Steven H. Cadle

Nitric acid and ammonia in urban and rural locations

Abstract Measurements of ammonia, nitric acid and particulate nitrate were made at urban sites in Commerce City, Colorado, and Warren, Michigan and at rural locations near Abbeville, Louisiana and Luray, Virginia. The average ammonia and nitric acid concentrations over all sites were 1.7 ppb and 0.7 ppb, respectively. Diurnal patterns, determined at the Abbeville site, suggested a photochemical mechanism for the production of nitric acid and local sources for ammonia. Seasonal data collected in Warren, Michigan showed ammonia concentrations were lowest in the winter. This appears to be caused by the temperature dependence of the ammonium nitrate equilibrium constant. Ammonia and nitric acid concentrations at the other sites were not in agreement with the concentrations predicted from the ammonium nitrate equilibrium constant.

The Denver Winter Aerosol: A Comprehensive Chemical Characterization

The sampling and chemical analysis of the ambient aerosol collected in Denver, CO, for a 40-day period during November and December, 1978 are described in this report. Parameters included 12-hr TSP measurements, 24-hr respirable and inhalable mass measurements, and 4-hr measurements of mass and chemical species (NO3−, SO4 =, NH4 +, organic and elemental carbon as well as 13 chemical elements) in two size fractions i.e., less than 2.5 μm diameter (fine fraction) and larger than 2.5 μm diameter (coarse fraction). On the basis of the chemical analyses, it was possible to account for all particulate mass in both size fractions. In the fine fraction, the major constituents were organic carbon (21.6%), NH4NO3 (20.0%), elemental carbon (15.3%), (NH4)2SO4 (13.6%), and the remainder consisted primarily of soil-like material, lead salts, and adsorbed water. Three quarters of the coarse fraction consisted of soil-like material, with the remainder composed of the same species that dominated the fine fraction.

Atmospheric concentrations and the deposition velocity to snow of nitric acid, sulfur dioxide and various particulate species

Abstract A study of deposition velocities to snow was conducted during the 1982–1983 and 1983–1984 winters at the University of Michigan Biological Station in northern Michigan. Weekly measurements were made of dry deposition rates to snow and the atmospheric concentrations of the depositing species. SO 2 , with an average concentration of 2.2 ppb, was the dominant atmospheric sulfur containing species. NO 2 , with an average concentration of 1.8 ppb, was the dominant atmospheric nitrogenous species. NO − 3 deposition was due primarily to HNO 3 , which averaged 0.2 ppb. The HNO 3 deposition velocity averaged 1.4cm s −1 . The SO 2 deposition velocity varied with temperature, averaging 0.15 cm s −1 for samples with appreciable exposure time above − 3°C, and 0.06 cm s −1 for samples which remained below an ambient temperature of −3°C. Deposition velocities of Ca 2+ , Mg 2+ , Na + , K + and NH + 4 were 2.1, 1.5, 0.44, 0.51 and 0.10cm s −1 , respectively. The mass median diameters of these species were 4.4, 2.7, 1.8, 0.9 and 0.46 μm, respectively.

Problems in the sampling and analysis of carbon particulate

Abstract Several thermal and wet chemical methods of separating organic from elemental carbon in particulate samples were examined. It is concluded that none of them represents an ideal separation procedure and that only a method-dependent operational definition of organic and elemental carbon is possible at this time. The best separation method appears to be a thermal procedure using 350°C air oxidation followed by pyrolysis in He at 950°C. There are also difficulties in sampling since dual filter techniques show that adsorption of organic compounds on various filter media accounted for at least 15 per cent of the total organic carbon collected during ambient sampling in Warren, MI. This adsorption further confuses the results and needs to be studied at other sampling sites.

Remote sensing measurements of carbon monoxide emissions from on-road vehicles

This report describes instrumentation that remotely measures the CO emissions from thousands of vehicles per day with a sensitivity of ± 1 percent CO in the exhaust, which is approximately 13 grams per mile of CO for new vehicles. A prototype of this instrument was used in Denver, Colorado in January 1989 during a study conducted in conjunction with researchers from the University of Denver, who have developed similar Instrumentation. Emission measurements were made on approximately 4000 vehicles that were identified by make and model year from state vehicle registration records. The data demonstrates a clear trend of higher emission rates from older vehicles and suggests that lowering emission standards for new vehicles will have little immediate impact upon ambient urban CO levels.

Chemical analysis of size-segregated samples of Denver's ambient particulate

Size-segregated impactor samples of Denvers wintertime airborne particulate were analyzed for the major chemical species. These species are responsible for most of the pollution-related visibility reduction in Denver. Samples were collected three times a day during a 40-day field program in November-December, 1978. Each of the measured chemical species (sulfate, nitrate, ammonium, bromide, organic and elemental carbon) had a log-normally distributed accumulation mode with a mass median aerodynamic diameter near 0.3 ..mu..m. For all species, particle size increased with increasing relative humidity. These results are supported by electrical aerosol analyzer (EAA) measurements. The impactor results for this time period are consistent with a photochemical mechanism for particulate nitrate formation and a heterogeneous mechanism for the formation of sulfate particles. 23 references, 5 figures, 5 tables.

Low molecular weight aliphatic amines in exhaust from catalyst-equipped cars

Emissions from automobiles equipped with three-way catalysts were studied. Aliphatic amine emissions from the cars tested were less than 2.2 mg/mi. Emissions of monomethylamine and dimethylamine were no more than 0.3 mg/mi and 0.1 mg/mi respectively. It is unlikely that any standard gasoline-propelled cars emit significant quantities of amines. (1 diagram, 1 graph, 20 references, 6 tables)

Particulate Carbon at Various Locations in the United States

Particulate elemental and organic carbon concentrations were determined on filters collected between 1972 and 1980 at ten United States’ sites representing urban, suburban, rural, and remote areas. The results showed that particulate elemental carbon is ubiquitous with mean concentrations ranging from 1.1 micrograms per cubic meter at the remote site in South Dakota to 13.3 micrograms per cubic meter in a congested area in New York City. About 80% of the elemental carbon mass consists of particles with a diameter of less than 2.5 micrometers. Particulates in this size range are responsible for most pollutant-related visibility reductions. Since it appears that elemental carbon is the only light-absorbing particulate species, the specific light-absorption coefficient for elemental carbon was calculated to be 12.7 m2/g while the specific light-scattering coefficient was 3.2 m2/g. Using these coefficients, the contributions of elemental carbon to the observed visibility reduction at the various sites are estimated. These range from 6 to 38%. Also discussed are the seasonal and diurnal variations of particulate elemental and organic carbon as well as the contribution from secondary organic particulates. In addition, an updated carbon-source apportionment, based on recent analytical developments, is presented for the Denver area.

Retention and release of chemical species by a Northern Michigan snowpack

Snowcore and water samples were collected during the 1981 to 82 winter at two independent sites in Northern Michigan; the Little Pigeon River and McNearney Lake. Acidic and basic species were determined in all samples. Examination of the concentration vs depth profiles of snow cores showed that all species were stable in the snowpack until the spring thaw period. During the thaw, 50 to 70% of the stored acids were released during the first 20% of the snowmelt. However, rainfall during the melt period contributed as much acidity to the environment as the snowmelt. Study of runoff showed that only 30% of the nitrate originally present in the snowpack appeared in the Little Pigeon River. Therefore, H2SO4 dominated the runoff acidity at the Little Pigeon River. Both nitrate and sulfate were responsible for the slight acidification of McNearney Lake during the snowmelt period.

Urban dew: Its composition and influence on dry deposition rates

Abstract The composition of dew collected from a Teflon surface was compared to summer rainwater concentrations at a site in Warren, MI. This comparison showed that natural dew is similar to rainwater with the exception that dew has much higher concentrations of Ca 2+ and Cl − and much lower acidity. Dry deposition rates of several species were measured to artificially-generated dew and a dry surface. It was found that deposition rates were 2–20 times greater to the artificial dew than to the dry surface, indicating that the presence of dew enhances both the retention of dry deposited particles and the absorption of water soluble gases. Measurement of the atmospheric concentrations of the depositing gases permitted the calculation of deposition velocities for particulate Cl − , NO − 3 , SO 2− 4 , Ca 2+ , Mg 2+ , Na + , K + and NH + 4 . Deposition velocities for gaseous HNO 3 , HCl, SO 2 and NH 3 were also determined after correction for particle deposition. These results indicate that acid dew is not a problem at this site. However, the ability of dew to increase the deposition rates of acids and acid precursors to some surfaces suggests that dew may be more acidic at sites with lower deposition rates of basic particles.