Robert A. Gorse

The contribution of elemental carbon to the optical properties of rural atmospheric aerosols

Measurements of carbonaceous aerosol, aerosol light absorption and aerosol light scattering were made at two rural sites in southwestern Pennsylvania during August 1983. Aerosol light absorption ranged from 5.2 × 10−6 m−1 to 6.4 × 10−5 m−1 (average: 1.9 × 10−5 m−1) and accounted for about 13% of the aerosol total light extinction. Elemental carbon, averaging 1.3 μg m−3 at the two sites (and comprising some 36 % of the aerosol carbon), accounted for effectively all (> 95 %) of the aerosol light absorption.

Comparison of Solvent Extraction and Thermal-Optical Carbon Analysis Methods: Application to Diesel Vehicle Exhaust Aerosol

Filter samples of particulate emissions from two diesel automobiles were analyzed by solvent extraction with a hot toluene/1-propanol mixture, by thermal-optical carbon analysis, and by X-ray fluorescence analysis. On the average, carbon accounted for 83% of the particulate matter, and organic carbon comprised 70% of the extractable mass. The ratio of elemental carbon as measured by the thermal-optical technique to unextractable mass was 1.05 +/- 0.04. For most of the filters the unextractable mass was predominantly elemental carbon. However, for the filters with the largest amounts of unextracted material the elements Fe, S, Al, Si, and Ca were present in significant amounts (0.3-5% each of the unextractable mass when expressed as oxides). 29 references.

Atmospheric acidity measurements on allegheny mountain and the origins of ambient acidity in the Northeastern United States

Abstract Atmospheric acidity as HNO3(g), SO2(g), and aerosol H+ was measured on Allegheny Mountain and Laurel Hill in southwest Pennsylvania in August 1983. The aerosol H+ appeared to represent the net after H2SO4 reaction with NH3(g). The resulting H + SO 4 2− ratio depended on SO42− concentration, approaching that of H2SO4 at the highest SO42− concentrations. The atmosphere was acidic; the average concentrations of HNO3 (78 nmole m−3) and aerosol H+ (205 nmole m−3), NH4+ (172 nmole m−3) and SO42− (201 nmole m−3), and the dearth of NH3(〈 15 nmolem−3), show that the proton acidity (HNO3, H2SO4) of the air exceeded the acid-neutralizing capacity of the air by a factor of > 2, with one 10-h period averaging 263 and 844 nmolem−3 for HNO3 and aerosol H+, respectively. SO2 added another 900 nmole m−3 (average) of potential H+ acidity. HNO3 and aerosol H+ episodes were concurrent, on 7–8 day cycles, unrelated to SO2 which existed more in short-lived bursts of apparently more local origin. NOx was sporadic like SO2. Laurel and Allegheny, separated by 35.5 km, were essentially identical in aerosol SO42−, and in aerosol H+, less so in HNO3 and especially less so in SO2; apparently, chemistry involving HNO3 and aerosol H+ or SO42− was slow compared to inter-site transport times (1–2 h). From growth of bscat and decline of SO2 during one instance of inter-site transport, daytime rate coefficients for SO2 oxidation and SO2 dry deposition were inferred to have been, respectively, ~ 0.05 and ⩽ 0.1 h−1. HNO3 declined at night. Aerosol H+ and SO42− showed no significant diurnal variation, and O3 showed very little; these observations, together with high PAN NO x ratios, indicate that regional transport rather than local chemistry is governing. The O3 concentration (average 56 ppb or 2178 nmolem−3) connotes an oxidizing atmosphere conducive to acid formation. Highest atmospheric acidity was associated with (1) slow westerly winds traversing westward SO2 source areas, (2) local stagnation, or (3) regional transport around to the back side of a high pressure system. Low acidity was associated with fast-moving air masses and with winds from the northerly directions; upwind precipitation also played a moderating role in air parcel acidity. Much of the SO2 and NOx, and ultimately of the HNO3 and aerosol H+, appeared to originate from coal-fired power plants. An automotive contribution to the NOx and HNO3 could not be discerned. Size distributions of aerosol H+ and SO42− were alike, with MMED ~ 0.7 μm, in the optimum range for efficient light scattering and inefficient wet/dry removal. Thus, light scattering and visual range degradation were attributable to the acidic SO42− aerosol, linking the issues of acid deposition and visual air quality in the Northeast. With inefficient removal of aerosol H+, and inefficient night-time removal of HNO3, strong acids may be capable of long-distance transport in the lower troposphere. We obtained an accounting of aerosol mass in terms of composition, including aerosol H2O which was shown to account for much of the light scattering.

Mutagenicity and chemical characteristics of carbonaceous particulate matter from vehicles on the road.

Experiments were conducted in the Allegheny Mountain Tunnel of the Pennsylvania Turnpike in 1979 to evaluate bacterial mutagenicities of particulate emissions from heavy-duty diesels and gasoline-powered vehicles in highway operation. Filter samples were extracted with dichloromethane followed by acetonitrile. Ames assays with and without microsomal activation, HPLC fluorescence profiles, GC molecular weight distributions, and particle size distributions were obtained. We find that (1) the diesel particulate matter at Allegheny resembles that encountered in dilution-tube studies by all criteria studied (particulate mass emission rate, extractability, particle size, extract HPLC profile, extract molecular weight distribution, and mutagenicity--though these findings do not preclude the possibility of substantial differences in detailed chemical properties), (2) in revertants per microgram of dichloromethane-extracted material at Allegheny, the mutagenicities of the diesel particulate matter and of the local rural ambient particulate matter are of the same order of magnitude, and (3) in revertants per kilometer traveled, the mutagenicity of particulate emissions from heavy-duty diesels is several times (median approx.6 times) that of emissions from gasoline-powered vehicles.

1-Nitropyrene concentration and bacterial mutagenicity in on-road vehicle particulate emissions

1-Nitropyrene (1NP) has been detected in the particulate emissions from on-road vehicles during an experiment conducted at the Allegheny Mountain Tunnel on the Pennsylvania Turnpike. 1NP emission rates and mutagenicities (Ames activities) of the emissions were determined for heavy-duty diesel trucks and for light-duty spark-ignition vehicles. The 1NP concentrations in the particulate extracts and also the 1NP emission rates are lower than would be predicted on the basis of laboratory dilution tunnel measurements either for diesels or for spark-ignition vehicles. 1NP accounts for very little of the on-road mutagenicity - indicating that other, unidentified, direct-acting mutagens are responsible for on-road vehicular exhaust mutagenicities. Recovery of 1NP from diesel particulate material appears to be independent of 1NP concentration and filter storage time at -80/sup 0/C prior to extraction.

Development of a Desulfurization Strategy for a NOx Adsorber Catalyst System

Improve NOx regeneration calibration developed in DECSE Phase I project to understand full potential of NOx adsorber catalyst over a range of operating temperatures. Develop and demonstrate a desulfurization process to restore NOx conversion efficiency lost to sulfur contamination. Investigate effect of desulfurization process on long-term performance of the NOx adsorber catalyst.

Impact of methanol vehicles on ozone air quality

Abstract A single-cell trajectory model with an updated chemical mechanism has been used to evaluate the impact on ozone air quality of methanol fueled vehicle (MFV) substitution for conventional fueled vehicles (CFV) in 20 urban areas in the U.S. Recent measurement data for non-methane organic compound (NMOC) concentrations and NMOC NO x ratios for each of the areas was used. The sensitivity of peak 1-h O3 values to variations in many of the input parameters has been tested. The functional dependence of peak 1-h O3 on NMOC NO x , ratios shows that, for many cities, the maximum O3 levels occur near the median urban-center 6–9 a.m. NMOC NO x ratios. The results of the photochemical model computations, including several methanol-fuel substitution scenarios, have been used to derive relative reactivities of methanol and formaldehyde. Per-vehicle O3 reduction potentials for MFV have also been derived. The reduction potentials and calculated percentage O3 reductions for selected MFV market-penetrations have been used to estimate the impact of any MFV market-penetration or change in MFV emission factors. All substitution scenarios evaluated lead to projections of lower peak 1-h O3 levels. Even with significant replacement of CFV by MFV, the reduction of urban O3 levels appears to be modest. However, the reductions may be significant in comparison to other available O3-reduction options.

The sources of aerosol elemental carbon at Allegheny Mountain

Abstract Aerosol elemental carbon measurements were taken at two rural sites in southwestern Pennsylvania during August 1983. Carbon, though a small part of the aerosol mass at both sites, was a leading constituent of the aerosol on an atom basis. Time-weighted average concentrations at Allegheny Mountain and Laurel Hill were 1.2 and 1.4 μg m −3 , respectively. Absolute Principal Component Analysis followed by multiple regression and Chemical Mass Balance techniques were utilized to apportion the measured elemental carbon to its sources. Motor vehicles were estimated to be the largest source of elemental carbon at the two sites, contributing 41–68% and 34–56% at Allegheny Mountain and Laurel Hill, respectively.

Real-world vehicle emissions: a summary of the third annual CRC-APRAC on-road vehicle emissions workshop

The CRC-APRAC On-Road Vehicle Emissions Workshop provided an informal atmosphere for the exchange of information on real-world vehicle emissions issues. Topics addressed included: emissions inventories; mobile source emission factor models; evaporative emissions; dynamometer studies of exhaust emissions; remote sensing studies; and tunnel studies of vehicle emissions. It is now widely accepted that emissions inventories have significantly underestimated the carbon monoxide (CO) and hydrocarbon (HC) emissions from on-rpad vehicles. Since these inventories are used to develop emission control strategies, it is critical that they accurately reflect on-road emissions. Research is currently being conducted by a variety of organizations to address this issue. For the past three years, the Coordinating Research Council - Air Pollution Research Advisory Committee (CRC-APRAC) has sponsored an onroad vehicle emissions workshop whose purpose is to provide an informal forum in which recent real-world vehicle emission...

Effect of ambient humidity on dichotomous sampler coarse/fine ratios

Abstract Atmospheric aerosols were measured in August 1983 on Allegheny Mountain and Laurel Hill in southwestern Pennsylvania. Ambient humidity was observed to influence the coarse to fine particle ratios as determined by dichotomous samplers. This influence is evident in the particle mass and in its component chemical species. The sampling run with the most pronounced mass shift resulted in an apparent loss of 50 % of the fine mass and 66 % of the fine particle sulfur to the coarse fraction. The magnitude of the mass shift appears to be related to the length of time that the aerosol was in a saturated environment and also to the original dry particle size. These observations have serious implications for receptor modeling with dichotomous sampler data whenever only the fine particles are considered.