K.G. Vohra

An experimental study of the role of radon and its daughter products in the conversion of sulphur dioxide into aerosol particles in the atmosphere

Abstract A set of experiments carried out to study the possible role of radon (Rn) and its daughters in the conversion of gaseous sulphur dioxide into particulate sulphate in the atmosphere is described. The experiments were performed under simulated atmospheric conditions in a reaction vessel containing known quantities of SO2, O2 and C2H4 in varying concentrations. The introduction of Rn gas of concentrations in the ranges prevalent in the atmosphere resulted in an enhancement of particle generation in the vessel. An increase of Rn concentration from 100 to 500 pCi m−3 resulted in an increase in the aerosol concentration in the reaction vessel from 6 × 104 to 1.4 × 10 5 cm −3 . Since the concentrations of Rn used for these experiments correspond to the average levels of Rn at ground level it can be expected that a significant fraction of the gas to particle formation could be influenced by the background concentrations of Rn. This observation has significant implications in the study of atmospheric aerosol formation mechanisms.

Lead, cadmium, zinc, copper and iron in the atmosphere of Greater Bombay

Abstract Air concentrations of Pb, Cd, Zn, Cu and Fe have been measured at eight locations in Greater Bombay. Airborne Pb concentration in the city area showed a significant correlation with the vehicular traffic density at the time of sampling. The particle size distribution of Pb aerosol has been studied at two selected locations, in the city of Bombay and a nearby hill station Matheran.

The concentrations of benzo(a)pyrene in Bombay

Abstract The concentrations of the environmental carcinogen benzo(a)pyrene in the atmospheric air of Bombay have been measured. Thin layer Chromatographic plates of silica gel C were used for the separation of sample extracts and spectrophotofluorometer was used for estimation using excitation wavelengths of 300 and 381 nm and emission wavelength of 410 nm for B(a)P. The concentrations of B(a)P in various zones in Bombay are discussed and compared with similar data from other countries. Preliminary data on the size distribution of aerosols containing B(a)P is also presented.

Bromine to lead ratios in suspended air particulate matter in Greater Bombay

Abstract Measured ratios of Br/Pb in suspended air particulates at different locations in Greater Bombay are presented. Concentrations of Br and Pb were determined by non-destructive neutron activation analysis and by anodic stripping voltammetry, respectively. The Br/Pb ratio varied from 0.12 to 0.45 with an average of 0.25 ± 0.08, as compared to 0.39 in the antiknock fuel additive. The observed Br/Pb ratio for Bombay aerosols is in agreement with the corresponding values reported by others. The present measurements suggest that bromine loss rate is very little after the particles are deposited on the filter. The probable composition of lead aerosols is discussed.

Determination of ethylene and other reactive hydrocarbons in the atmospheric air at Trombay, Bombay by gas chromatography using a chemiluminescent detector

Abstract A gas Chromatographic method is described for the determination of reactive hydrocarbons in the atmospheric air at Trombay, Bombay. Pre-concentration of the atmospheric hydrocarbons is carried out on short U-columns of silica gel kept at dry-ice temperature. The detector is based on the measurement of light intensity due to chemiluminescent reactions between O3 and the reactive hydrocarbons in the detector and is thus selectively sensitive to reactive hydrocarbons. Data on atmospheric concentrations of these hydrocarbons at Trombay is reported.

A study of the formation of aerosols in filtered atmospheric air at Trombay, Bombay

Abstract A set of atmospheric measurements was carried out at Trombay, Bombay to study the correlation between the concentration variation of freshly formed atmospheric aerosols and the variations in the ambient concentrations of some of the atmospheric trace gases. Daily values of the aerosol concentration both in filtered and unfiltered air together with the concentrations of SO2, NO, O3 and α-activity were measured during a period of 11 months. Statistical analysis of the data shows that variation of particle concentration in the filtered air is a function of not only SO2 variation but also O3 and α-activity variations. The various parameters that are likely to be involved in the formation and the variations of small particle concentration in the atmosphere have been identified.

Behaviour of aerosols formed by clustering of molecules around gaseous ions

Abstract Behaviour of aerosols formed by the clustering of vapour molecules around negative gaseous ions has been studied using thorium-B atoms as tracer. Small negative ions of high mobility are first converted to large negative ions of low mobility by passing these through a flask containing the liquid whose vapour is to be studied, using nitrogen as carrier gas. The large ions so formed consist of clusters of molecules of the vapour. These clusters are found to be stable even after the charge is lost and behave as submicron aerosol. This aerosol, along with vapour and carrier gas, fills a neoprene reservoir. In the reservoir, the aerosol grows in size by coagulation and also probably by the diffusion of vapour molecules to the surface of the particles. Mean residence time of the aerosol particles in the neoprene reservoir at different times of growth is measured by introducing thoron gas in the reservoir and studying the change in activity due to thorium-B with time. The mean aerosol particle size at different times is estimated from the residence time in the reservoir. The aerosols investigated are the products of very early stages of nucleation by ions. The possible role of this mechanism in the formation of natural condensation nuclei is discussed.

Estimation of supersaturation attained in a condensation nucleus counter

Abstract A simple method of estimating supersaturation attained in a pressure-defined expansion-type condensation nucleus counter is presented. The method is used to investigate the maximum supersaturation reached and the threshold size for detection in a commercially available nucleus counter and a laboratory counter of spherical geometry. It is shown that there is considerable deviation from ideal reversible adiabatic behaviour generally assumed for nucleus counters. It is also shown that the Kelvin equivalent threshold size for detection of atmospheric aerosols in the commercially available counter is about 50 A in diameter. Hence the number concentration of particles smaller than 50 A measured by the counter will be underestimated.

Formation of charged particles in condensation aerosol generators used for inhalation studies.

Abstract— Formation of charged particles in a condensation aerosol generator has been studied using a charge collector and a mobility analyzer. Measurements carried out using the charge collector show that the number of charged particles increases with an increase in the particle diameter. The number of charged particles measured also depends on the thickness of the sodium chloride coating on the platinum wire used in the aerosol generator for the production of condensation nuclei. It was found that the charged particle concentration increases with decreasing coating thickness. Mobility measurements have shown that the particles are singly and doubly charged. It has been estimated that about 10% of the particles produced in the generator are charged. The mechanism of formation of charged particles in the aerosol generator has been briefly discussed.

A Study of the Attachment of Radon Daughter Atoms to Aerosol Particles

Previous studies of the attachment of radon daughter atoms to aerosol particles in the atmospheric air have given varying results, a few of which did not conform to the diffusion theory developed byLassen andRau (1960). Our studies suggest that the radiolytic aerosols formed by gas-phase reactions in the presence of ionizing radiations interfere in the studies carried out with known aerosols. Radiolytic aerosols are formed spontaneously in the system, depending on the concentrations of aerosol-forming gases in the atmospheric air. It is shown that, under experimental conditions which suppressed the formation of radiolytic aerosols, the attachment rates of Ra-A atoms to aerosol particles in the range of 0.2 to 1.0 μm in diameter agree with the diffusion theory developed byLassen andRau (1960). Such investigations of the interactions between atoms, molecules, ions, and aerosol particles are highly useful in atmospheric tracer studies.