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To evaluate plant and herbivore responses to nitrogen we conducted a fertilization study at a low and high pollution site in the mixed conifer forests surrounding Los Angeles, California. Contrary to expectations, discriminant function analysis of oak herbivore communities showed significant response to N fertilization when atmospheric deposition was high, but not when atmospheric deposition was low. We hypothesize that longer-term fertilization treatments are needed at the low pollution site before foliar N nutrition increases sufficiently to affect herbivore communities. At the high pollution site, fertilization was also associated with increased catkin production and higher densities of a byturid beetle that feeds on the catkins of oak. Leaf nitrogen and nitrate were significantly higher at the high pollution site compared to the low pollution site. Foliar nitrate concentrations were positively correlated with abundance of sucking insects, leafrollers and plutellids in all three years of the study.

The forests surrounding the urban areas of the Los Angeles basin are impacted by ozone and nitrogen pollutants arising from urban areas. We examined changes in the herbivore communities of three prominent plant species (ponderosa pine, California black oak and bracken fern) at six sites along an air pollution gradient. Insects were extracted from foliage samples collected in spring, as foliage reached full expansion. Community differences were evaluated using total herbivore abundance, richness, Shannon-Weiner diversity, and discriminant function analysis. Even without conspicuous changes in total numbers, diversity or richness of herbivores, herbivore groups showed patterns of change that followed the air pollution gradient that were apparent through discriminant function analysis. For bracken fern and oak, chewing insects were more dominant at high pollution sites. Oak herbivore communities showed the strongest effect. These changes in herbivore communities may affect nutrient cycling in forest systems.

During January-March of 1990 a study was conducted to determine the sources of sulfur oxides present at Canyonlands and Green River, Utah. Samples were collected at these two receptor sites and at several sites intended to characterize the chemical composition of air masses reaching the receptor sites from various geographical regions. The results of the sampling program have been given in the first paper in a series of three papers. In this paper, the concentrations of spherical aluminosilicate (SAS) particles, total fluoride, and particulate selenium, arsenic and lead are combined with meteorological data to obtain source fingerprints for the ratios of these species to SO x , from the various regional sources that can influence the Canyonlands sampling site. The results indicate that the variability in the ratios of these various species to SO x , from the various regional sources is large enough to provide useful input to a receptor based, chemical mass balance source apportionment of SO, at the receptor sites. The chemical mass balance analysis is given in the final paper of this series. The ratio of SAS: SO x , varies by a factor of 25 in emissions from various coal-fired power plants. The concentrations of lead and arsenic relative to sulfur oxides is also variable in emissions from different coal-fired power plants. The ratio of particulate selenium and total fluoride to SO x , in emissions from these coal-fired sources is relatively constant. Emissions from source regions containing smelters are high in Se, As and Pb. Emissions from source regions containing fluoride ore processing industries have a high F Tots; : SO x , ratio.

Spherical aluminosilicate (SAS) particles, total fluoride and particulate trace elements are potential endemic tracers for determining and quantifying the presence of coal-fired power plant and other sulfur oxide source emissions at far downwind distances. These endemic tracers, and sulfate and SO 2 were collected at Canyonlands National Park, at seven ambient sampling sites located in air mass transport paths to Canyonlands and from the stacks of coal-fired power plants in central Utah during January-March of 1990 for use in source apportionment analyses. These data have been combined with results obtained in concurrent studies by the National Park Service (EPIC study) and Salt River Project to provide a complete data set for the characterization of the regional and point sources that can influence air quality in the Canyonlands area. This paper gives details on the study design and on the chemical composition of fine particulate matter in the study area. While concentrations of SO x (SO 2 (g) plus particulate sulfate) were in good agreement among the various studies, accurate concentrations for sulfate and SO 2 were only obtained using a diffusion denuder sampling system because of the absorption of SO 2 (g) by particles in all filter pack sampling systems. Concentrations of FT Total (HF(g) plus particulate fluoride), and particulate Se, As, and Pb determined by multiple techniques were generally in good agreement. Sulfate (assumed present as ammonium sulfate) and nitrate (assumed present as ammonium nitrate) accounted for an average of 19 and 4%, respectively, of the fine particulate mass collected at Canyonlands and 8 and 2% of the fine particulate mass at Green River, Utah. Data were available at the Edge of the Cedars, Utah, sampling site to estimate the complete chemical composition of the fine particles. The average concentration of fine particles at Edge of the Cedars was 15 μg m −3 . Sulfate (as the ammonium salt) averaged 15% of the fine particulate mass, comparable to Canyonlands. Nonsulfate inorganic compounds averaged 58% of the mass. The majority of these inorganic species are background desert particles. The remainder of the mass, 27%, is presumably water, and organic and elemental carbon.

During January-March of 1990 a study was conducted to determine the sources of sulfur oxide emissions present in the Canyonlands area in Utah. Samples were collected at the Island-in-the-Sky visitors center in Canyonlands National Park and at several sites circling the park to characterize the chemical composition of air masses influencing the receptor sites from various geographical regions. The results of the sampling program and the identified chemical fingerprints of the sources that can impact the Canyonlands receptor site have been given in the first two papers in a series of three papers. In this paper are presented the results of chemical mass balance source apportionment of the SOx, present at Canyonlands, Green River, Bullfrog Marina and Edge of the Cedars, Utah, using the chemical composition and source fingerprint data given in the preceding papers. The results indicate that the presence of sulfur oxides at the Canyonlands area is a regional problem not dominated by a single source. The contributions to SOx, at Canyonlands during the 21 days included in the source apportionment analyses included sources to the southwest (37%),south and southeast (20%), north and northeast (19%), and northwest (23%). At the Edge of the Cedars State Park to the southeast of Canyonlands, sources from the southeast contributed 51 % of the observed SOx. At Bullfrog Marina in the Lake Powell National Recreation Area, southwest of Canyonlands, sources to the southwest were responsible for 81 % of the SOx present. At Green River, to the north of Canyonlands, the contribution of sources to the north and northeast were reduced (10%) because the major transport path of sources from these directions was the movement of emission from northwestern Colorado down the Colorado River drainage and south of Green River. The apportionment of sulfate at Canyonlands has been estimated from a combination of the chemical mass balance SOx source apportionment results, the measured concentrations of S02 and particulate sulfate, and meteorological data. This analysis indicates that, while the main source of SOx at Canyonlands is from emissions to the southwest, the main source of sulfate is from SOx emissions originating from the southeast of Canyonlands.