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The earth's atmosphere is a complex mixture of many gases and their observations are incorporated in chemistry-climate models. Atmospheric observations have been the backbone of recent progress in atmospheric science, particularly about our understanding of the sun–atmosphere interaction causing chemical and radiative forcing linked to the environment and climate change. In terms of technology, there has been significant progress in both in situ and remote sensing measurements of several variables in the lower atmosphere. Among them, trace gases play an important role in climate change and several environmental problems. The recent progress in both in situ and remote sensing-based instrumentation has enabled researchers to study various atmospheric processes in great detail. For example, gas chromatography-based instrumentation provides detection from simple to complex species present in the atmosphere at very low concentrations. The laser-based spectroscopic instruments are emerging tools for fast response measurements of trace gases, which are important to understand rather short-term processes. The proton transfer reaction-mass spectrometry is regarded as one of the best technologies for the detection of numerous but specific types of trace gases, namely volatile organic compounds. However, there are advantages and disadvantages of any instrument in terms of quality of data, comprehensiveness and cost. In this article, we discuss the recent progress in instrumentation used for the measurement of trace gases in the lower atmosphere utilizing space, aircraft and satellitebased platforms as well as some laboratory techniques. We also briefly highlight the progress made during the past couple of decades, present status and future scenarios of trace gas measurements in the South Asia region. [ABSTRACT FROM AUTHOR]

Thousands of volatile organic compounds (VOCs) in the Earth's atmosphere exist which play an important role in various photochemical processes. However, the global model simulations of tropospheric chemistry deal with limited data of speciated VOCs. In the present study, we have used the Global Fire Emissions Database inventory of VOCs emitted from biomass burning in India during the period from 1997 to 2009. We have also analysed data of some VOCs measured in the upper troposphere over India for the year 2008. In this study, the major species analysed are C2H4, C2H4O, C2H6, C2H6S, C3H6, C3H6S, C3H8, C5H8, CH3OH, higher alkanes, higher alkenes, terpenes and toluene lumps. The biomass burning emissions of VOCs show large inter-annual variation. For example, the annual emission estimates of non-methane hydrocarbons (NMHCs) and CH3OH varied in the range 100-470 and 46-211 Gg yr-1 respectively. The major biomass sources were broadly categorized as deforestation, fuel-wood, forest and agricultural residues. The agricultural residue burning is the most dominant among the several biomass burning sources contributing to the emissions of CH3OH (59%), isoprene (80%) and toluene (72%). On the other hand, the major sources for NMHCs emission were agricultural residues and deforestation during all the years. The fire count data detected using the satellite-based Along Track Scanning Radiometer have been used to directly refer to the seasonal and inter-annual variations of biomass burning activities. We have estimated the propylene-equivalent concentrations of different light NMHCs measured in the upper troposphere over India. Role of stratospheric intrusion in the distribution of NMHCs has been analysed using the potential vorticity data. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) are ubiquitous atmospheric constituents of both anthropogenic and natural origin. VOCs are important precursors of tropospheric ozone (O3), and can impact air quality and global climate. Most of primary VOCs and their oxidized products makeup a major fraction of secondary pollutants in urbanized regions. Due to fast reaction rates mainly with the hydroxyl radical (OH), the VOCs control the oxidizing capacity of the troposphere. Measurements of VOCs are important to study the photochemical transformation, both qualitatively and quantitatively. Many aspects of VOCs in the atmosphere remain poorly understood - these include the detection and quantification of by-products of VOCs, their oxidation reactions and their role in oxidant and secondary aerosol formation. In the photochemistry of tropical troposphere, VOCs play a key role due to high abundance of water vapour (H2O) and intense solar radiation flux. Measurements of these species are rare over the Indian subcontinent and surrounding marine regions. Traditionally, gas chromatography-based methods have been used for the detection of VOCs. Recently, the fast time response and sensitive techniques like proton-transfer reaction mass spectrometer are the emerging tools to detect trace levels of various VOCs in the atmosphere. [ABSTRACT FROM AUTHOR]

The relationship between surface-level observations of daily maxima in ozone (O3max) volume mixing ratio and ambient air temperature (Tmax) has been studied at an urban site, i.e. Pune (18.4°N, 73.8°E), India during 2003-04. The mixing ratios of O3max were found to be highest during winter to pre-monsoon period and lowest in the monsoon season. The dependence of O3max levels on Tmax has been quantified using the linear regression fit for the different seasons. However, except for the monsoon season, reasonably good correlations between O3max and Tmax were noticed. The correlation between daily O3max concentration and minimum NOx (NOxmin) concentration was also studied to assess the importance of photochemical mechanism mainly reduction in the loss due to titration. Overall, the strong dependencies of O3max on Tmax and NOxmin signify the role of both meteorological and photochemical processes during most months of a year. The positive slopes of ▵ O3max/▵ Tmax and ▵ O3max/▵ NOxmin clearly indicate the role of significant production and accumulation of O3 under high temperature and low NOx conditions respectively, during winter and premonsoon seasons. The statistical analysis of O3 in relation with the key meteorological and chemical parameters is important to understand the sensitivity of secondary pollutants on various controlling factors. [ABSTRACT FROM AUTHOR]