Long-term variability of trace gases over the Indian Western Himalayan Region

The four-year continuous measurements of CO, NOx, NH₃, SO_2, and O₃ were carried at a high altitude site (32.12°N, 76.56°E at 1347 m AMSL) of the Indian Western Himalayan area to study the mixing ratios of these gases for understanding the changing trends of these trace gases over the region. Each of these trace gases showed significant daily and monthly variabilities. The highest variability was recorded in the monthly mean values of O₃ as it varied from 10 to 63 ppb during the study period. All the trace gases except CO showed maximum variability in the pre-monsoon seasons due to the strong advection and vertical circulation of air masses at the site. The seasonal mean maxima of CO were recorded during the monsoon season, while the mean maxima of NH₃ were recorded during the post-monsoon seasons. The meteorological parameters have been found to influence the mixing ratios of trace gases. The least variability in the mean seasonal mixing ratios of SO₂ during the study period indicated the constant point source of SO₂ near the site. The trajectories analysis revealed that the area receives maximum air masses from the southeast to the west directions where a number of the coal-based thermal power plants, industries, cement plants, and agricultural fields are also located. The influence of valley-to-mountain circulations was also observed at the site, resulting in the transport of pollutant-rich air masses from local and distant sources to the site. A comparison of the mixing ratios of different trace gases obtained in the present study is also made with the values reported for other high altitude stations in the world.

Global tropospheric ozone dynamics. Part I: Tropospheric ozone precursors

An overview of the tropospheric ozone changes is presented focussing mainly on the tropospheric ozone precursors. The complexity of the problem is shown through the consideration of a great number of relevant substances, like nitrogen compounds, volatile organic compounds, peroxyacetyl nitrate, hydroxyl radical, carbon monoxide, alkyl nitrates. The up-to-date knowledge on the relevant numerical modelling is presented in Part II.

Simple cryoconcentration technique for the determination of peroxyacyl and alkyl nitrates in the atmosphere

A gaseous mixture of methyl nitrate, n-propyl nitrate, peroxyacetyl nitrate and peroxypropionyl nitrate was successfully cryoconcentrated using a gas sampling valve with its loop filled with glass beads placed inside the GC oven which was cooled at -50 degrees C. The technique offered linearity over a ten fold concentration variation and sample volume range of 1-280 ml. The detection limit for 150 ml sample varied from 0.02-10 pptv depending on the compound.