Showing papers in "Journal of Atmospheric Chemistry in 1989"

Global distribution of natural freshwater wetlands and rice paddies, their net primary productivity, seasonality and possible methane emissions

Abstract: A global data set on the geographic distribution and seasonality of freshwater wetlands and rice paddies has been compiled, comprising information at a spatial resolution of 2.5° by latitude and 5° by longitude. Global coverage of these wetlands total 5.7×106 km2 and 1.3×106 km2, respectively. Natural wetlands have been grouped into six categories following common terminology, i.e. bog, fen, swamp, marsh, floodplain, and shallow lake. Net primary productivity (NPP) of natural wetlands is estimated to be in the range of 4–9×1015 g dry matter per year. Rice paddies have an NPP of about 1.4×1015 g y−1. Extrapolation of measured CH4 emissions in individual ecosystems lead to global methane emission estimates of 40–160 Teragram (1 Tg=1012 g) from natural wetlands and 60–140 Tg from rice paddies per year. The mean emission of 170–200 Tg may come in about equal proportions from natural wetlands and paddies. Major source regions are located in the subtropics between 20 and 30° N, the tropics between 0 and 10° S, and the temperate-boreal region between 50 and 70° N. Emissions are highly seasonal, maximizing during summer in both hemispheres. The wide range of possible CH4 emissions shows the large uncertainties associated with the extrapolation of measured flux rates to global scale. More investigations into ecophysiological principals of methane emissions is warranted to arrive at better source estimates.

Organic matter of the troposphere - V: Application of molecular marker analysis to biogenic emissions into the troposphere for source reconciliations.

Abstract: Organic matter in tropospheric aerosols is derived from two major sources and is admixed depending on the geographic area. These sources are biogenic detritus and anthropogenic emissions. The biogenic materials in the solvent-extractable organic matter are comprised predominantly of higher plant waxes, with lesser amounts of resin and microbial detritus and the anthropogenic components are primarily vehicular emissions (e.g. oils, soot, etc.) and input from combustion (e.g. charcoal, thermally-altered biogenic matter, etc.). Both biogenic detritus and anthropogenic emissions contain organic compounds (C12−C40+), which can be identified with unique and distinguishable distribution patterns. Molecular composition analysis has been applied to such extracts after suitable chemical separation into subfractions (i.e. hydrocarbons, ketones, aldehydes, carboxylic acids, alcohols, and wax esters). Both homologous compound series and specific natural products (e.g. phytosterols, terpenes, etc.) are identified as molecular markers. Aerosols from rural and remote areas in the western United States, South America, Nigeria and Australia have been analyzed and all contained predominantly plant waxes. The loadings of hydrocarbons ranged approximately from 10–1400 ng/m3 of air, of fatty acids from 10–450 ng/m3 and of fatty alcohols from 10–1650 ng/m3. These higher molecular weight lipids primarily from flora comprise a major component of the organic carbon in rural and remote aerosols. They are thus important indicators for regional biogenic sources in the global cycling of organic carbon.

Fourier transform infrared kinetic studies of the reaction of HONO with HNO3, NO3 and N2O5 at 295 K

Abstract: The kinetics of the reaction of nitrous acid (HONO) with nitric acid (HNO3), nitrate radicals (NO3) and dinitrogen pentoxide (N2O5) have been studied using Fourier transform infrared spectroscopy. Experiments were performed at 700 torr total pressure using synthetic air or argon as diluents. From the observed decay of HONO in the presence of HNO3 a rate constant of k<7×10-19 cm3 molecule-1 s-1 was derived for the reaction of HONO with HNO3. From the observed decay of HONO in the presence of mixtures of N2O5 and NO2 we have also derived upper limits for the rate constants of the reactions of HONO with NO3 and N2O5 of 2×10-15 and 7×10-19 cm3 molecule-1 s-1, respectively. These results are discussed with respect to previous studies and to the atmospheric chemistry of HONO.

A photoelectric detector for the measurement of photolysis frequencies of ozone and other atmospheric molecules

Abstract: Photoelectric detectors for the measurement of photolysis frequencies of different trace gases in the atmosphere are described. They exhibit uniform response characteristics over one hemisphere (2π sr) and wavelength characteristics closely matched to those of the photolysis frequencies J O1D, J NO2, and J NO3, respectively. Absolute calibration of the J O1D detector was performed by chemical actinometry with an accuracy of ±16 percent. Simultaneous measurements of J NO2 and J O1D are presented.

Anthropogenic aerosols and gases in the lower troposphere at Alert Canada in April 1986

Abstract: During April 1986, as part of an international arctic air chemistry study (AGASP-2), ground level observations of aerosol trace elements, oxides of sulphur and nitrogen and particle number size distribution were made at Alert Canada (82.5N, 62.3W). Pollution haze was evident as indicated by daily aerosol number (size > 0.15 μm diameter) and SO4 = concentrations in the range 125 – 260 cm−3 and 1.6 – 4.5 μg m−3, respectively. Haze and associated acidic gases tended to increase throughout the period. SO2 and peroxyacetylnitrate (PAN) mixing ratios were in the range 140 – 480 and 370 – 590 ppt(v), respectively. About 88% of the total end-product nitrogen was in the form of PAN. In air dried to 2% relative humidity by warming to room temperature, the aerosol mass size distribution had a major mode at 0.3 μm diameter and a minor one at 2.5 μm. Aerosol mass below 1.5 μm was well correlated with SO4 =, K+ and PAN. There was a steady increase in the oxidized fraction of total airborne sulphur and nitrogen oxide throughout April as the sun rose above the horizon and remained above. The mean oxidation rate of SO2 between Eurasia and Alert was estimated as 0.25 – 0.5% h−1. The molar ratio of total nitrogen oxide to total sulphur oxide in the arctic atmosphere (0.67±0.17) was comparable to that in European emissions. A remarkably strong inverse correlation of filterable Br and O3 led to the conclusion that O3 destruction and filterable Br production below the Arctic surface radiation inversion is associated with tropospheric photochemical reactions involving naturally occurring gaseous bromine compounds.

Alkyl nitrate formation from the atmospheric photoxidation of alkanes; a revised estimation method

Abstract: The available experimental data concerning the yields of alkyl nitrates in the reactions of alkyl peroxy radicals with NO have been used to derive a revised expression for the estimation of alkyl nitrate yields in the atmospheric photooxidation of alkanes as a function of temperature and pressure. This revised expression gives more reasonable predictions of alkyl nitrate yields under high altitude tropospheric conditions than that which has been previously published.

Measurements of formaldehyde in the troposphere by tunable diode laser absorption spectroscopy

Abstract: Measurements of formaldehyde, HCHO, using tunable diode laser abssrption spectroscopy (TDLAS) are reported for four sites in North America. The TDLAS apparatus and its application to these measurements is described. Detection limits of ca. 0.25 ppbv were obtained with a three-minute time resolution. Two distinct types of diurnal behaviour were observed: in the absence of local pollution sources the HCHO diurnal variation was weak and HCHO is not lost during the night. We conclude that the lifetime of HCHO with respect to dry deposition was greater than 50 h at the least-polluted site. At sites downwind of pollution sources, the HCHO peaks near noon and declines in the afternoon. At the least-polluted location, the most probable value for HCHO was 0.25–0.5 ppbv, while hourly averaged values up to 12 ppbv were observed at the other locations.

Studies of ice nucleation by Arctic aerosol on AGASP-II

Abstract: Aerosol particles were collected on filters for studies of their ability to nucleate ice during the second Arctic Gas and Aerosol Sampling Program (AGASP-II) in April, 1986. The ice nuclei (IN) samples were collected from an aircraft at altitudes ranging from the surface to the vicinity of the tropopause in Arctic locations over Alaska, northern Canada and Greenland. Samples of other components of the aerosol were collected and measurements were made of other properties of the aerosol coincident in time with the IN samples. The IN filters were exposed to water saturation in a dynamic developing chamber at −15° C and −25° C. Ice crystals grew on the IN and were counted on the filters at discrete time intervals during the exposure period to determine the rate of ice nucleation and the final concentration of (IN). Results show that Arctic haze aerosol, identified by pollutant signatures, had lower IN concentrations, a lower IN to total aerosol fraction and slower ice nucleation rates than aerosol which had a chemical signature more indicative of the remote unpolluted troposphere. These observations suggest that the Arctic haze aerosol does not efficiently form ice in the arctic troposphere. This may be a factor contributing to the long-range transport of Arctic haze.

The solubility of SO2 and the dissociation of H2SO3 in NaCl solutions

Abstract: The pK 1 * and pK 2 * of H2SO3 have been determined in NaCl solutions as a function of ionic strength (0.1 to 6 m) and temperature (5 and 25 °C). The extrapolated values in water were found to be in good agreement with literature data. The experimental results have been used to determine the Pitzer interaction parameters for SO2, HSO 3 - and SO 3 - in NaCl solutions. The resultant parameters for NaHSO3 and Na2SO3 were found to be in reasonable agreement with the values for NaHSO4 and Na2SO4. It, thus, seems reasonable to assume that the interactions of Mg2+ and Ca2+ with HSO 3 - and SO 3 - can be estimated from the values with HSO 4 - and SO 4 - until experimental values are available. Measurements of pK 1 * and pK 2 * in artificial seawater were found to be in good agreement with the calculated values using the derived Pitzer parameters. It is, thus, possible to make reasonable estimates of the activity coefficients of HSO 3 - and SO 3 - ions and pK 1 * and pK 2 * for the ionization of H2SO3 in marine aerosols.

Spectroscopic measurements of atmospheric carbon monoxide and methane. 1: latitudinal distribution

Abstract: The results of spectroscopic total column measurements of CO and CH4 at different points of the Northern and Southern Hemispheres in 1970–1985, are reported. Seasonal cycles of CO are evident for all the sites. The Northern Hemispheric long-term positive trend of CO seems to be 1.5–2% per year. In the Southern Hemisphere, temporal increasing was not detected and a possible upper limit for it is about 0.6% per year. Methane concentration in the Northern Hemisphere increases at a rate of 1.2% per year.

Correlations among combustion effluent species at Barrow, Alaska: Aerosol black carbon, carbon dioxide, and methane

Abstract: As part of the second Arctic Gas and Aerosol Sampling Program (AGASP II) continuous measurements of atmospheric aerosol black carbon (BC) were made at the NOAA/GMCC observatory at Barrow, Alaska (71°19′N, 156°36′W) during the period March 21–April 22, 1986. Black carbon is produced only by incomplete combustion of carbonaceous materials and so is a particularly useful atmospheric indicator of anthropogenic activities. The BC data have been analyzed together with the concurrent measurements of carbon dioxide (CO2), methane (CH4), and condensation nuclei (CN) that are routinely made at the observatory. All four species showed elevated and highly variable concentrations due to local human activities, principally in the township of Barrow, 7 km to the southwest, and at the DEW Line radar installation 1 km to the northwest. We distinguish between those periods of the record that are affected by local activities and those that are not, on the basis of the short-term (periods of up to 1 hour) variability of the continuous CO2 and CN records, with large short-term variabilities indicating local sources. We identified seven periods of time (events) with durations ranging from 13 to 37 hours when the BC, CO2, and CH4 concentrations changed smoothly over time, were highly correlated with each other, and were not influenced by local activities. These events had BC/CO2 ratios in the range (50–103)×10−6. These ratios are dimensionless since we convert the CO2 concentrations to units of ng m−3 of carbon. Such values of BC/CO2 are characteristic of the combustion effluent from large installations burning heavy fuel oil or coal, automobiles, and domestic-scale natural gas usage. We conclude that these events are indicative of air masses that have been polluted with combustion emissions in a distant location and then transported to the Arctic. In the absence of species-selective loss mechanisms, these air masses will maintain their combustion effluent signatures during the transport. The BC/CO2 ratios found for the local combustion activities are consistent with those expected from known combustion processes.

Arctic hazes in summer over Greenland and the North American Arctic. I: Incidence and origins

Abstract: Airborne observations during August 1985 over Greenland and the North American Arctic revealed that dense, discrete haze layers were common above 850 mb. No such hazes were found near the surface in areas remote from local sources of particles. The haze layers aloft were characterized by large light-scattering coefficients due to dry particles (maximum value 1.24 × 10−4m−1) and relatively high total particle concentrations (maximum value 3100 cm−3). Sulfate was the dominant ionic component of the aerosol (0.06 – 1.9 μg m−3); carbon soot was also present. Evidence for relatively fresh aerosols, accompanied by NO2 and O3 depletion, was found near, but not within, the haze layers. The hazes probably derived from anthropogenic sources and/or biomass burning at midlatitudes.

Airborne and lidar measurements of aerosol and cloud particles in the troposphere over Alert, Canada in April 1986

Abstract: As a component of the Canadian Arctic Haze Study, held coincident with the second Arctic Gas and Aerosol Sampling Program (AGASP II), vertical profiles of aerosol size distribution (≥0.17 μm), light scattering parameters and cloud particle concentrations were obtained with an instrumented aircraft and ground-based lidar system during April 1986 at Alert. Northwest Territories. Average aerosol number concentrations range from about 200 cm−3 over the Arctic ice cap to about 100 cm−3 at 6 km. The aerosol size spectrum is virtually free of giant or coarse aerosol particles, and does not vary significantly with altitude. Most of the aerosol volume is concentrated in the 0.17–0.50 μm size range, and the aerosol number concentration is found to be a good surrogate for the SO4 = concentration of the Arctic haze aerosol. Comparison of the aircraft and lidar data show that, when iced crystal scattering is excluded, the aerosol light scattering coefficient and the lidar backscattering coefficient are proportional to the Arctic haze aerosol concentration. Ratios of scattering to backscattering, scattering to aerosol number concentration, and backscattering to aerosol number concentration are 15.3 steradians, 1.1×10−13 m2, and 4.8×10−15 m2 sr−1, respectively. Aerosol scattering coefficients calculated from the measured size distributions using Mie scattering agree well with measured values. The calculations indicate the aerosol absorption optical depth over 6 km to range between 0.011 and 0.018. The presence of small numbers of ice crystals (10–20 crystals 1−1 measured) increased light scattering by over a factor of ten.

Nitrate in the atmospheric boundary layer of the tropical South Pacific - Implications regarding sources and transport

Abstract: Weekly bulk aerosol samples collected at three sites in the tropical South Pacific from 1983 to 1987 are analyzed. The mean nitrate concentrations obtained for the sites range from 0.107 to 0.117 microg/cu m. The results suggest that the region is minimally affected by the transport of soil material and pollutants from the continents. Measurements from sites in the tropical North Pacific show mean nitrate concentrations that are about three times higher than those in the South Pacific, showing that the North Pacific is significantly impacted by the transport of material from Asia and North America. The relationships between the nitrate concentrations to other constituents at American Samoa are discussed, including nonseasalt sulfate, Pb-210, and Be-7.

Carbon dioxide and methane in the Arctic atmosphere

Abstract: Fifty flask air samples were taken during April 1986 from a NOAA WP-3D Orion aircraft which flew missions across a broad region of the Arctic as part of the second Arctic Gas and Aerosol Sampling Program (AGASP II). The samples were subsequently analyzed for both carbon dioxide (CO2) and methane (CH4). The samples were taken in well-defined layers of Arctic haze, in the background troposphere where no haze was detected, and from near the surface to the lower stratosphere. Vertical profiles were specifically measured in the vicinity of Barrow, Alaska to enable comparisons with routine surface measurements made at the NOAA/GMCC observatory. Elevated levels of both methane and carbon dioxide were found in haze layers. For samples taken in the background troposphere we found negative vertical gradients (lower concentrations aloft) for both gases. For the entire data set (including samples collected in the haze layers) we found a strong positive correlation between the methane and carbon dioxide concentrations, with a linear regression slope of 17.5 ppb CH4/ppm CO2, a standard error of 0.6, and a correlation coefficient (r2) of 0.95. This correlation between the two gases seen in the aircraft samples was corroborated by in situ surface measurements of these gases made at the Barrow observatory during March and April 1986. We also find a similar relationship between methane and carbon dioxide measured concurrenty for a short period in the moderately polluted urban atmosphere of Boulder, Colorado. We suggest that the strong correlation between methane and carbon dioxide concentrations reflects a common source region for both, with subsequent long-range transport of the polluted air to the Arctic.

N2O measurements of air extracted from antarctic ice cores: Implication on atmospheric N2O back to the last glacial-interglacial transition

Abstract: A method has been developed for determining the N2O concentrations of air bubbles trapped in ice cores. The air is removed by cutting ice samples of about 45 cm3 with a rotating knife, under pure nitrogen. About 2 cm3 of the gas extracted from the ice is analyzed. The N2O concentrations are measured by gas chromatography, using electron capture detection with a detection limit of approximately 1 ppbv. The accuracy of the analysis is lower than 6%. This method has been used to analyze 34 Antarctic ice samples. Twelve air samples are from the D57 core and date approximately from AD 1600 and 1900. Data indicate a concentration of about 270 ppbv approximately 400 years ago, and of about 293 ppbv for the beginning of the 20th Century. The other samples have been taken from the Dome C core and date back to the time period extending from the Holocene to the Last Glacial Maximum. The results obtained for the Holocene period are in very good agreement with the concentrations measured for the pre-industrial time from the D57 core and indicate that, during the Holocene period, atmospheric N2O mixing ratios may have remained fairly constant. The value observed during the last climatic transition suggest a slight increase in the N2O concentrations when the climate was warming up. The results obtained on samples formed during the Last Glacial Maximum show high scattering which is best explained by the bad quality of this part of the core.

The effect of nitrogen fertilization on the COS and CS2 emissions from temperature forest soils

Abstract: The net fluxes of carbonyl sulfide (COS) and carbon disulfide (CS2) to the atmosphere from nitrogen amended and unamended deciduous and coniferous forest soils were measured during the spring of 1986. We found that emissions of these gases from acidic forest soils were substantially increased after nitrogen fertilization. The total (COS+CS2) emissions were increased by nearly a factor of three in the hardwood stand and were more than doubled in the pine stand. Furthermore, vegetation type appeared to have an influence on which was the dominant sulfur gas released from the forest soils. The added nitrogen caused a dramatic increase in COS emissions from the hardwood stand (a factor of three increase), while CS2 emissions from this site were not affected. We observed the opposite response in the pine stand; that is, the nitrogen fertilization had no affect on COS emissions, but did stimulate CS2 emissions (a factor of more than nine increase).

The effects of the Arctic haze as determined from airborne radiometric measurements during AGASP II

Abstract: The effect of the Arctic-haze aerosol on the parameters of solar radiation was investigated using airborne radiometric measurements of radiation parameters during the second Arctic Gas and Aerosol Sampling Project. Simultaneously with absorption measurements, optical depths and total, direct, and scattered radiation fields were determined. The experimentally determined parameters were used to define an aerosol model, which was then used to calculate atmospheric heating rate profiles. It was found that, besides the increased absorption (30 to 40 percent) and scattering of radiation by the atmosphere, Arctic haze reduces the surface absorption of solar energy by 6 to 10 percent, and the effective planetary albedo over ice surfaces by 3 to 6 percent.

Spectroscopic measurements of atmospheric carbon monoxide and methane. 2: Seasonal variations and long-term trends

Abstract: A spectroscopic technique for measuring CO and CH4 contents is described and the latitudinal distributions of these gases are presented. Carbon monoxide abundance decreases southward, having two local maxima: in midlatitudes and in the tropics. The slope of latitude dependence varies according to the season of the year. The difference in CH4 content does not exceed the accuracy of the method (±8%).

Meteorology and haze structure during AGASP-II, Part 1: Alaskan Arctic flights, 2–10 April 1986

Abstract: The second Arctic Gas and Aerosol Sampling Program (AGASP-II) was conducted across the Alaskan and Canadian Arctic in April 1986, to study the in situ aerosol, and the chemical and optical properties of Arctic haze. The NOAA WP-3D aircraft, with special instrumentation added, made six flights during AGASP-II. Measurements of wind, pressure, temperature, ozone, water vapor, condensation nuclei (CN) concentration, and aerosol scattering extinction (bsp) were used to determine the location of significant haze layers. The measurements made on the first three flights, over the Arctic Ocean north of Barrow and over the Beaufort Sea north of Barter Island, Alaska are discussed in detail in this report of the first phase of AGASP II. In the Alaskan Arctic the WP-3D detected a large and persistent region of haze between 960 and 750 mb, in a thermally stable layer, on 2, 8, and 9 April 1986. At its most dense, the haze contained CN concentrations >10,000 cm−3 and bsp of 80×10−6 m−1 suggesting active SO2 to H2SO4 gas-to-particle conversion. Calculations based upon observed SO2 concentrations and ambient relative humidities suggest that 104–105 small H2SO4 droplets could have been produced in the haze layers. High concentrations of sub-micron H2SO4 droplets were collected in haze. Ozone concentrations were 5–10 ppb higher in the haze layers than in the surrounding troposphere. Outside the regions of haze, CN concentrations ranged from 100 to 400 cm−3 and bsp values were about (20–40)×10−6 m−1. Air mass trajectories were computed to depict the air flow upwind of regions in which haze was observed. In two cases the back trajectories and ground measurements suggested the source to be in central Europe.

7Be deposition in a high-rainfall area of New Zealand

Abstract: Concentrations of natural 7Be in air and rainwater were monitored for one year at Hokitika, New Zealand. The mean airborne concentration was 3.1±1.3 mBq m−3, the mean Hokitika, New Zealand. The mean airborne concentration was 3.1±1.3 mBq m−3, the mean concentration in rainwater was 2600±1200 Bq m−3, and the mean total deposition was estimated to be 130±99 Bq m−2 wk−1. Most of the 7Be was wet deposited and the washout ratio was independent of precipitation amount. A significant linear relationship exists between the weekly wet deposition flux and weekly precipitation at this high-rainfall site.

Pan over the Arctic; Observations during AGASP-2 in April 1986

Abstract: During three of the flights with the NOAA P3 Orion over the Arctic icecap in April 1986, the atmospheric concentration of PAN (peroxyacetyl nitrate) was measured. Due to major experimental problems, the uncertainty in the data is large (+/−50%), but, nevertheless, some important trends can be resolved. More than 600 (+/−300) ppt(v) of PAN was present in a moderately dense arctic haze layer, confirming conclusions reached from surface observations at Alert, N.W.T., Canada, that PAN is a major odd nitrogen species in Arctic polluted air masses. In relatively clean air off Barrow, Alaska, PAN levels were well below 100 (+/−50) ppt(v), increasing with altitude, in agreement with theoretical predictions concerning the occurrence of PAN in clean air. PAN mixing ratios in the upper troposphere or lower stratosphere were variable (from ca. 30 (+/−15) ppt(v) on April 13 up to 140 (+/−70) ppt(v) on April 8), suggesting involvement in the tropospheric-stratospheric exchange of odd nitrogen. To place the PAN data in a broader context, measurements of other NOy compounds as well as integrated SOx data are also reported.

Aerosol black carbon measurements in the Arctic haze during AGASP-II

Abstract: During the second Arctic Gas and Aerosol Sampling Program conducted in April 1986, we performed measurements of the optically absorbing carbonaceous component of the ambient aerosol from the NOAA WP-3D aircraft operating between sea level and 10 km altitude. We collected the aerosol of filters that were exposed for several hours; we also operated the aethalometer to measure the concentration of aerosol black carbon in real time. The filter analyses represent averages over the altitude range and time span during which the filter was collecting. The real-time results were sorted by altitude to calculate vertical profiles of black carbon concentration. Values typically ranged from 300 to 500 ng m−3 at lower altitudes, decreasing gradually to 25 to 100 ng m−3 at 8–10 km. Strong stratification at lower altitudes was frequently observed. The magnitude of these concentrations suggests that the sources are distant regions of considerable fuel consumption. The presence of this material in the tropospheric column and its probable deposition to the high-albedo surface may result in perturbations of the solar radiation balance. The concentrations measured at the highest altitudes may mean that particulate carbon and accompanying emissions for which it is a tracer are mixing into the stratosphere.

Ultraviolet absorption spectrum of trifluoro-bromo-methane, difluoro-dibromo-methane and difluoro-bromo-chloro-methane in the vapor phase

Abstract: Ultraviolet absorption cross-sections of trifluoro-bromo-methane (CF3Br-Halon 1301), difluoro-dibromo-methane (CF2Br2-Halon 1202) and of difluoro-bromo-chloro-methane (CF2BrCl-Halon 1211) are measured in the wavelength interval 172–304 nm for temperatures ranging from 210 to 295 K with uncertainties of between 2 and 4%. They are compared with previous measurements available at room temperature. Temperature effects are discussed and parametrical formulae are proposed to compute the absorption cross-sections for wavelengths and temperatures useful in atmospheric modelling calculations. Photodissociation coefficients are presented and their temperature dependence is discussed.

Kinetics of the reactions of hydroxyl radicals with aliphatic ethers studied under simulated atmospheric conditions

Abstract: Rate coefficients have been measured for the reactions of hydroxyl radicals with a range of aliphatic ethers by a competitive technique. Mixtures of synthetic air containing a few ppm of nitrous acid, isobutene and an ether were photolyzed in a Teflon-bag smog chamber. From the rates of depletion of the ether and of the isobutene, and based on the value of the rate coefficient k(OH+i-C4H8)=5.26×10-11 cm3 molecule-1 s-1, the following rate coefficients were obtained for the hydroxyl radical reactions at 750 Torr and at 294±2K in units of 10-12 cm3 molecule-1 s-1: diethylether = 12.0±1.1, di-n-propylether = 15.3±1.6, di-n-butylether=17.1±0.9, ethyl n-butylether = 13.5±0.4, ethyl t-butyl-ether = 5.6±0.5, and di-isobutylether = 26.1±1.6. The quoted error limits correspond to 2 standard deviations but do not include any contribution from k(OH+i-C4H8) for which the error limits are estimated to be about ±10%. The results are discussed in relation to the available literature data and considered in terms of the structure-activity relation for hydroxyl radical reactions with organic molecules.

Elemental composition of particulate material sampled from the Arctic haze aerosol

Abstract: Thirty-six aerosol filter samples collected in tropospheric Arctic haze layers, in the stratosphere, and in the marine boundary layer during the 1983 Arctic Gas and Aerosol Sampling Program were analyzed for trace elements using instrumental neutron activation analysis. Average crustal dust concentrations were 540 ng/m3 and 330 ng/m3 for samples collected in Arctic haze over the North American and Norwegian Arctic, respectively. An average marine salt concentration of 120 ng/m3 was obtained for haze samples collected above the marine boundary layer on both sides of the Arctic.

NOAA WP-3D instrumentation and flight operations on AGASP-II

Abstract: One component of the second Arctic Gas and Aerosol Sampling Program conducted in March and April 1986 was supported with an instrumented NOAA WP-3D atmospheric research aircraft, which was used to conduct measurements of wind, temperature, ozone, water vapor, the concentration of condensation nuclei, and aerosol scattering extinction coefficient in order to determine the locations and properties of haze layers. The WP-3D flights consisted of three missions north of Alaska and three in the Canadian Arctic near Alert. This paper describes the NOAA WP-3D aircraft; the meteorological, gas, and aerosol sampling systems utilized; and the flight operations of the six WP-3D flights.

Observations of nitric oxide fluxes over grass

Abstract: Eddy correlation measurements of NO vertical flux were made periodically from October 1983 through June 1984 at a height of eight meters above grass in northeastern Illinois, U.S.A. From 207 data points, each representing a 25 min average, 19 daytime cases and 8 nighttime cases were selected on the basis of steady, nonadvective atmospheric conditions. Each case was represented by a set of data constituting a 3 to 5 hr average. Concentrations of O3, NO, and NO y (from which NO2 was inferred) and local atmospheric and surface conditions also were measured, to provide the information necessary to assess the relative importance of surface deposition, surface emission, and air chemistry on the observed NO flux. On the basis of a linear regression analysis applied with independent variables representing physical, chemical, and biological processes, surface uptake of NO was very small for data primarily collected in the daytime during spring, and measured deposition velocities at a height of 8 m were very small, much smaller than expected for NO2. For the same time period, the surface emission rates of elemental nitrogen in NO were in the range of 1.4 to 4.2 ng m-2 s-1 for moist, unsaturated soils at temperatures near 15° C. These emissions were partially masked in the measured fluxes by rapid in-air chemical reactions involving O3 and NO2. The effects of rapid in-air chemical reactions involving O3 were to decrease the (upward) flux of NO with height. While the information collected at night was too limited to strongly support hypotheses concerning emissions and deposition, a pathway for NO production by reactions involving NO3 and related compounds was indicated. For daytime conditions, this production pathway is not evident, probably because of the relatively strong effects of photochemical reactions involving NO, NO2, and O3.

Gas phase reactions of alkyl nitrates with hydroxyl radicals under tropospheric conditions in comparison with photolysis

Abstract: Rate constants for the reaction of OH radicals with some branched alkyl nitrates have been measured applying a competitive technique. Methyl nitrite photolysis in synthetic air was used as OH radical source at 295±2 K and 1000 mbar total pressure. Using a rate constant of 2.53×10-12 cm3 s-1 for the reaction of OH radicals with n-butane as reference, the following rate constants were obtained (units: 10-12 cm3 s-1): isopropyl nitrate, 0.59±0.22; isobutyl nitrate, 1.63±0.20; 3-methyl-2-butyl nitrate, 1.95±0.15; 2-methyl-1-butyl nitrate, 2.50±0.15; 3-methyl-1-butyl nitrate, 2.55±0.35. These values have been combined with the literature data to recalculate the substituent factors F(X) for the different nitrate groups which can be used to predict OH rate constants for organic nitrates for which experimental data are not available.

A Molybdenum Oxide Annular Denuder System for Gas Phase Ambient Ammonia Measurements

Abstract: An automated molybdenum oxide annular denuder system (MOADS) has been developed for gas phase ambient ammonia measurements. This system combines high sensitivity (detection limit <50 pptv) with continuous sampling, moderate collection times (30 min) and automated operation. The present denuder design confers two important advantages over the tungsten oxide coated quartz denuder tubes used previously for nitric acid and ammonia measurements. First, the present denuders use oxidized metal substrates and are easier to fabricate and more durable than denuders made from metal oxide coated glass or quartz tubes. Second, molybdenum (VI) oxide surfaces are used which oxidize a reproducible fraction of the adsorbed NH3 directly to NO upon desorption eliminating the need for a secondary catalytic converter. Laboratory tests of the collection/recovery characteristics of annular denuders made from both the (IV) and (VI) oxides of tungsten and molybdenum are described and preliminary results from field tests are presented.