Emissions diurnal variability and modelling of biogenic volatile organic compounds

Abstract

Biogenic volatile organic compounds are emitted from vegetation and play key roles in atmospheric chemistry, air quality and climate. Isoprene which is mainly emitted from trees and shrubs is the major contributor to the global biogenic budget, with annual emissions of about 600 Tg/year. Trees can emit biogenic compounds and impact the micrometeorology by modulating the surface sensible and latent heat flux through transpiration and evaporative cooling while also uptaking carbon dioxide during photosynthesis. Biogenic emissions are poorly constrained over the northwest Indo-Gangetic Plain which is one of the most under-studied regions of the world in terms of atmospheric emissions and chemistry. Farmers in northwest Indo-Gangetic Plain like many other regions of the world, practice mixed agroforestry due to which the croplands have large swathes of poplar and eucalyptus. These trees are strong isoprene emitters.The monsoon season which is characterized by strong convective activity provide ideal conditions for assessing biogenic emissions as it is a period characterized by the maximum signal to noise ratio for the biogenic emissions and sources. During this season, vegetation throughout the region is not limited by availability of moisture while many anthropogenic fire sources which can also emit VOCs are absent. This thesis investigates the complex interplay of biogenic emissions,micrometeorology, atmospheric chemistry and land use land cover using ground-based measurements of isoprene and its oxidation products by a high sensitivity proton transfer reaction mass spectrometer (PTR-MS), high-resolution land use land cover satellite data along with the Weather Research and Forecasting model coupled with online chemistry (WRF-Chem) and the Model of Emissions of Gases and Aerosol from Nature (MEGAN). In the first part of my thesis work, I reported and analyzed the measurements for isoprene, formaldehyde, methyl vinyl ketone, methacrolein and acetaldehyde performed in July, August and September months at a sub-urban