Douglas S. Shadwick

Spatial Variability of PM2.5 in Urban Areas in the United States

Abstract Data from the U.S. Environmental Protection Agencys Aerometric Information Retrieval System (now known as the Air Quality System) database for 1999 and 2000 have been used to characterize the spatial variability of concentrations of particulate matter with aerodynamic diameter ≤2.5 μg (PM2.5) in 27 urban areas across the United States. Different measures were used to quantify the degree of uniformity of PM2.5 concentrations in the urban areas characterized. It was observed that PM2.5 concentrations varied to differing degrees in the urban areas examined. Analyses of several urban areas in the Southeast indicated high correlations between site pairs and spatial uniformity in concentration fields. Considerable spatial variation was found in other regions, especially in the West. Even within urban areas in which all site pairs were highly correlated, a variable degree of heterogeneity in PM2.5 concentrations was found. Thus, even though concentrations at pairs of sites were highly correlated, their concentrations were not necessarily the same. These findings indicate that the potential for exposure misclassification errors in time-series epidemiologic studies exists.

An environmental scoping study in the Lower Rio Grande Valley of Texas — III. Residential microenvironmental monitoring for air, house dust, and soil

A principal aspect of the 1993 Lower Rio Grande Valley Environmental Scoping Study was the analysis and interpretation of residential air, household dust, and soil pollutant concentration data for exposure assessments. Measurements included respirable particulate matter (PM2.5), volatile organic compounds (VOCs), pesticides, and polycyclic aromatic hydrocarbons (PAHs) in indoor and outdoor air. Household dust, road dust, and yard soil were analyzed for elements, pesticides, and PAHs. Nine residences were monitored for three weeks in the spring of 1993. Additional monitoring was conducted at six of the nine residences for ten days the following summer. Generally good agreement was found between outdoor residential air and same-species measurements collected concurrently at a non-residential central site in Brownsville, TX (Ellenson et al. 1997) for fine particulate matter, elements, and VOCs indicating the dominance of regional influences. PM2.5 mass and element concentrations in residential indoor and outdoor air were generally higher in the summer than in the spring. Indoor air concentrations of many species were higher than outdoor air concentrations and were attributed to household activities, ventilation of residences, and track-in of dislodged soils. Evidence of agricultural activities was noted in the occurrence of crop-related pesticides (e.g., malathion and chlorpyrifos) in indoor and outdoor air. Concentrations of common household pesticides (e.g., chlordane, chlorpyrifos, diazinon, heptachlor, and propoxur) were generally higher indoors than outdoors and were also present in house dust. Seasonal comparisons of pesticides and PAHs were also presented using matched residences in spring and summer; VOCs also may have indicated seasonal effects. VOCs (notably propane and butane isomers) and PAHs were higher indoors, presumably due to cooking-related activities.

EFFECT OF SURFACE OZONE EXPOSURES ON VEGETATION GROWN IN THE SOUTHERN APPALACHIAN MOUNTAINS: IDENTIFICATION OF POSSIBLE AREAS OF CONCERN

Abstract The results described in this paper are derived from an analysis, for the 8-yr period 1983–1990, that combined experimental exposure-response effects data for deciduous and coniferous seedlings and/or trees with characterized 03 ambient exposure data for a local area and soil moisture to identify areas that may be at risk in the Southern Appalachian Mountains. Results from seedling and tree experiments operated in open-top chambers were used to characterize 0 3 exposure regimes that resulted in growth loss under controlled conditions. Available 0 3 monitoring data were characterized for the states of Alabama, Georgia, South Carolina, North Carolina, West Virginia, Tennessee, Kentucky, and Virginia, using the W126 biologically based cumulative exposure index. As a part of the analysis, both the occurrences of hourly average 03 concentrations ⩾ 0.10 ppm and the soil moisture conditions in the geographic area were considered. Combining exposure information with moisture availability and experimental exposure-response data, the extreme northern and southern portions of the Southern Appalachian area were identified as having the greatest potential for possible vegetation effects. The study was based mostly on results from individual tree seedlings grown in chambers and pots and additional research is needed to identify what differences in effects might be observed if exposures were similar to those experienced in forests. Furthermore, we recommend future investigations to verify the location and presence of specific vegetation species and amounts and whether actual growth losses occurred in those areas of concern that have been identified in this study.

Ozone, sulfur dioxide, and nitrogen dioxide trends at rural sites located in the united states

Abstract We have investigated the existence of trends for ozone, sulfur dioxide, and nitrogen dioxide at rural sites in the U.S. For the ozone analysis, at 54 of the 77 sites (70%) for the 10-year analysis (1979–1988) and at 118 of 147 sites (80%), with at least 4 years of data for the 5-year analysis (1984–1988), there was no indication of trends, either positive or negative. For the 10-year analysis, ozone sites in the Southern and Midwest forestry regions showed more positive than negative signiicant slope estimates. For the 5-year analysis, similar results were obtained, except that the mid-Atlantic region also experienced more positive than negative significant slope estimates. In most of the agricultural regions, there were not many significant trends in either the 10- or 5-year analysis. However, for the agricultural Appalachian region, 50% and 34% of the trends, respectively, were significant and there were more positive than negative significant ozone trends for both the 10- and 5-year periods. For sulfur dioxide, there was an indication of trends at 37 of 64 sites (58%) for the 10-year analysis (1978–1987). For the 5-year analysis (1983–1987), with at least 4 years of data, there was no indication of trends at 115 of 137 sites (84%). For sites in some regions of the U.S., there is an indication that sulfur dioxide concentrations have declined for both the 5- and 10-year periods, but the rate of decline on an aggregate basis has slowed in the 5-year period. There is a strong indication that the sulfur dioxide level decreased at many sites in the Midwest forestry and the Corn belt agricultural regions for the 10-year period. In the Southern forestry and Appalachian agricultural regions, many sites showed a decrease in the index for the 10-year, but not the 5-year, period. The lack of monitoring data for nitrogen dioxide made any conclusion extremely tenuous.

Important Considerations for Establishing a Secondary Ozone Standard to Protect Vegetation

Based on recent evidence published in the literature, as well as retrospective studies using data from the National Crop Loss Assessment Network (NCLAN), cumulative indices can be used to describe exposures of ozone for predicting agricultural crop effects. However, the mathematical form of the standard that may be proposed to protect crops does not necessarily have to be of the same form as that used in the statistical or process oriented mathematical models that relate ambient ozone exposures with vegetation effects. This paper discusses the limitations associated with applying a simple statistic that may take the place of a more biologically meaningful exposure parameter. While the NCLAN data have been helpful in identifying identifying indices that may be appropriate for establishing exposure-response relationships, the limitations associated with the NCLAN protocol need to be considered when attempting to apply these relationships in the establishment of a secondary national ambient air quality standard. The Weibull model derived from NCLAN experiments must demonstrate its generality and universal applicability. Furthermore, its predictive power must be tested using independent sets of field data.

The characterization and comparison of ozone exposure indices used in assessing the response of loblolly pine to ozone

Abstract Using the 1988 and 1989 experimental results obtained for two loblolly pine half-sibling families (GAKR 15–23 and GAKR 15–91) at the Auburn University intensive field research site, we: (1) explored the performance of a set of exposure indices; (2) characterized the ambient air and charcoal-filtered air treatments at Auburn and compared the values of the O3 exposure indices with those values calculated for ambient O3 monitors for a select set of sites; (3) identified and characterized O3 treatments in the Auburn open-top exposure chambers where an adverse effect was noted; and (4) identified where such experimental exposure regimes occurred under ambient conditions. We found that the SUMO exposure index did not perform adequately. We were unable to distinguish among the performances of the SUM06, W126, and SUM08 exposure indices. The results of the analyses of six estimated logistic parameters for a model of diameter2 × height (d2h) vs time indicated O3 effects for both families. At pH 4.3 (near ambient conditions), a response to O3 was detected in the NF × 2.5 treatments for both families for t2, the approximate time of maximum growth during the second year. Using ln (final d2h), family 23 did not show O3 effects. A comparison of the exposures experienced in the NF × 2.5 treatments with those occurring under ambient conditions at other locations showed that in 1983 and 1986, the San Bernardino County (CA) site experienced O3 exposures similar to those values experienced at the NF × 2.5 treatments in 1989.

An alternative form and level of the human health ozone standard

Controlled human laboratory studies have shown that there is a disproportionately greater pulmonary function response from higher hourly average ozone (O3) concentrations than from lower hourly average values and thus, a nonlinear relationship exists between O3 dose and pulmonary function (FEV1) response. The nonlinear dose–response relationship affects the efficacy of the current 8-h O3 standard to describe adequately the observed spirometric response to typical diurnal O3 exposure patterns. We have reanalyzed data from five controlled human response to O3 health laboratory experiments as reported by , Adams (), and . These investigators exposed subjects to multi-hour variable/stepwise O3 concentration profiles that mimicked typical diurnal patterns of ambient O3 concentrations. Our findings indicate a common response pattern across most of the studies that provides valuable information for the development of a lung function (FEV1)–based alternate form for the O3 standard. Based on our reanalysis of the realistic exposure profiles used in these experiments, we suggest that an alternative form of the human health standard, similar to the proposed secondary (i.e., vegetation) standard form, be considered. The suggested form is an adjusted 5-h cumulative concentration weighted O3 exposure index, which addresses both the delay associated with the onset of response (FEV1 decrement) and the nonlinearity of response (i.e., the greater effect of higher concentrations over the mid- and low-range values) on an hourly basis.

Techniques to assess cross-border air pollution and application to a US-Mexico border region

A year-long assessment of cross-border air pollution was conducted in the eastmost section of the US-Mexico border region, known as the Lower Rio Grande Valley, in South Texas. Measurements were conducted on the US side and included fine particle mass (PM2.5) and elemental composition, volatile organic compounds (VOCs) and meteorology. Wind sector analyses of chemical tracers and diagnostic ratios, in addition to principal component analysis (PCA), were initially applied to assess cross-border and overall air shed influences. Linear-angular correlation statistics [Biometrika, 63, (1976), 403-405] and nonparametric multiple comparisons between wind sectors were computed with the particle element data using principal component scores from PCA to determine the direction of source classes. Findings suggest crustal particles and salts carried or stirred by sea breeze winds from a southerly and southeasterly direction from the Gulf of Mexico heavily influenced the elemental composition of the particulate samples. Pair-wise comparisons of wind directions for the principal component scores suggest possible oil combustion influences from utilities or boilers coming from the south and possible coal combustion influences from the north and northwest. The techniques discussed can provide a methodology to assess future ambient levels and cross-border influences in the Valley as conditions change.

The characterization of ozone concentrations at a select set of high-elevation sites in the eastern United States.

Hourly averaged data for ozone collected in 1986 and 1987 were analyzed and characterized for a select set of high-elevation sites in the eastern United States. Pressure-corrected adjustments may be necessary when comparing ozone concentrations measured at two different elevations. When unadjusted concentrations (i.e. in units of parts per million) were used, the Whiteface Mountain sites showed what appeared to be an ozone elevational gradient. A gradient was not observed for the two MCCP Shenandoah National Park sites (SH1 and SH2). When adjusted ozone values (i.e. in units of micrograms per cubic meter) were used, the elevational gradient reported for Whiteface Mountain was no longer observed. When unadjusted concentrations were used, in most cases the high-elevation sites appeared to be receiving greater ozone exposure than the nearby, lower elevation sites. When adjusted ozone values were used, a consistent conclusion was not evident. On a regional basis for the period May through September 1987, when unadjusted concentrations were used, the high-elevation sites in the South appeared to experience higher cumulative ozone exposures than sites in the North. When adjusted ozone values were used, the geographic gradient was not strong. Assuming that target sensitivity remains nearly constant as elevation changes, adjusted concentrations should be taken into consideration when evaluating the relationship between ozone exposures at high-elevation sites and biological effects.

An environmental scoping study in the lower Rio Grande Valley of Texas : I. Comparative assessment of air sampling methods

Abstract The atmospheric monitoring component of the 1993 Lower Rio Grande Valley Environmental Scoping Study measured a wide range of pollutant species from different sampling and analysis methods. Extensive QA/QC activities were also conducted on the sampling and analysis techniques. This enabled a unique comparison of these methods to provide insights into air sampling for larger, long-term exposure monitoring studies. Pollutants monitored were particulate mass and elements, acidic gases, volatile organic compounds, pesticides, and polycyclic aromatic hydrocarbons. This included collocated monitoring devices which monitored same-species pollutants. Sample collection efficiencies of certain atmospheric pollutants are discussed. Finally, data from two sites located in the Lower Rio Grande Valley are also presented and compared.