Joseph Forrest

Determination of atmospheric nitrate and nitric acid employing a diffusion denuder with a filter pack

A diffusion denuder assembly for sampling and analyzing atmospheric gaseous and particulate nitrate without significant artifactual error was constructed and evaluated. The system consists of parallel filter packs, one to determine total inorganic nitrate and the other, preceded by a diffusion denuder to remove nitric acid, to measure particulate nitrate. Nitric acid is determined by difference. Ambient sampling data for total nitrate (sum of nitric acid and particulate nitrate) were statistically identical by either high volume or low volume sequential filter packs. Differences between nitric acid and nitrate data by filter pack and diffusion denuder methods were attributed principally to known sources of error in the former-adsorption of HNO3 on collected particles and evaporation of nitric acid from collected ammonium nitrate particles. Negative correlation of particulate nitrate and strong acid levels was observed. During long sampling times adsorption of HNO3 on collected particles is apparently the dominant source of error eliminated by use of the diffusion denuder method; for short sampling times, evaporative loss of NH4NO3 is dominant. Losses of nitrate particles by impaction or ammonium nitrate by evaporation in the denuder appear to be negligibly small for particles ⩽ 3pm.

Uptake of dissolved sulfide by Spartina alterniflora: evidence from natural sulfur isotope abundance ratios

The difference in the stable sulfur isotope ratios of sulfate and sulfide in marsh pore water was used to verify the uptake of hydrogen sulfide by the salt marsh cordgrass Spartina alterniflora in a North Carolina salt marsh. Most of the plant sulfur derived from pore-water sulfide was recovered as sulfate, an indication that the sulfide had been oxidized within the plant. The analysis of the sulfur isotope ratios of other coastal halophytes may be a useful technique for determining whether sulfide is taken up by plants in saline wetlands.

Determination of total inorganic nitrate utilizing collection of nitric acid on NaCl—impregnated filters

Abstract Cellulose filters impregnated with NaCl will collect nitric acid vapor from ambient atmospheres at efficiencies of ~95% when placed downstream from pretreated quartz particle filters in a high-volume sampler. No adsorption of NO2 on the NaCl filters with retention as nitrate was observed. Conversion of NO2 to nitrate on quartz (either retained as nitrate or released as artifact nitric acid) was negligibly low with the removal of the less than 1% of the incident NO2. At high humidities adsorption of HNO3 on the quartz prefilter can become significant Quartz filters which were preloaded with ambient particulate matter lost nitrate when exposed to aerosol H2SO4. Sulfur dioxide may be collected on potassium-carbonate-impregnated cellulose filters placed downstream from quartz and NaCl papers without any loss on the preceding filters. Ammonium nitrate on quartz filters is partially volatilized during ambient air sampling.

The application of an isotopic ratio technique to a study of the atmospheric oxidation of sulfur dioxide in the plume from an oil-fired power plant☆

Abstract The rate of oxidation of sulfur dioxide to sulfate in the plume of an oil fired plant has been studied by sampling with a single engine aircraft. A mechanism is postulated whereby the sulfur dioxide is in equilibrium with water on particulates and subsequently catalytically oxidized to sulfate. Vanadium particulates, originating from the oil, are proposed to serve as a catalyst. A pseudo second order mechanism depending on sulfur dioxide and particulate concentrations is indicated by the data. No dependency on relative humidity was observed. The rate of reaction is 1 ppm −1 h −1 . A new technique employing isotopic ratio measurements was employed in conjunction with simultaneous concentration measurements of sulfur dioxide and sulfate. The method is based on measuring the isotopic ratio of the 32 S: 34 S naturally occurring in the fuel sulfur. Changes were experienced in these ratios due to chemical reactions in the atmosphere. These changes were measured and interpreted as to an implied reaction.

Sampling and analysis of atmospheric sulfur compounds for isotope ratio studies

Abstract A method has been developed for sampling atmospheric oxides and for processing the samples for the determination of stable sulfur isotope ratios. Milligram quantities of oxides were collected with high volume sampler packs consisting of glass fiber filters to retain particulate sulfate and alkaline impregnated papers which absorbed sulfur dioxide. Pretreatment has reduced filter blanks to reasonable levels. The effect of concentration, temperature and humidity upon sampling efficiency is described. Various types and grades of paniculate filters showed a wide range of adsorption of sulfur dioxide with formation of extrinsic sulfate. Modified procedures developed for treating small samples produced pure sulfur dioxide for mass spectrometry. Sulfur concentrations were measured during sample preparation by a 110Ag tracer technique.

Further studies on the oxidation of sulfur dioxide in coal-fired power plant plumes

Abstract Measurements of particulate sulfur to total sulfur concentration ratios and 34 S- 32 S isotope ratios were employed to determine the percent of sulfur dioxide converted to sulfate in the plumes of four coal-fired power plants. A fixed-wing airplane was outfitted with a high-volume impregnated filter assembly to collect the samples. A variety of parameters were investigated including relative humidity ranging from 32 to 85%, temperatures from 10 to 25°C, distances as far as 70km and times as long as 200 min. Generally the extent of SO 2 oxidation seldom exceeded 5% with essentially all of the observed oxidation occurring within the first few kilometers after emission. The observations are interpreted as indicative of a heterogeneous mechanism with the consumption or poisoning of available catalyst. No distinct correlation was found between the extent of sulfur dioxide conversion with distance, travel time, temperature, relative humidity, time of day or atmospheric stability. Plume reproducibility measurements were made, aircraft flight patterns compared and fringe effects investigated. An extensive body of information has been obtained and should serve as a reference for future investigations.

Formation of sulfate, ammonium and nitrate in an oil-fired power plant plume

A series of experiments was performed at the oil-fired Anclote power plant of the Florida Power Corp., Tarpon Springs, Florida. Plume samples at varying downwind locations were obtained by means of a high-volume filter pack. Operational oxygen levels during fuel combustion were varied experimentally; particulate sulfate and sulfuric acid concentrations in both flue gas and plumes increased directly with excess O2 levels. Plume dropout of paniculate sulfate was found to occur during some experiments. A generalized trend toward increasing ammonium content of plume particulates with time was observed. Particulate nitrate formation did not indicate a similar trend. Oxidation of SO2 to sulfate within a time frame of up to 100 min and 50 km ranged within 1–3 %, with but two runs exceeding 3 %. No correlation was found between any individual meteorological parameter and extent of oxidation. A significant difference between conversions during summer and winter runs was observed, conceivably attributable to differences in the vanadium content of the fuel oils and to some extent the combination of higher temperature, relative humidity, water partial pressure and unstable weather during the summer.

Oxidation of sulfur dioxide in the sudbury smelter plume

Abstract The plume data obtained on the extent of oxidation of sulfur dioxide to sulfate from the Sudbury Smelter operation were interpreted as arising from a heterogeneous catalytic pseudo second-order mechanism. The rate of reaction was found to be 0.2 ppm −1 hr −1 . This value is 1/5 that found for the pseudo-second order constant at an oil-fired plume. Of significance to a heterogeneous mechanism was that the emitted particulate loading of 0.04 grams per liter of emitted sulfur dioxide at the smelter operation was lower but possibly only coincidentally exactly equal to 1/5 that of the oil-fired operation.

A comparison of filter, denuder, and real-time chemiluminescence techniques for nitric acid determination in ambient air

Abstract Measurements of gas-phase nitric acid were made by four separate techniques during a 7-day summertime period at a near-coastal site on Long Island, NY. Results from methods intercomparison data for HNO 3 , and their relationship to particulate NO 3 − and other odd N and oxidant species show the following: (a) high-volume filter pack HNO 3 concentrations are well correlated with diffusion denuder difference (DD) results, except for small absolute losses with the former; (b) daytime real-time two-channel chemiluminescence HNO 3 levels correlated well with DD results, but were higher during night-time periods; (c) results by a new Al 2 (SO 4 ) 3 denuder/thermal evolution technique were not in agreement with other techniques. Based on HNO 3 and paniculate NO 3 results reported herein, it appears that negative errors in HNO 3 filter-sampling techniques resulting from HNO 3 loss by sorption generally exceed positive errors NH 4 NO 3 volatilization at this site.

Conversion of sulfur dioxide to sulfate during the da vinci flights

Abstract Simultaneous measurements of atmospheric particulate sulfate and SO2 were made by tandem filter sampling during manned balloon flights. The balloon permitted measurement of chemical species evolution while following a given air mass. On the June 8, 1976, flight, the balloon encountered a relatively stagnant air mass, remaining above St. Louis County for most of the day before being carried off by nocturnal winds. Concentrations of sulfate and SO2 remained relatively constant during an eight-hour period. Processes responsible for concentration changes were examined to set bounds upon the oxidation rate of SO2. The data are consistent with an oxidation rate as low as zero and no greater than 4% h−1.