt. Erebus or hemispheric pollution sources.     

Evaluation of the IMPROVE Equation for estimating aerosol light extinction

The [revised] IMPROVE Equation for estimating light extinction from aerosol chemical composition was evaluated considering new measurements at U.S. national parks. Compared with light scattering (Bsp) measured at seven IMPROVE sites with nephelometer data from 2003–2012, the [revised] IMPROVE Equation over- and underestimated Bsp in the lower and upper quintiles, respectively, of measured Bsp. Underestimation of the worst visibility cases (upper quintile) was reduced by assuming an organic mass (OM)/organic carbon (OC) ratio of 2.1 and hygroscopic growth of OM, based on results from previous field studies. This assumption, however, tended to overestimate low Bsp even more. Assuming that sulfate was present as ammonium bisulfate rather than as ammonium sulfate uniformly reduced estimated Bsp. The split-mode model of concentration- and size-dependent dry mass scattering efficiencies in the [revised] IMPROVE Equation does not eliminate systematic biases in estimated Bsp. While the new measurements of OM/OC and OM hygroscopicity should be incorporated into future iterations of the IMPROVE Equation, the problem is not well constrained due to a lack of routine measurements of sulfate neutralization and the water-soluble fraction of OM in the IMPROVE network.

Implications: Studies in U.S. national parks showed that aerosol organics contain more mass and absorb more water as a function of relative humidity than is currently assumed by the IMPROVE Equation for calculating chemical light extinction. Consideration of these results could significantly shift the apportionment of light extinction to water-soluble organic aerosols and therefore better inform pollution control strategies under the U.S. Environmental Protection Agency Regional Haze Rule.     

Air Quality Measurements from the Fresno Supersite

ABSTRACT

The Fresno Supersite intends to 1) evaluate non-routine monitoring methods, establishing their comparability with existing methods and their applicability to air quality planning, exposure assessment, and health effects studies; 2) provide a better understanding of aerosol characteristics, behavior, and sources to assist regulatory agencies in developing standards and strategies that protect public health; and 3) support studies that evaluate relationships between aerosol properties, co-factors, and observed health end-points. Supersite observables include in-situ, continuous, short-duration measurements of 1) PM_2.5, PM₁₀, and coarse (PM₁₀ minus PM_2.5) mass; 2) PM_2.5 SO₄ ^-2, NO₃ ^-, carbon, light absorption, and light extinction; 3) numbers of particles in discrete size bins ranging from 0.01 to ~10μm; 4) criteria pollutant gases (O₃, CO, NO_x); 5) reactive gases (NO₂, NO_y, HNO₃, peroxyacetyl nitrate [PAN], NH₃); and 6) single particle characterization by time-of-flight mass spectrometry. Field sampling and laboratory analysis are applied for gaseous and particulate organic compounds (light hydrocarbons, heavy hydrocarbons, carbonyls, polycyclic aromatic hydrocarbons [PAH], and other semi-volatiles), and PM_2.5 mass, elements, ions, and carbon. Observables common to other Supersites are 1) daily PM_2.5 24-hr average mass with Federal Reference Method (FRM) samplers; 2) continuous hourly and 5-min average PM_2.5 and PM₁₀ mass with beta attenuation monitors (BAM) and tapered element oscillating microbalances (TEOM); 3) PM_2.5 chemical specia-tion with a U.S. Environmental Protection Agency (EPA) speciation monitor and protocol; 4) coarse particle mass by dichotomous sampler and difference between PM₁₀ and PM_2.5 BAM and TEOM measurements; 5) coarse particle chemical composition; and 6) high sensitivity and time resolution scalar and vector wind speed, wind direction, temperature, relative humidity, barometric pressure, and solar radiation. The Fresno Supersite is coordinated with health and toxicological studies that will use these data in establishing relationships with asthma, other respiratory disease, and cardiovascular changes in human and animal subjects.     

Environmental perception: An odyssey of ideas

Convergent interests paved the way for multidisciplinary research in environmental perception and behavior, in which the Clark Group was an important focus. For me that fruitful conjunction began in the mid-1960s, when I taught at Clark and had just embarked on a large-scale assessment of observer responses to urban milieus. Through the early 1970s the Clark Group helped to catalyze perception insights generally and to guide my own work. Emigration to Britain in 1972 distanced me from that ambience and style of inquiry, but the Clark experience continues to inform by perceptual excursions into images of the past.Specific memories of Clark merge with general judgements about the fortunes of environmental perception research. By the early 1970s it was already clear that various drains on scanty human resources in this new field left insufficient concerted attention for theory and synthesis. The 15 years since have seen little fundamental progress. Much research seems narrow in scope, lifeless in tone, and trivial in its conclusions. Exciting advances can be found along a number of peripheries, but the centre seems devoid of spirit.