Road dust

Isotopic and chemical patterns are given for an ambient sample (downtown Portland) and four sources of carbonaceous particles. The source C contributions (Ct) are expressed as percent of total aerosol mass, and the subscripts refer to Vegetation (slash burning), Road dust, Oil (residual and distillate), and Auto exhaust. Units for the ordinate are also percent of total aerosol mass, except for, 4C which is expressed as dpm/g-aerosol. Abscissa points for each pattern are ordered as l4C, C, Si, Ni, and Pb. 

Soil resuspension has the capability of entraining significant volumes of Pb into the air of urban areas. Harris Davidson (2005) calculated that resuspension of soil is responsible for generating 54,000 kg of airborne Pb each year in the South Coast Air Basin of California (SOCAB) and will remain a major source well into the future. Similarly, Lankey et al. (1998) concluded that 43% of Pb emissions in the South Coast Air Basin in California resulted from the resuspension of soil and road dust. 

City and season Diesel Gasoline Road dust Coal Biomass Secondary sulfates Secondary nitrates Secondary ammonium Total... 

Vasiloff, G. N., and D. B. Drummond. The effectiveness of road dust as a protective agent on buckwheat and pinto bean against sulfur dioxide and ozone. Phytopathology 64 588, 1974. (abstract)... 

With emission source chemical signatures and corresponding aerosol or rainwater sample measurements PLS can be used Co calculate a chemical element mass balance (CEB). Exact emission profiles for the copper smelter and for a power plant located further upwind were not available for calculation of source contributions to Western Washington rainwater composition. This type of calculation Is more difficult for rainwater Chan for aerosol samples due Co atmospheric gas to particle conversion of sulfur and nitrogen species and due Co variations In scavenging efficiencies among species. Gatz (14) has applied Che CEB to rainwater samples and discussed Che effect of variable solubility on the evaluation of Che soil or road dust factor. 

In urban areas, the typical dominant sources of fine organic aerosol particles are diesel exhaust, gasoline-powered vehicle exhaust, meat cooking operations, smoke from wood combustion, and paved road dust followed by four smaller sources of particles tire wear, vegetative detritus, natural gas combustion, and cigarette smoke. ... 

Unpaved road dust or aerosols contributes to haze in class I airsheds. 

Uses of calcium chloride include road deicing (40%), where it competes with sodium chloride, road dust control and roadway base stabilization (20%), industrial processing (20%), oil and gas wells (10%), and concrete... 

Calcium chloride has several industrial applications. The major applications of this compound are in deicing of roads, dust control, imparting stability to roads and buildings, and to improve traction in tractor tires. It is mixed with ice to make freezing mixtures. Hexahydrate mixed with crushed ice can lower the temperature of the cooling bath to below -50°C. It also is used as a desiccant for dehydrating gases and liquids. It is added to cement in various proportions to manufacture different types of concrete. Other uses are in adhesives, to lower gel temperatures, and as a calcium source in liquid feed supplements for dairy cattle. Also, the compound is used to control particle size development and reduce coalescence in plastics. 

This particle sorting removes chemical interferences and Increases analytical sensitivity. It also Increases the level of confidence when most of a road dust contribution is, for example, found in the coarse fraction. 

A major limitation of receptor models is their inability to distinguish between specific sources within a source type. Resuspended road dust may be a major cause of standard violations, but until the offending roadways can be pinpointed, a control strategy cannot be implemented. A major limitation of source models is the necessity to estimate emission rates from the many, diverse producers of suspended particulate matter. The receptor model quantifies the source type contributions. Only the major contributors need to be evaluated for the source model, so that resources which might have been used to inventory... 

Soil and road dust was found to be the largest single source, accounting for 55% of the particulate. Although several minor sources of rural dust were included in the area s inventory, the study identified a 19,400 ton per year deficiency in the paved road dust emission inventory. 

Three source classes were selected for comparison of CMB and model results. Two were of an area source nature (road dust and automotive exhaust) and one point source category (residual oil combustion). These sources were selected for comparison for the following reasons ... 

Dust from paved and unpaved roads is the most predominant source in Portland. Accurate emissions data is critical to the model s ability to account for all of the measured mass, as well as to the development of a successful strategy. Although the CMB model cannot distinguish between dust emissions from paved and unpaved roads, it can typically assign total dust impacts to within a 5-6% uncertainty. Leaded automotive tailpipe exhaust was selected because it can be accurately estimated by CMB and is the third most abundant contributor to the annual particulate mass, after road dust and vegetative burning. 

Road dust comparisons shown in Figure 4 were poor with major underpredletions at all locations by the GRID model. More work was obviously needed before it could realistically predict dust impacts. 

Figure 4. Road dust impacts—north wind regime (initial predictions)...

Road dust underpredictions, based on the initial EPA generalized paved road dust factor, were the most serious problem. Since there are very few unpaved roads within the AQMA, attention turned to upward adjustment of the paved road dust emission factor. 

A modified emission factor (EE) was developed based on an assumed consistent relationship between particulate tailpipe and road dust impact ... 

Values To Meet Secondary Road Dust Auto Wood All Point... 

Road dust emission inventory errors were corrected after comparing dispersion model and CMB results. Road dust emissions were increased by 2300 tons in Medford as a result of emission factor adjustments and changes in the unpaved road dust inventory. 

In Eugene, new measurements of traffic volume and vehicle speeds on unpaved roads led to a 2600 ton per year reduction in road dust emissions. 

Major changes in the Medford model s treatment of area source impacts were completed after early results consistently underpredicted road dust impacts measured by CMB. As a result, model performance improved dramatically. 

In a search for sources of alkaline materials in rural air and rain, we have sampled and performed multi-element analyses on ambient particulate matter and potential source materials. Ambient aerosols were sampled daily using single Nuclepore filters or Florida State University "streakers." Samples of soil and unpaved road materials were also collected and analyzed. The samples were analyzed by various multi-element methods, including ion-and proton-induced X-ray emission and X-ray fluorescence, as well as by atomic absorption spectrophotometry. Visual observations, as well as airborne elemental concentration distributions with wind direction and elemental abundances in aerosols and source materials, suggested that soil and road dust both contribute to airborne Ca. Factor analysis was able to identify only a "crustal" source, but a simple mass balance suggested that roads are the major source of Ca in rural central Illinois in summer. 

Source Materials. Two categories of local source materials were sampled - road dust and soil. Samples of bulk soil were removed from the upper 10 cm of the soil column at 74 locations over portions of the 1 km centered on the ground site. A square grid spacing of 160 m (0.10 mi) between sampling locations was used. Before analysis, the samples were air dried, crushed, and sieved to remove the larger particles (>53 pm diameter) which would not be likely to be raised by the wind. 

Analysis of both soil and road dust for Al, Si, K, Ti, and Fe was performed at the Illinois State Geological Survey, using X-ray fluorescence techniques (O. Ca and K were determined at the Water Survey by atomic absorption spectrophotometry (AAS) following LIBO3 fusion to disolve the sample ). 

Table I. Mean abundances of crustal elements in aerosols, soil, and road dust in a rural area near Champaign, IL.

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