Atmospheric Environment (1967)最新文献

Filter packs have commonly been used to sample atmospheric gases and particles. However, reactions between the gases and particles can occur, particularly during summer sampling. Recently, annular denuder systems (ADS) have been developed, consisting of denuder tubes that strip the reactive gases from the air, thus leaving the particles to be collected on the ADS filters. We compared the ADS to filter packs in the winter, when the filter packs are most reliable. The species sampled included SO₂, HNO₃, HCl and particulate NO₃⁻, SO₄²⁻, Na⁺ and Cl⁻. HNO₂ was also sampled with the ADS.

Filter packs are far less expensive than ADS and simpler to use in the field. The usual filter pack problem, dissociation of particulate NO₃⁻ to gaseous HNO₃, was not apparent during winter sampling. However, the open-faced filter packs are more exposed to the elements than the ADS, thus leading to high and variable blank levels—particularly for NaCl where blank levels averaged 40% of measured concentrations. In addition, up to 50% of the SO₂ was collected on the backup collector, indicating occasional poor collection efficiency. In contrast, the ADS had low blanks and high collection efficiencies with less than 3% of the SO₂ on the backup collector.

Measurements between filter packs and the ADS agreed within 10% for particles and hydrochloric acid. However, due to losses of HNO₃ in the filter pack and small losses of particles in the denuder sections, HNO₃ concentrations appear greater with the ADS than with filter packs. To the extent that the particle loss in the ADS is due to bounce-off from the impactor frit, it can be corrected in future studies. Sulfur dioxide is also 14% greater with the ADS than with the filter pack and reasons for the difference are considered.

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.

During the STRATOZ III experiment (June 1984) designed for a study of trace gases in the atmosphere, more than 2000 concurrent measurements of CO and CH₄ by gas chromatography were obtained from a series of flights aboard a scientific aircraft “Caravelle 116” between 70°N and 60°S, and up to a cruising altitude of 12 km, over the Atlantic Ocean and along the American, African and European continents.

While a global interpretation of the data must await the examination of the whole series of compounds measured, a preliminary analysis of the results obtained for CO and CH₄ is reported here.

The CO and CH₄ mixing ratios are found to be higher in the Northern Hemisphere than in the Southern, which reflects the meridional distribution of their sources and the influence of tropospheric photochemistry. A prominent CO difference between the two hemispheres is observed in the continental air (NH: 100–200 ppb; SH: 80–90 ppb) while the oceanic air is much more homogeneous (NH: 80–90 ppb; SH: 60–70 ppb). In the case of CH₄, a regular decrease is observed between the high latitudes of the Northern Hemisphere and those of the Southern.

For the Southern Hemisphere, the CO values are in agreement with literature data, but for the Northern they are lower than previously reported. The CH₄ results suggest the possible existence of natural sources in the Southern Hemisphere (Amazonia; South Pacific).

A comparison of the measurements made in the Southern Hemisphere with reliable data sets previously reported in the literature confirms an increase rate of 1.2 ± 0.3 % per year for CH₄, but does not provide any evidence for a long term variation of the CO content.

The comprehensive data reported here will be of valuable interest to improve the understanding of the physico-chemistry of the troposphere and its evolution.