Sources of non-methane volatile organic compounds in Delhi, India

Cities in India consistently feature amongst the most polluted in the world, with air quality problems driven by rapid and poorly regulated economic growth and development. Many sources emit non-methane volatile organic compounds (NMVOCs), which degrade local and regional air quality through the photochemical formation of tropospheric ozone and secondary organic aerosol (SOA). Large uncertainties in the understanding of NMVOC sources specific to India result in poorly constrained regional policy and global chemical transport models. Consequently, the drivers of the consistently observed poor air quality remain poorly understood.
This thesis presents measurements of NMVOCs made in Delhi during pre- and post-monsoon seasons in 2018. The sources of NMVOCs were examined, which showed that NMVOC emissions were principally from petrol and diesel related sources. Very high NMVOC concentrations were measured at night during the post-monsoon campaign. These were shown to be emissions from the local area and were enhanced due to stagnant conditions caused by very low planetary boundary layer heights and windspeeds.

Solid fuels represent a large energy source to India, with potentially significant impacts to air quality. Consequently, a detailed source study of organic emissions from solid-fuel combustion sources was conducted. Firstly, a new method for collecting intermediate-volatility and semi-volatile organic gases and particles onto solid-phase extraction disks and Teflon filters, followed by solvent extraction with analysis by two-dimensional gas chromatography coupled to time-of-flight mass spectrometry was evaluated. Secondly, an extremely detailed set of emission factors of NMVOCs were measured with a range of online gas-phase techniques. These results were then mapped onto a volatility-basis dataset and the SOA production potential and OH reactivity of different sources compared. Finally, a high-resolution bottom-up emission inventory was developed for India from 1993-2016. This found that burning of cow dung cake had a disproportionately large impact to NMVOCs from residential combustion.