Volatile organic compounds and their measurements in the troposphere

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.