My PhD research in Atmospheric Chemistry was focused on the measurement of volatile organic compounds in the ambient air and various emission sources active over the North-west Indo-Gangetic Plain. The research consisted of laboratory experiments and field measurements using Thermal desorption-Gas Chromatography-Flame ionisation detection (TD-GC-FID), Proton Transfer Reaction Mass Spectrometer (PTR-MS), cavity ring-down spectrometer (CRDS) greenhouse gas analyser, trace level analysers for ambient measurements of ozone, nitrogen oxides, carbon monoxide, sulfur dioxide, PM10 and PM2.5.
1. Non-methane hydrocarbon (NMHC) fingerprints of major urban and agricultural emission sources in South Asia
Source profiles from different emission sources provide valuable insights into the role of NMHC emissions in air pollution. I investigated the NMHC source profiles as chemical fingerprints of major urban and agricultural emission sources that are active in South Asia, such as paddy stubble burning, garbage burning, idling vehicular exhaust from petrol, diesel, LPG and CNG vehicles, and evaporative fuel emissions from petrol, diesel and LPG.
During this work I collected >100 whole air samples of emissions from different sources and analysed them using a TD-GC-FID that was optimised for the measurement of NMHCs following the recommendations of World Meteorological Organisation (WMO).
The results from this work were published in the peer-reviewed journal Atmospheric Chemistry and Physics (ACP):
Non-methane hydrocarbon (NMHC) fingerprints of major urban and agricultural emission sources for use in source apportionment studies.
During this work I collected >100 whole air samples of emissions from different sources and analysed them using a TD-GC-FID that was optimised for the measurement of NMHCs following the recommendations of World Meteorological Organisation (WMO).
The results from this work were published in the peer-reviewed journal Atmospheric Chemistry and Physics (ACP):
Non-methane hydrocarbon (NMHC) fingerprints of major urban and agricultural emission sources for use in source apportionment studies.
2. A hybrid emission inventory for the paddy stubble burning emissions in North-west India
Every year, the densely populated northwest Indo-Gangetic Plain (NW-IGP) experiences episodes of massive paddy stubble burning during the post-monsoon season (October and November), which aggravates the regional air pollution considerably. The transport of these emissions also results in widespread smog and poor air quality in densely populated villages and cities, even several hundred kilometres downwind of burnt areas.
There was a huge knowledge gap regarding the emission factors of speciated VOCs from this practice, along with considerable uncertainties in the local and global fire emission inventories that relied on the Satellite fire data and did not account for local crop varieties, burning practices and environmental conditions.
In this project, I developed a novel “hybrid” gridded emission inventory of 77 VOCs and all criteria air pollutants emitted from paddy stubble burning over Punjab and Haryana in 2017 at 1 km x 1 km spatial resolution. For this, I first calculated the emission factors of 77 VOCs, which were measured in the smoke samples collected from the on-field paddy fires of villages in Punjab. These were then combined with 1 km × 1 km stubble burning activity, which was constrained by district-level annual crop production yields and satellite-detected fires.
The results from this work were published in the the peer-reviewed journal Science of The Total Environment (STOTEN):
Gridded 1 km × 1 km emission inventory for paddy stubble burning emissions over north-west India constrained by measured emission factors of 77 VOCs and district-wise crop yield data.
There was a huge knowledge gap regarding the emission factors of speciated VOCs from this practice, along with considerable uncertainties in the local and global fire emission inventories that relied on the Satellite fire data and did not account for local crop varieties, burning practices and environmental conditions.
In this project, I developed a novel “hybrid” gridded emission inventory of 77 VOCs and all criteria air pollutants emitted from paddy stubble burning over Punjab and Haryana in 2017 at 1 km x 1 km spatial resolution. For this, I first calculated the emission factors of 77 VOCs, which were measured in the smoke samples collected from the on-field paddy fires of villages in Punjab. These were then combined with 1 km × 1 km stubble burning activity, which was constrained by district-level annual crop production yields and satellite-detected fires.
The results from this work were published in the the peer-reviewed journal Science of The Total Environment (STOTEN):
Gridded 1 km × 1 km emission inventory for paddy stubble burning emissions over north-west India constrained by measured emission factors of 77 VOCs and district-wise crop yield data.
3. Ambient measurements of NMHCs over Indo-Gangetic Plain
In this project, I carried out the ambient measurements and source analyses of rarley measured 52 ozone precursor NMHCs over the cities of Delhi and Mohali during wintertime (Dec 2016-Jan 2017).
The results not only provided valuable information on the winter time ambient concentrations and diurnal trend, but also suggested traffic and LPG usage as the major emission sources of NMHCs in North India. Within the traffic source, gasoline/petrol-fuelled vehicles with older emission control were identified as the major NMHC emitters.
Additionally, we also investigated the night time oxidation chemistry over the Indo-Gangetic Plain (IGP) by comprehensively measuring the precursors and sinks of Stabilized Criegee Intermediates (SCI) during the summer season. The results showed that the pollution events influenced by crop burning resulted in significantly elevated SCI production and this oxidation pathway could be a significant source of fine mode sulfate aerosols over the Indo-Gangetic Plain during summer season influenced by crop residue burning.
The results from this work were published in the the peer-reviewed journal Science of The Total Environment (STOTEN):
Probing wintertime air pollution sources in the Indo-Gangetic Plain through 52 hydrocarbons measured rarely at Delhi & Mohali.
Sources, sinks, and chemistry of Stabilized Criegee Intermediates in the Indo-Gangetic Plain.
The results not only provided valuable information on the winter time ambient concentrations and diurnal trend, but also suggested traffic and LPG usage as the major emission sources of NMHCs in North India. Within the traffic source, gasoline/petrol-fuelled vehicles with older emission control were identified as the major NMHC emitters.
Additionally, we also investigated the night time oxidation chemistry over the Indo-Gangetic Plain (IGP) by comprehensively measuring the precursors and sinks of Stabilized Criegee Intermediates (SCI) during the summer season. The results showed that the pollution events influenced by crop burning resulted in significantly elevated SCI production and this oxidation pathway could be a significant source of fine mode sulfate aerosols over the Indo-Gangetic Plain during summer season influenced by crop residue burning.
The results from this work were published in the the peer-reviewed journal Science of The Total Environment (STOTEN):
Probing wintertime air pollution sources in the Indo-Gangetic Plain through 52 hydrocarbons measured rarely at Delhi & Mohali.
Sources, sinks, and chemistry of Stabilized Criegee Intermediates in the Indo-Gangetic Plain.
4. Road Transport Emission Inventory of India (RTEII) and air pollution scenario analyses of fleet replacement strategies
In this project, I was part of the research team in IISER Mohali that developed the first detailed chemically speciated (74 VOCs) and high spatially resolved (0.1° × 0.1°) national emission inventory for road-traffic sector emissions over India. We measured the emission factors and updated the fuel usage and vehicular fleet activity data over India, thus providing a significant advancement over previous emission quantifications from the road sector over India. We also examined the “what-if” intervention scenarios with the introduction of electric vehicles and greener fuels in India.
The results identified LPG 3-wheelers and petrol 2-wheelers as the most polluting vehicles and a strategy of replacement of these vehicles to the electrical alternatives and diesel heavy duty vehicles to CNG alternatives significantly improved the air quality over India.
The results from this work were published in the the peer-reviewed journal Atmospheric Environment: X:
RTEII: A new high-resolution (0.1° × 0.1°) road transport emission inventory for India of 74 speciated NMVOCs, CO, NOx, NH3, CH4, CO2, PM2.5 reveals massive overestimation of NOx and CO and missing nitromethane emissions by existing inventories.
Air pollution scenario analyses of fleet replacement strategies to accomplish reductions in criteria air pollutants and 74 VOCs over India.
The results identified LPG 3-wheelers and petrol 2-wheelers as the most polluting vehicles and a strategy of replacement of these vehicles to the electrical alternatives and diesel heavy duty vehicles to CNG alternatives significantly improved the air quality over India.
The results from this work were published in the the peer-reviewed journal Atmospheric Environment: X:
RTEII: A new high-resolution (0.1° × 0.1°) road transport emission inventory for India of 74 speciated NMVOCs, CO, NOx, NH3, CH4, CO2, PM2.5 reveals massive overestimation of NOx and CO and missing nitromethane emissions by existing inventories.
Air pollution scenario analyses of fleet replacement strategies to accomplish reductions in criteria air pollutants and 74 VOCs over India.
5. Open Municipal Waste Burning In India (OWEBII)
In this project, I was part of the research team in IISER Mohali comprising of the Atmospheric Chemistry & Emissions Research Group and Aerosol Research Group, that developed a new municipal open waste burning emission inventory from India (OWBEII), at a resolution of 0.1° × 0.1°. We measured the emission factors of 59 non-methane volatile organic compounds (NMVOCs), CH4, CO2, CO, and NOx from the garbage fires in rural and urban sites in India.
The results not only identified MSW burning as an important emerging emission source in India, but also highlighted the importance to account for social inequalities in developing regions for accurate estimation of waste generation and burning.
The results from this work were published in the the peer-reviewed journal Environmental Science & Technology (ES&T):
Gridded Emissions of CO, NOx, SO2, CO2, NH3, HCl, CH4, PM2.5, PM10, BC, and NMVOC from Open Municipal Waste Burning in India.
The results not only identified MSW burning as an important emerging emission source in India, but also highlighted the importance to account for social inequalities in developing regions for accurate estimation of waste generation and burning.
The results from this work were published in the the peer-reviewed journal Environmental Science & Technology (ES&T):
Gridded Emissions of CO, NOx, SO2, CO2, NH3, HCl, CH4, PM2.5, PM10, BC, and NMVOC from Open Municipal Waste Burning in India.
6. Biogenic emissions from the vegetation and their impact on atmospheric chemistry
In this project (2017-2020), I was part of the research team in IISER Mohali comprising of the Atmospheric Chemistry & Emissions Research Group and Aerosol Research Group, that carried out the measurement of biogenic VOC emissions from different tree species using the branch enclosure methodology and modelled the impact of these emissions on the regional air quality and climate.
The results identified Mahogany (Swietenia macrophylla King) as a significant emitter and one of the missing natural sources of ambient DMS and allowed us to develop a new index to assess the air quality impact of various tree species, which will help the policy makers to plan urban plantations. Our results also showed that the agreement between model and measurements can be improved by accounting for the missing cropland trees and an expansion of this agroforestry practice can have significant impacts over future climate mitigation and food security efforts over NW-IGP.
The results from this work were published in the the peer-reviewed journals Science of The Total Environment (STOTEN), Atmospheric Chemistry and Physics (ACP) and Urban Climate :
Significant emissions of dimethyl sulfide and monoterpenes by big-leaf mahogany trees: discovery of a missing dimethyl sulfide source to the atmospheric environment.
Cropland trees need to be included for accurate model simulations of land-atmosphere heat fluxes, temperature, boundary layer height, and ozone.
A new index to assess the air quality impact of urban tree plantation.
The results identified Mahogany (Swietenia macrophylla King) as a significant emitter and one of the missing natural sources of ambient DMS and allowed us to develop a new index to assess the air quality impact of various tree species, which will help the policy makers to plan urban plantations. Our results also showed that the agreement between model and measurements can be improved by accounting for the missing cropland trees and an expansion of this agroforestry practice can have significant impacts over future climate mitigation and food security efforts over NW-IGP.
The results from this work were published in the the peer-reviewed journals Science of The Total Environment (STOTEN), Atmospheric Chemistry and Physics (ACP) and Urban Climate :
Significant emissions of dimethyl sulfide and monoterpenes by big-leaf mahogany trees: discovery of a missing dimethyl sulfide source to the atmospheric environment.
Cropland trees need to be included for accurate model simulations of land-atmosphere heat fluxes, temperature, boundary layer height, and ozone.
A new index to assess the air quality impact of urban tree plantation.
7. Winter Fog Experiment (WIFEX) and Odd-even traffic rule in Delhi
The Winter Fog Experiment (WIFEX) was an observational campaign (2015-2019) conducted at the Indira Gandhi International Airport, New Delhi by the Indian Institute of Tropical Meteorology (IITM), India Meteorology Department (IMD), National Center for Medium Range Weather Forecast (NCMRWF), Airport Authority of India, GMR, Indira Gandhi International Airport and Indian Institute of Science Education and Research (IISER) Mohali. The main objective of the campaign was to study the physical and chemical characteristics of fog and the various physio-chemical processes responsible for its genesis, sustenance and dissipation. I was part of the research team from IISER Mohali that studied the role of VOCs in the fog dynamics and chemistry during the campaign.
The results showed that there existed a emission feedback system during the cold foggy periods, when open biomass burning was enhanced for the heating purposes in Delhi. This enhanced activity resulted in the emission of gaseous and particulate pollutants, which inturn influenced the fog chemistry, its sustenance and intensity.
During the severe wintertime air pollution in 2016, the State Government of Delhi implemented the "odd-even traffic rule" from 1-15 January, 2016. The rule mandated that only odd license-plate private four-wheelers/cars could ply between 08:00 and 20:00 local time on odd days and only even license-plate numbered private four wheelers/cars could play on even days. The aim was to address the severe wintertime pollution episodes in the Delhi NCR region by targeting the most contributing source: Traffic emissions. Our research team studied the impact of this trial policy by collecting the whole air samples from busy traffic junctions and analysing them for VOCs, CO, CH4 and CO2. The results showed that this policy did not result in anticipated reductions in traffic emissions, likely due to the changed temporal and fleet emission behaviour.
The results from these projects were published in the the peer-reviewed journals Science of The Total Environment (STOTEN) and Current Science:
Winter fog experiment over the Indo-Gangetic plains of India.
Odd–Even Traffic Rule Implementation during Winter 2016 in Delhi Did Not Reduce Traffic Emissions of VOCs, Carbon Dioxide, Methane and Carbon Monoxide.
Volatile organic compound measurements point to fog-induced biomass burning feedback to air quality in the megacity of Delhi.
The results showed that there existed a emission feedback system during the cold foggy periods, when open biomass burning was enhanced for the heating purposes in Delhi. This enhanced activity resulted in the emission of gaseous and particulate pollutants, which inturn influenced the fog chemistry, its sustenance and intensity.
During the severe wintertime air pollution in 2016, the State Government of Delhi implemented the "odd-even traffic rule" from 1-15 January, 2016. The rule mandated that only odd license-plate private four-wheelers/cars could ply between 08:00 and 20:00 local time on odd days and only even license-plate numbered private four wheelers/cars could play on even days. The aim was to address the severe wintertime pollution episodes in the Delhi NCR region by targeting the most contributing source: Traffic emissions. Our research team studied the impact of this trial policy by collecting the whole air samples from busy traffic junctions and analysing them for VOCs, CO, CH4 and CO2. The results showed that this policy did not result in anticipated reductions in traffic emissions, likely due to the changed temporal and fleet emission behaviour.
The results from these projects were published in the the peer-reviewed journals Science of The Total Environment (STOTEN) and Current Science:
Winter fog experiment over the Indo-Gangetic plains of India.
Odd–Even Traffic Rule Implementation during Winter 2016 in Delhi Did Not Reduce Traffic Emissions of VOCs, Carbon Dioxide, Methane and Carbon Monoxide.
Volatile organic compound measurements point to fog-induced biomass burning feedback to air quality in the megacity of Delhi.