Wanda W. Brachaczek

Particulate Matter Associated with Vehicles on the Road

Experiments at the Allegheny and Tuscarora Mountain Tunnels of the Pennsylvania Turnpike in 1975–1979 have resulted in a comprehensive description of the airborne particulate matter associated with highway traffic. Because of strong variations of traffic composition with time, emission rates of most species were resolvable into emission rates for each of the two vehicle categories: gasoline-powered vehicles and heavy-duty diesels. Thirty-four elements were identified, accounting for all of the vehicle-derived airborne particulate mass. The principal component was carbon (elemental and organic) from exhausts of heavy-duty diesels, which comprised on the average 10%–15% of the traffic. Per vehicle-kilometer, diesels were the preponderant source of most of the other species as well. Other emissions resulted from oxidation of diesel-fuel sulfur to H2SO4 (5% of the particulate mass total for traffic overall), inorganic additives and adventitious components of fuels and motor oils (10% of the overall mass total...

The nitric acid shootout: field comparison of measurement methods

Eighteen instruments for measuring atmospheric concentrations of nitric acid were compared in an eight day field study at Pomona College, situated in the eastern portion of the Los Angeles Basin, in September 1985. The study design included collocated and separated duplicate samplers, and the analysis by each laboratory of a set of quality assurance filters, so that the experimental variability could be distinguished from differences due to measurement methods. For all sampling periods, the values for nitric acid concentrations reported by the different instruments vary by as much as a factor of four. The differences among measurement techniques increase with nitric acid loading, corresponding to a coefficient of variation of 40%. In contrast, samplers of the same design operated by the same group show variability of 11–27 %. Overall, the highest reported concentrations are observed with the filter packs and lower concentrations are observed by the annular denuders and tunable diode laser absorption spectrometers. When the nitric acid concentrations are high enough to be detected by the FTIR, the FTIR values are close to those obtained by the denuder difference method and to the mean value from the other sampler groups. In the absence of a reference standard for the entire study, measurement methods are compared to the average of four denuder difference method samplers (DDM). Filter pack samplers are higher than the DDM for both daytime and night-time sampling. Two different filter packs using Teflon® prefilters are higher than the DDM by factors of 1.25 and 1.4. The results from the three annular denuders do not agree; the ratios of means to the DDM value are 1.0,0.8 and 0.6. For the transition flow reactor method and for two dichotomous samplers operated as denuder difference samplers, the ratio of means to the DDM are 1.09 and 0.93, respectively. The tunable diode laser absorption spectrometers gave lower daytime and higher night-time readings compared to the DDM, especially during the last three days of the study. Averaged over the entire measurement period, the daytime ratio of TDLAS to DDM is 0.8 and the night-time ratio is 1.7.

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.

AMBIENT SULFATE MEASUREMENTS ON ALLEGHENY MOUNTAIN AND THE QUESTION OF ATMOSPHERIC SULFATE IN THE NORTHEASTERN UNITED STATES

An experimental study is described in which atmospheric aerosol measurements at Allegheny Mountain in southwestern Pennsylvania were used to search for interrelationships of SO/sub 4/(-), percentage SO/sub 2/-SO/sub 4/(-) conversion, meteorological properties, rainfall, visibility, light scattering, SO/sub 2/, aerosol mass, H(+), NO/sub 3/, various trace elements, and rainfall H(+) and SO/sub 4/(-). The selected woodland location is in the area of maximum SO/sub 4/(-) concentration in the northestern U.S. The results obtained show that aerosol H(+) and SO/sub 4/(-) were uniquely correlated with each other and with light scattering, that the light scattering was entirely attributable to SO/sub 4/(-), and that SO/sub 2/ is evidently not related to any other parameter. It is concluded that the SO/sub 4/(-) at Allegheny Mountain stemmed from transport, with or without SO/sub 2/ oxidation, from westward nonurban sources of some kind that were sources of very little else in the aerosol.

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.

Artifact Formation of Sulfate, Nitrate, and Hydrogen Ion on Backup Filters: Allegheny Mountain Experiment

Artifact sulfate formation in ambient conditions on filters of several types was evaluated by comparison between upstream and downstream tandem filters and also by comparison between filters operated in parallel. Some evaluation of artifact H+ and NO3 − was also performed. The experimental site was a tower on the top of Allegheny Mountain in southwestern Pennsylvania. Artifact SO4 = on backup filters was observed to be directly related to filter alkalinity, relative humidity, and cumulative exposure to SO2 with the more alkaline types converting ≥ 10% of the SO2 to which they were exposed, even after very long exposure. On the quartz-fiber backup filters, which gave relatively little artifact, the artifact SO4 = and NO3 − precursors seem to have the same origin as the atmospheric SO2. Artifact H+ was also related to atmospheric SO2, though not clearly to artifact SO4 =; on a mole basis, H+ was a leading, if not the major, artifact species on quartz-fiber backup filters. However, the backup filter method g...

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.

Coarse- and fine-particle atmospheric nitrate and HNO3(g) in Claremont, California, during the 1985 nitrogen species methods comparison study

Abstract Coarse (⩾ 1.5 μm) and fine (⩾ 1.5 μm) atmospheric particle nitrate were measured along with HNO3 (g) in 40 consecutive periods over the 8 days of the 1985 Nitrogen Species Methods Comparison Study in Claremont, California, in September 1985. HNO3(g)and fine-particle nitrate both showed pronounced (~ 10-fold) diurnal variations, with a mid-morning peak in the case of fine-particle nitrate and a mid-afternoon peak in the case of HNO3 (g). Coarse-particle nitrate showed relatively little diurnal variation. Time-average values over the whole experiment for HNO3(g), fine nitrate, and coarse nitrate were, respectively, 114, 128 and 114 nanomole m−3.

Sulfate Emissions from Catalyst-Equipped Automobiles on the Highway

The essential effect of the present results is to reinforce substantially the conclusions drawn earlier. H/sub 2/SO/sub 4/ from catalyst-equipped 49-state cars on the highway has still not developed into a serious problem, as of 1977, after 3 model-years of production. Sulfate concentrations in the tunnel are not greatly higher than ambient levels in spite of the lack of opportunity for atmospheric dispersion of the emissions. And even so, approx. 2/3 of the vehicle-generated SO/sub 4//sup -2/ in the tunnel still comes from the Diesel trucks, whose SO/sub 4//sup -2/ emission rates are considerable. Diesel cars may eventually appear in substantial numbers; their SO/sub 4//sup -2/ emission rates are currently approx. 10 mg/km, comparable to a catalyst-equipped gasoline powered car or approx. 1/3 that of a heavy-duty Diesel. It should be emphasized that the present results and conclusions would not necessarily apply in California (where different emission control technology exists) or in future years even at the present site (as emission standards and control systems continue to change).

Dew Chemistry and Acid Deposition in Glendora, California, During the 1986 Carbonaceous Species Methods Comparison Study

Dew was collected and analyzed during the Carbonaceous Species Methods Comparison Study in the Los Angeles basin (Glendora, CA) in August 1986. Formate, acetate, and other carboxylate anions were consistently observed, with formate generally being the most abundant anion in the dew. These carboxylate anions appear to be attributable to deposition of carboxylic acids from the ambient air. Free acid (H+) was only about one-fifth of the total dew acidity; carboxylic acids could have accounted for half of the remainder. The H+ concentrations were far lower than in dew in the northeast United States (respective pH averages 4.7 and 4.0). Whereas dew in the Northeast was essentially a dilute HNO3/ H2SO4 mixture, that in Glendora contained substantial amounts of many other inorganic species. S(IV) in the dew in Glendora was stable against oxidation, even by H2O2, probably signifying formation of the bisulfite adduct with formaldehyde (considerable amounts of formaldehyde and acetaldehyde were present), in contras...