Atmospheric Environment (1967)最新文献

From late February to mid April 1985 pressurized air samples were collected 3 times per week on weathership M in the North Atlantic and in Ny-Ålesund on Svalbard. The samples were analyzed for individual light hydrocarbons C₂-C₆, and it was found that the average sum of C₂-C₆ hydrocarbons was about 35 ppbC in Ny-Ålesund and 31 ppbC on ship M, with the least reactive species ethane and propane as the most abundant ones.

Research on Arctic haze has provided an example when anticyclones may play a dominant role in carrying out low-level tropospheric long-range transport. This dominant role of anticyclones in transporting Arctic haze may be the result of the unique geographic and climatological situation existing during winter/spring in which both the huge Eurasian continent and the adjacent ice-covered Arctic Ocean tend to be regions where anticyclones form and exist over long periods of the winter and spring seasons. It is assumed that the seasonal variation of transport mechanisms provided by anticyclones is the primary cause for the seasonal variation of Arctic haze. Centers of anticyclones are the regions where air masses form and obtain their characteristics, both meteorological and chemical, due to the aerosols and gases released into the air. Transport within an air flow along the edges of quasi-stationary anticyclones will remain under stable atmospheric conditions, hence, dilution, lifting and removal of aerosols and gases will be less compared to a transport within the influence of a cyclonic pressure system. According to the concept of isentropic flow, anticyclones may dominate only low-level transport, whereas cyclones may be more important in controlling transport at upper tropospheric levels.

Samples from three snowpits near Dye 3 in South Greenland have been used to study seasonal variations in contaminant transport from the atmosphere to the Ice Sheet. The snowpits cover the years 1982–1987. The samples have been dated by comparing δ¹⁸O values with meteorological data from Dye 3. Airborne concentrations of SO²⁻₄ over the Ice Sheet have been estimated for the dates corresponding to each snowpit sample by statistically analyzing data from several air monitoring stations throughout the Arctic, and computing average values from the appropriate stations. Seasonal variations in concentrations in air, concentrations in snow, and mass-basis scavenging ratios (concentration in snow divided by concentration in air) have been identified. Results indicate that concentrations of SO²⁻₄in the air show a strong peak in late February, resulting from long-range transport of mid-latitude anthropogenic emissions, while those in the snow show a broad peak in January, February and March with smaller seasonal variation overall. The smaller variation in the snow is attributed in part to the effect of riming, which results in more efficient scavenging during warm weather when airborne concentrations are low. The importance of riming is also supported by the annual cycle in scavenging ratio which peaks in mid-summer coincident with maximum temperatures. In agreement with previous estimates, dry deposition appears to account for 10–30% of the total SO²⁻₄ in the snow. Concentrations of NO⁻₃ in the snow show a strong peak in summer; natural material from the stratosphere as well as anthropogenic emissions transported from the mid-latitudes may be responsible. Concentrations of Cl⁻ in the snow are maximum in January, with relatively high concentrations during October through March and a smaller peak in July. The winter peak is believed to reflect long-range transport (LRT) of marine aerosol from north Atlantic storms, while the summer peak is attributed to seaspray from nearby coastal Greenland. Riming also may influence the seasonal variations in NO⁻₃ and Cl⁻ in the snow.

Vertical profile measurements of aerosol number density remotely in the lower atmosphere during night-time using a bistatic, continuous wave Argon ion laser radar (lidar) system have been in progress at the Indian Institute of Tropical Meteorology, Pune, India since September 1986. The observational programme includes the measurement of a minimum two and maximum seven vertical profiles of atmospheric aerosols in each month. This paper deals with the results of the analysis of lidar aerosol data archived for a period of one year (October 1986–September 1987) and presents the monthly variations in the height distribution of aerosol number density along with their deviations from the annual mean distribution. Also, presented in this paper are the results of (i) the temporal changes in the aerosol concentration at 30 m AGL and its relationship with surface wind and relative humidity, and (ii) the comparison of the aerosol profiles on some selected days with the near-simultaneously obtained vertical profiles of wind, temperature and relative humidity. The results suggest that variations of aerosol concentration exhibit a certain relationship with those of meteorological parameters, and the atmospheric stability conditions associate with the vertical gradients of concentration at the top of the aerosol layer.

A method is developed for recursive prediction of emissions and concentrations at various positions, which obey an atmospheric dispersion model, yet have a least squares deviation from observations at the same points. As a by-product, the technique yields a concentration distribution grid on each time-step. This robust procedure rationalizes data which are in dispute, and makes optimal use of incomplete source or receptor observation records. Thus several unknown source-rates may be estimated on-line as the procedure steps through the remaining observation records. An accurate advection-diffusion solution is formulated as a linear transformation for each time-step, using a sub-grid adaptation of the pseudospectral method. This is extended to the vertical dimension using the zeroth, first and second vertical moments of concentration, allowing only uniform wind profiles, but gradual wind-field and diffusivity variations in the horizontal. A discrete Kaiman filter then provides optimal estimates of all source rates, constituting the state vector, to minimize deviations from any source and receptor observations. The algorithm has been applied in a 90 km × 90 km region of the Eastern Transvaal Highveld, including nine SO₂ sources and eight detectors. Indications are that the method will be a valuable aid in interpreting such data sets.

The variability in performance of two brands of wet/dry atmospheric deposition samplers was compared for 1 year at a single site. A total of nine samplers was used. Samples were collected weekly and analyzed for pH, specific conductance, common chemical constituents and sample mass. The non-normal distribution within the data set and the non-normal distribution of residuals necessitated the application of the non-parametric Friedman test to assess the comparability of sample chemical composition and volume between and within brands of samplers. Statistically significant differences existed for most comparisons however, the test does not permit quantification of their magnitudes, except in general terms. Differences in analyzed concentrations between samplers were small.

In order to study carbonyl sulfide sources and sinks at ground level, two experiments were conducted in 1986 during temperature inversion events. In the first experiment, the samples were collected in a coastal area during land-breeze events. In the second experiment, COS vertical profiles were carried out in an agricultural area, within and above an inversion layer near the ground. Both stable atmospheric situations resulted in a deficit of COS near the ground which is attributed to the existence of a sink of COS at this level. Deposition onto vegetation seems to be the most likely mechanism for this COS uptake, a conclusion in agreement with the results of laboratory and soil flux chambers experiments.