Chester W. Spicer

Unexpectedly high concentrations of molecular chlorine in coastal air

The fate of many atmospheric trace species, including pollutants such as nitrogen oxides and some volatile organic compounds, is controlled by oxidation reactions. In the daytime troposphere, these reactions are dominated by photochemically produced OH radicals; at night and in polluted environments, NO3 radicals are an important oxidant. Ozone can contribute to the oxidation of atmospheric species during both day and night. In recent years, laboratory investigations, modelling studies, measured Cl deficits in marine aerosols and species-nonspecific observations of gaseous inorganic chlorine compounds other than HCl have suggested that reactive halogen species may contribute significantly to—or even locally dominate—the oxidative capacity of the lower marine troposphere. Here we report night-time observations of molecular chlorine concentrations at a North American coastal site during onshore wind flow conditions that cannot be explained using known chlorine chemistry. The measured Cl2 mixing ratios range from <10 to 150 parts per 1012 (p.p.t.), exceeding those predicted for marine air by more than an order of magnitude. Using the observed chlorine concentrations and a simple photochemical box model, we estimate that a hitherto unrecognized chlorine source must exist that produces up to 330 p.p.t. Cl2 per day. The model also indicates that early-morning photolysis of molecular chlorine can yield sufficiently high concentrations of chlorine atoms to render the oxidation of common gaseous compounds by this species 100 times faster than the analogous oxidation reactions involving the OH radical, thus emphasizing the locally significant effect of chlorine atoms on the concentrations and lifetimes of atmospheric trace species in both the remote marine boundary layer and coastal urban areas.

Nitric acid measurement methods: An intercomparison☆

Abstract An interlaboratory comparison of methods to measure gaseous nitric acid is described. Field experiments were conducted in Claremont, CA in late August and early September of 1979. Ten nitric acid measurement methods were compared during the 8 day field experiment. Six different research groups participated in the nitric acid measurements. The methods compared include 2 which employed chemiluminescence principles, 1 infrared, 2 diffusion denuder and 5 filtration techniques. The 8 study days were divided into 32 sampling intervals of 3, 6 and 12 h. Based on the median of the 10 methods, the nitric acid concentration ranged from 1.85 to 37.05μ gm −3 . The nitric acid concentration was highly correlated with other photochemical pollutants such as O 3 and PAN, and all three were strongly correlated with temperature and solar intensity. On the average, gaseous nitric acid and paniculate nitrate contributed equally to the total inorganic nitrate burden at the site. Of the 10 methods investigated, 5 exhibited excellent agreement with the median nitric acid concentration, 2 yielded slopes significantly exceeding 1.0 and 3 suffered from problems which resulted in relatively poor agreement with nitric acid concentration. A great many chemical and meteorological variables were measured during the study, and the effects of these ancillary variables on the nitric acid measurement methods are discussed.

Photochemical atmospheric pollutants derived from nitrogen oxides

Abstract Concern is now being focused on the health effects of nitrogen oxides and nitrogen oxides reaction products in the atmosphere. This paper reviews 3 years of investigation into the formation, distribution and fate of the nitrogen oxides and their reaction products. Smog-chamber and field-monitoring studies of the nature and concentration of gaseous and particulate nitrogen compounds are described, along with pertinent problems in analytical methodology.

Particulate nitrate: Laboratory and field studies of major sampling interferences

Abstract Particulate nitrate is a significant constituent of the atmosphere. Its accurate determination is important in assessing its impact on health, visibility, and precipitation chemistry. This report describes a study of particulate nitrate sampling interferences. Serious interference was found to be caused by collection of gaseous nitrogen compounds on niters used for nitrate sampling. Both laboratory and field experiments are presented which document the severity of the interference. Other factors having a potential effect on nitrate sampling are also discussed.

Source attribution of ambient air toxic and other VOCs in Columbus, Ohio

Abstract Chemical mass balance (CMB) source apportionment modeling was conducted on a data set of 142 3 h integrated air samples collected at 6 different sites in 3 separate campaigns during the summer of 1989 in Columbus, Ohio; source contributions to 19 light hydrocarbon and toxic VOC species, including formaldehyde and acetaldehyde, were modeled. Overall, the results indicated that area sources, and in particular vehicle exhaust and organic solvent usage by small industrial/commercial facilities, are important contributors to the major toxic VOCs measured in urban air. In addition, the temporal resolution of the measurements allowed a number of observations regarding the short-term variability of these area sources, including diurnal trends in vehicle exhaust, gasoline vapor, and natural gas sources. The natural gas source was identified as a significant source of light hydrocarbons in the Columbus area, a finding similar to that of several other recent source apportionment studies of VOCs in urban areas. The temporal and spatial variability in gasoline vapor contributions suggested that the source is associated more with mobile sources (running losses, evaporative emissions from vehicles), rather than with fixed sites such as service stations. Finally, CMB modeled source contributions were coupled with a simple box model of the study area to provide estimates of the emission rates of various area sources. The results of these calculations suggest that there are probably substantial emissions from area sources that are not included in current emissions inventories.

Nitrogen Oxide Reactions in the Urban Plume of Boston

The rate of removal or conversion of nitrogen oxides has been determined from airborne measurements in the urban plume of Boston. The average pseudo-first-order rate constant for removal was 0.18 per hour, with a range of 0.14 to 0.24 per hour under daylight conditions for four study days. The removal process is dominated by chemical conversion to nitric acid and organic nitrates. The removal rate suggests an atmospheric lifetime for nitrogen oxides of about 5 to 6 hours in urban air.

Interferences in sampling atmospheric particulate nitrate

Abstract The vast majority of atmospheric data on particulate nitrate concentrations is based on filter collections employing glass fiber filters. Recent laboratory studies indicate that these data may be in error due to collection of gaseous nitrates and nitrate precursors on the filters. This communication documents the severity of the interference under ambient sampling conditions. Two types of glass fiber filters in widespread use were found to collect 10–20 times as much artifact nitrate as actual particulate nitrate.

Transformations, lifetimes, and sources of NO2, HONO, and HNO3 in indoor environments

Recent research has demonstrated that nitrogen oxides are transformed to nitrogen acids in indoor environments, and that significant concentrations of nitrous acid are present in indoor air. The purpose of the study reported in this paper has been to investigate the sources, chemical transformations and lifetimes of nitrogen oxides and nitrogen acids under the conditions existing in buildings. An unoccupied single family residence was instrumented for monitoring of NO, NO2, NOy, HONO, HNO3, CO, temperature, relative humidity, and air exchange rate. For some experiments, NO2 and HONO were injected into the house to determine their removal rates and lifetimes. Other experiments investigated the emissions and transformations of nitrogen species from unvented natural gas appliances. We determined that HONO is formed by both direct emissions from combustion processes and reaction of NO2 with surfaces present indoors. Equilibrium considerations influence the relative contributions of these two sources to the indoor burden of HONO. We determined that the lifetimes of trace nitrogen species varied in the order NO approximately HONO > NO2 > HNO3. The lifetimes with respect to reactive processes are on the order of hours for NO and HONO, about an hour for NO2, and 30 minutes or less for HNO3. The rapid removal of NO2 and long lifetime of HONO suggest that HONO may represent a significant fraction of the oxidized nitrogen burden in indoor air.

An assessment of the luminol chemiluminescence technique for measurement of NO2 in ambient air

Abstract The detection of NO2 by its chemiluminescent reaction with luminol is a rapid and sensitive means of measuring atmospheric NO2. However, testing and field use of a commercial NO2 monitor employing this detection scheme have shown that several corrections are necessary in order to obtain accurate NO2 data at low concentrations. In use aboard aircraft, the NO2 data must be corrected for zero offset, altitude (i.e. pressure), nonlinearity of response, and interferences from ozone and PAN. Detector response is dependent on the age of luminol reagent solution. This paper describes the tests performed to determine correction factors, the algorithms and order of precedence for applying the corrections, and other observations regarding detector performance.

Peroxyacetyl nitrate solubility and decomposition rate in acidic water

Abstract Recent investigations have shown that peroxyacetyl nitrate (PAN) is soluble in acidic water samples. A Henrys law constant of 5 ± 1 M atm −1 has been determined. PAN decays in a first order manner in these solutions, with k = 7.0 ± 0.3 × 10 −3 min −1 at 5°C. The principal anionic product was nitrate ion.