George M. Sverdrup

Atmospheric and Tributary Inputs of Toxic Substances to Lake Erie

Abstract This paper reports an evaluation of the input of toxic chemicals to Lake Erie in precipitation, in particle and vapor dry deposition, in the Detroit River, and in other Canadian and U.S. tributaries. Results are shown for 13 toxic chemicals for which all or nearly all of these input pathways could be evaluated. The percentage of direct atmospheric contributions relative to total input to Lake Erie calculated for the 13 species are: PCBs, 26%, PAHs, 21%; benzo-a-pyrene, 66%; hexachlorobenzene, 9%; 2,3,7,8-TCDD, 2%; 2,3,7,8-TCDF, 38%; mercury, 22%; lead, 23%; cadmium, 59%; chromium, 17%; arsenic, 8%; dieldrin, 34%; DDT, 29%. For most species the Detroit River was the major input pathway. Vapor phase fluxes out of the lake are indicated for mercury, and for several organic chemicals. Volatilization of PCBs, DDT, and mercury out of the lake is reduced in winter relative to summer, and the vapor flux of PAHs changes direction from volatilization in summer to deposition in winter. The main conclusion of this study is that atmospheric input to Lake Erie may be a significant contributor of certain toxic chemicals.

Variability of hazardous air pollutants in an urban area

Abstract The variability of hazardous air pollutants (HAPs) is an important factor in determining human exposure to such chemicals, and in designing HAP measurement programs. This study has investigated the factors which contribute to HAP variability in an urban area. Six measurement sites separated by up to 12 km collected data with 3 h time resolution to examine spatial variability within neighborhoods and between neighborhoods. The measurements were made in Columbus, OH. The 3 h results also were used to study temporal variability, and duplicate samples collected at each site were used to determine the component of variability attributable to the measurement process. Hourly samples collected over 10 days at one site provided further insight into the temporal resolution needed to capture short-term peak concentrations. Measurements at the 6 spatial sites focused on 78 chemicals. Twenty-three of these species were found in at least 95% of the 3 h samples, and 39 chemicals were present at least 60% of the time. The relative standard deviations for most of these 39 frequently detected chemicals was 1.0 or lower. Variability was segmented into temporal, spatial, and measurement components. Temporal variation was the major contributor to HAP variability for 19 of the 39 frequently detected compounds, based on the 3 h data. Measurement imprecision contributed less than 25% for most of the volatile organic species, but 30% or more of the variability for carbonyl compounds, trace elements, and particle-bound extractable organic mass. Interestingly, the spatial component contributed less than 20% of the total variability for all the chemicals except sulfur. Based on the data with hourly resolution, peak to median ratios (hourly peak to 24 h median) averaged between 2 and 4 for most of the volatile organic compounds, but there were two species with peak to median ratios of about 10.

Comparison of particles taken from the ESP and plume of a coal-fired power plant with background aerosol particles

Abstract In order to determine the biological effects of plume flyash arising from the emissions of a coalfired power plant, a major study is underway to develop an in-plume sampling capability in order to collect a sufficient quantity of material to permit toxicological testing. To ascertain the effects of plume flyash, it is necessary to be able to determine that the collected particles were emitted from the plant and are distinguishable from the background aerosol particles. It is also of interest to compare the plume particles with those collected by the electrostatic precipitator (ESP). Samples of both in-plume and background aerosol particles were collected from a helicopter. Preliminary experiments were conducted to determine if computer-controlled scanning electron microscopy (CCSEM) can be used to examine such in-plume samples and to relate the observed particle types to the conditions under which they were collected.

SMOG chamber studies of NOx chemistry in power plant plumes

Smog chamber simulations have been conducted in a 17m3 irradiation chamber with the purpose of identifying the effects of five independent variables on the transformation rates and product distributions of nitrogen and sulfur species in dilute power plant plumes. The study was designed to simulate the conditions in a plume starting at the point where half the NO has been oxidized to NO2, where the plume will have been extensively diluted with background air containing hydrocarbons and ozone. The variables studied include: (1) plume hydrocarbon/NOx ratio; (2) composition of organics in the diluting air; (3) NOx/SO2 ratio; (4) relative humidity; (5) presence of pre-existing acid sulfate aerosol. The starting concentrations and ratios of plume constituents were based on actual plume data. The results of the study are presented in terms of the impact of the independent variables on the extent of NOx conversion to products, the rate of NOx and SO2 transformation to products and the relative distribution of gaseous and aerosol nitrate products. Briefly, the NOx transformation rate is found to be dependent on hydrocarbon composition, hydrocarbon/NOx ratio and relative humidity. The rates are essentially independent of SO2 concentration or the presence of pre-existing H2SO4 aerosol surface. The SO2 transformation rate appears to be independent of all five independent variables. The distribution of the nitrate products, nitric acid, peroxyacetyl nitrate and paniculate nitrate is a function of HC composition, HC/NOx ratio and irradiation time. The effects of HC composition and HC/NOx ratio decrease at the longer irradiation times characteristic of transport conditions.

Modeling study of the potential importance of heterogeneous surface reactions for NOx transformations in plumes

A parametric model of gas-particle surface reactions is incorporated into a reactive plume model and used to assess the potential importance of heterogeneous surface reactions on gas phase plume chemistry. Heterogeneous loss of the following species is found to be potentially significant: H2O2, PAN, NO3, N2O5, OH, HO2 and in cold weather HO2NO2. This simple model is unable to account for equilibrium/capacity effects in the condensed phase and therefore cannot be used for SO2 and HNO3 reaction with aerosol surface.

Determination of submicrometer particle size distributions across a power plant plume

Abstract Submicrometer particle size distributions were spatially resolved across a power plant plume by inversion of the outputs of three continuous particle sensors. Total submicrometer particle surface and volume concentrations closely followed the SO2 profile. Particle concentrations in the nuclei size range 0.008–0.05 μm increased from background values to maxima in the plume edges. Nuclei concentrations were depressed in the plume center in the presence of increased particle surface concentration in the accumulation 0.05–1.0μm size range.