Variabilities in Trace Gases and Meteorological Parameters over the Himalayan and Associated Regions
Prajjwal S. Rawat
Date & Time :
The impacts of escalating emissions of air pollutants are now one of South Asia's most pressing environmental concerns, particularly in Northern India. Additionally, the adjacent Himalayas lead to the confinement of these pollutants and transport them to greater horizontal and vertical extents.. Along the way, the primary emissions also get transformed into secondary pollutants such as ozone. However, our understanding of episodic events and ozone variations are limited over such regions owing to the sparsity of in-situ observations and lack of comprehensive validation of space-based retrievals. To address this issue, we performed observations from ozonesonde and MAX-DOAS and analyzed satellite data. Firstly, the ozone profile and total ozone retrieval from Indian satellite INSAT-3D at a high spatio- temporal resolutions are assessed over the central Himalaya. Eventually the poor retrieval performance is improved in INSAT-3DR using an improved radiance intercalibration and apriori information in inversemodellingandmachinelearningtechniques.Furthermore,AIRS/NASA,IASI/ESA, CrIS/NOAA satellite ozone retrieval are compared against balloon-borne (ozonesonde) observations convolved with satellite averaging kernel and a-priori. The larger differences are observed in the upper troposphere and lower stratospheric regions. However, both balloon borne and AIRS satellite observation over the subtropical Himalayas detected frequent tropopause folding during the winter and spring leading to a 5 - 25% increase in ozone over the middle and upper troposphere. Whereas ozone increased by 10 - 20% during biomass burning periods in the lower troposphere. The estimated ozone UV radiative forcing over the Himalayas is increasing and matches well between ozonesonde (4.86 mW/m2) and OMI (4.04 mW/m2), while significant underestimation is seen in AIRS satellite RF calculations (2.96 mW/m2) due to large uncertainties in the total ozone observations. The MAX-DOAS and satellite observations (TROPOMI and GOME-2) captured systematic monthly variations in NO2, SO2, HCHO, and CHOCHO vertical column densities (VCDs) depending on their sources and photochemistry.Moreover,MAX-DOAScomparisonwiththesatelliteobservationshows underestimation up to 30% for satellite NO2VCDs, while SO2, HCHO, and CHOCHO VCDs agree well. Rgfsensitivity calculation shows prominent biogenic sources of VOCs during noon hours. Rfn calculation mostly shows NOxlimited ozone production regime over the Himalayan foothill. The satellite remote sensing observations are also utilized to study the influence of the Indian lockdown on the changes in vertical profile and columnar amounts of trace gases over the Indian region and various contrary effects are observed.
About Speaker :
Prajjwal S. Rawat is a Ph.D. student at ARIES and this is his pre-thesis submission talk.