• D M Chate

      Articles written in Journal of Earth System Science

    • Atmospheric aerosol formation and its growth during the cold season in India

      D M Chate P Murugavel

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      The effects of molecular diffusivity of H2SO4 and NH3 vapours on nucleated particles of SO$^{2−}_{4}$ and NO$^{−}_{3}$ species are reported. Condensation sink and source rate of H2SO4 and NH3 vapours, growth rates and ratios of real to apparent nucleation rates are calculated for SO$^{2−}_{4}$ and NO$^{−}_{3}$ aerosols using fractional contributions of them in total aerosol size-distribution during the measurement period at Pune, reported in Chate and Pranesha (2004). The percentage of nucleated SO$^{2−}_{4}$ and NO$^{−}_{3}$ aerosols of mid-point diameter 13 nm are 2% and 3% respectively of the total particles (13 nm ≤ $D_{p}$ ≤750nm) for both H2SO4 and NH3 diffusion. In the diameter range $75 nm \leq D_{p} \leq 133 nm$, it is 48% and 45% of SO$^{2−}_{4}$ and NO$^{−}_{3}$ aerosols, respectively for NH3 diffusion and 43% and 36% of SO$^{2−}_{4}$ and NO$^{−}_{3}$ for H2SO4 diffusion. Increase in percentage of nucleated particles of these species corresponding to mid-point diameter 133 nm around 0900 h IST is significantly higher than that of mid-point diameter 13 nm and it is due to photo-chemical nucleation, coagulation and coalescence among nucleated clusters. The ratios of real to apparent formation rates for SO$^{2−}_{4}$ and NO$^{−}_{3}$ aerosols are 12% and 11% respectively, corresponding to mid-point diameter 13 nm, 17% and 13%, for midpoint diameter 133 nm and 12% and 9.5%, for mid-point diameter 750 nm. The results indicate that nucleation involving H2SO4 and acidic NH3 diffusion on SO$^{2−}_{4}$ and NO$^{−}_{3}$ particles is the most relevant mechanism in this region.

    • Chemistry of snow and lake water in Antarctic region

      Kaushar Ali Sunil Sonbawane D M Chate Devendraa Siingh P S P Rao P D Safai K B Budhavant

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      Surface snow and lake water samples were collected at different locations around Indian station at Antarctica, Maitri, during December 2004-March 2005 and December 2006-March 2007.Samples were analyzed for major chemical ions. It is found that average pH value of snow is 6.1. Average pH value of lake water with low chemical content is 6.2 and of lake water with high chemical content is 6.5.The Na+ and Cl are the most abundantly occurring ions at Antarctica. Considerable amount of SO$^{2-}_{4}$ is also found in the surface snow and the lake water which is attributed to the oxidation of DMS produced by marine phytoplankton.Neutralization of acidic components of snow is mainly done by NH$^{+}_{4}$ and Mg2+. The Mg2+, Ca2+ and K+ are nearly equally effective in neutralizing the acidic components in lake water.The NH$^{+}_{4}$ and SO$^{2-}_{4}$ occur over the Antarctica region mostly in the form of (NH4)2SO4.

    • Volatile properties of atmospheric aerosols during nucleation events at Pune, India

      P Murugavel D M Chate

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      Continuous measurements of aerosol size distributions in the mid-point diameter range 20.5–500 nm were made from October 2005 to March 2006 at Pune (18° 32′N, 73° 51′E), India using Scanning Mobility Particle Sizer (SMPS). Volatilities of atmospheric aerosols were also measured at 40°, 125°, 175°, 300° and 350°C temperatures with Thermodenuder–SMPS coupled system to determine aerosol volatile fractions. Aerosols in nucleated, CCN and accumulated modes are characterized from the measured percentage of particles volatized at 40°, 125°, 175°, 300° and 350°C temperatures. Averaged monthly aerosol concentration is at its maximum in November and gradually decreases to its minimum at the end of March. The diurnal variations of aerosol concentrations gradually decrease in the night and in early morning hours (0400–0800 hr). However, concentration attains minimum in its variations in the noon (1400–1600 hr) due to higher ventilation factor (product of mixing height and wind speed). The half an hour averaged diurnal variation of aerosol number concentration shows about 5 to 10-fold increase despite the ventilation factor at higher side before 1200 hr. This sudden increase in aerosol concentrations is linked with prevailing conditions for nucleation bursts. The measurement of volatile fraction of ambient aerosols reveals that there are large number of highly volatile particles in the Aitken mode in the morning hours and these volatile fractions of aerosols at temperatures > 150°C are of ammonium chloride and ammonium sulfate, acetic and formic acids.

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