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ACE

Aerosol Characterization and receptor modEling Group

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Hybrid Model Resolved Impacts of COVID‐19 Lockdowns on PM2.5 Sources in Bhopal, India: Role of Meteorology, Secondary Inorganic Aerosols, and Crop Residue Burning

Pullokaran, D., Sunder Raman, R.*, Bhardwaj, A., Haswani, D., Shukla, D.
Journal of Geophysical Research: Atmospheres, 25 January 2026, 131.

Air pollution in India is complex due to the multitude of sources and varying topography, rendering the interplay between meteorology and emission sources significant. To address this challenge, this work presents an integrated methodology for PM2.5 source apportionment in Bhopal, central India, combining dispersion-normalized positive matrix factorization (DN-PMF) with a machine-learning interpretability approach using Random Forest and SHAP (RF-SHAP). DN-PMF improves conventional source identification by incorporating air dilution effects, yielding refined source contributions for nine factors in Bhopal. Seasonal factor contributions peaked during periods with a lower boundary layer height, such as secondary sulfate during the winter season (21.3 μg m−3, 31.7%). The COVID-19 lockdowns, a quasi-natural emissions reduction experiment, led to a decrease in aerosol contributions from industrial, residential and traffic-related sources. However, during this period, crop residue burning was exposed as a major anthropogenic contributor, which together with unfavorable meteorology resulted in increased mean PM2.5 (50.6 ± 24.3 μg m−3) during the lockdowns compared to the reference period (36.7 ± 9.7 μg m−3). Using RF-SHAP the influence of meteorology and emission sources in driving secondary inorganic aerosol formation was examined. Secondary nitrate and residential fuel were identified as key contributors to exceedances of the Indian National Ambient Air Quality Standards (60 μg m−3, 24-hr average) at the study site. Integrating DN-PMF with RF-SHAP (driver analysis) enhanced source attribution by linking source contributions with their driving factors, establishing a framework for assessing pollution dynamics. This framework can help strengthen improved air quality initiatives in India, including the national Smart Cities Mission.


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Understanding PM-bound trace element solubilities: Controls, anthropogenic and natural sources

Haswani, D., Sunder Raman, R.*
Environmental Pollution, 11 July, 2025, 126823.

Heavy metal pollution in fine particulate matter (PM2.5) is a subject of great concern due to rapid urbanization and industrialization. To evaluate the chemical characteristics and sources of PM in PM2.5, 2.5-bound trace elements (TEs) chemical fractions of two-year (2019–2020) key TEs (Al, Si, Ca, Fe, Ti, K, S, P, Mn, Ni, V, Cr, Cu, Zn and Pb) were investigated. A four-step sequential extraction method was adopted to extract and analyse TEs exchangeable, reducible, oxidisable and residual fractions using inductively coupled plasma optical emission spectrometry. Positive Matrix Factorization was applied to the fractional concentrations of individual elements to apportion TE sources in PM2.5. The model resolved factors were identified as i) mineral dust ii) agricultural crop burning residues iii) vehicular emission iv) coal combustion residues, and v) industrial emission. Mobility of elements from geogenic sources increased during 2020 (COVID 19 lockdowns year), likely due to the formation of soluble secondary inorganic species, while mobility of elements from anthropogenic sources decreased. These findings suggest that anthropogenic activities influence not only TE abundance but also their solubility and bioavailability.




* Corresponding author
# Title Year
* Presenting author

  • Sayak Patra*, Ramya Sunder Raman. "Aeroquant Software: An Energy and Cost-Effective Rapid Solution for Aerosol Chemical Characterization from Teflon Filters Using Machine Intelligence". The 14th Asian Aerosol Conference (AAC-2025) organized by the Indian Aerosol Science and Technology Association (IASTA) at Mumbai, India (1-4 Dec, 2025).

  • Delwin Pullokaran*, Ankur Bhardwaj, Diksha Haswani, Ramya Sunder Raman, Deeksha Shukla, Abisheg Dhandapani, Jawed Iqbal, R. Naresh Kumar, Sadashiva Murthy B. M. and S. V. Laxmi Prasad - Advancing PM2.5 Source Apportionment through Dispersion Normalized PMF: A Comprehensive Study across India at the European Geosciences Union Conference, April 27 - May 2 2025, Vienna, Austria. "https://doi.org/10.5194/egusphere-egu25-1087" .

  • Delwin Pullokaran*, Ankur Bhardwaj, Diksha Haswani, Deeksha Shukla, Ramya Sunder Raman, Abisheg Dhandapani, Jawed Iqbal, R. Naresh Kumar, Sadashiva Murthy B. M. and S. V. Laxmi Prasad - Regional and Transboundary Aerosols at Three COALESCE Sites in India: Understanding the Sources and Processes at the American Geosciences Union Conference, December 9, 2024, Washington, DC.

  • Diksha Haswani* and Ramya Sunder Raman. "Chemical fractionation and potential health risks assessment of particulate matter bound heavy metals in Bhopal, Central India." EGU General Assembly Conference Abstracts. 2024. 10.5194/egusphere-egu24-239.

  • Diksha Haswani*, Ramya Sunder Raman, Kajal Yadav, Abisheg Dhandapani, Jawed Iqbal, R. Naresh Kumar, L. P. Sanyasihally Vasanth Kumar, Adi Yogesh, Sadashiva Murthy B. M. and K. S. Lokesh: Study of aerosol trace elements over three COALESCE network locations in India: Spatio-temporal variability, dry deposition and health risks, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6113. "https://doi.org/10.5194/egusphere-egu23-6113" .

  • Delwin Pullokaran*, Ramya Sunder Raman, Ankur Bhardwaj, Deeksha Shukla and Diksha Haswani. “Insights into the impact of COVID-19 lockdowns on USEPA PMF-5 derived PM2.5 source contributions at Bhopal, India”. European Geosciences Union Conference, April 26, 2023, Vienna, Austria

  • Kajal Yadav* and Ramya Sunder Raman. “Phthalate esters in atmospheric PM2.5 in Bhopal, central India: Identification, Concentrations, and Health Risk Assessment”.European Geosciences Union Conference, April 26, 2023, Vienna, Austria

  • Ankur Bhardwaj*, Kajal Yadav, Diksha Haswani and Ramya Sunder Raman. “Assessing the Impacts of COVID-19 lockdowns on Site-specific Optical properties of PM2.5 Carbonaceous components and Mineral dust at Bhopal, India”. The American Geophysical Union Conference, December 15, 2022, Chicago, USA

  • Kajal Yadav* and Ramya Sunder Raman. “Optimization of a Thermal Desorption - Gas Chromatography/ Mass Spectrometry method for the determination of Polycyclic Aromatic Hydrocarbons in ambient PM2.5 over Bhopal, central India ”. 22nd American Geophysical Union Fall meetting 2022, December 15, 2022, Chicago, USA

  • Delwin Pullokaran*, Ramya Sunder Raman, Ankur Bhardwaj, Deeksha Shukla, Diksha Haswani, Jawed Iqbal, Abisheg Dhandapani, R. Naresh Kumar, Sadashiva Murthy B. M., S. V. Laxmi Prasad and Prabhavathi Venkatesh. “Spatio-temporal trends of the relationship between surface PM2.5 and its chemical constituents across three locations in India: A mass closure investigation”. 11th International Aerosol Conference (IAC), September 8, 2022, Athens, Greece

  • Diksha Haswani*, Ramya Sunder Raman, Kajal Yadav. “Assessing the Pollution Characteristics of PM2.5 -bound Heavy Metals at Bhopal, Central India”. 11th International Aerosol Conference (IAC), September 8, 2022, Athens, Greece

  • Ankur Bhardwaj*, Kajal Yadav, Diksha Haswani, Ramya Sunder Raman. “Site-specific Mass Absorption Cross-section of Elemental Carbon, Brown Carbon, and Mineral Dust at Bhopal, Central India”. 11th International Aerosol Conference (IAC),September 8, 2022, Athens, Greece

  • Sandeep Devaliya*, Ramya Sunder Raman, Krishna Kedia, Amit Kesarkar, Jyoti Bhate, Vikas Singh, Kaushik Muduchuru, Arushi Sharma, Chandra Venkataraman.“Sensitivity to chemical mechanisms on the WRF-Chem generated aerosol fields over India”. 11th International Aerosol Conference (IAC), September 8, 2022, Athens, Greece

  • Prem Maheshwarkar*, Ramya Sunder Raman,Nirdesh Maravi. “Can we reliably use satellite derived AOD to estimate annual changes in PM2.5 concentrations during 2020 (Year with COVID induced lockdown)?”. 11th International Aerosol Conference(IAC), September 8, 2022, Athens, Greece

  • Kajal Yadav*, Ramya Sunder Ramya, Jayant Nirmalakar, Dhananjay Deshmukh, Md.Mozammel Haque. “Seasonal study of stable carbon and nitrogen isotopic composition in fine aerosols over Bhopal, central India”. 11th International Aerosol Conference (IAC), September 6, 2022, Athens, Greece

  • Rahul Wadhwani*, Deeksha Shukla, Ramya Sunder Raman, Abhisheg Dhandapani, R Naresh Kumar, Jawed Iqbal, S V L Prasad, Sadashiva Murthy B. M., K P Jithin. “Evaluation of Isorropia for aerosol acidity at three regional sites in COALESCE network”. 11th International Aerosol Conference (IAC), September 6, 2022, Athens, Greece

  • Sandeep Devaliya*, Prem Maheshwarkar, Ankur Bhardwaj, Diksha Haswani, Deeksha shukla, Amit Kesarkar. 2022." Evaluation of MERRA-2 PM2.5 mass and its constituent chemical species concentrations over a COALESCE network site in Bhopal,India. European Geosciences Union Conference, May 26, 2022, Vienna, Austria

  • Kajal Yadav*, Ramya Sunder Raman, Ankur Bhardwaj, Debajyoti Paul, Tarun Gupta, Kaggere Shivananjaiah Lokesh, and Laxmi Prasad Sanyasihally Vasanth Kumar: "Source quantification of PM2.5 using δ13C values along with corresponding organic carbon, elemental carbon, and select inorganic ions over two COALESCE network locations". European Geosciences Union Conference, May 24, 2022, Vienna, Austria

  • Ankur Bhardwaj*, Ramya Sunder Raman."Estimation of organic positive artefacts on Quartz filters and volatilization loss from Teflon filters at a COALESCE network site - Bhopal, India". European Geosciences Union Conference, May 23, 2022, Vienna, Austria

  • Sandeep Devaliya*, Jyoti Bhate, Ramya Sunder Raman, Kaushik Muduchuru, Arushi Sharma, Amit Kesarkar, Chandra Venkataraman. 2021."Chemistry Driven Changes in Simulated Meteorology for May 2015: WRF/WRF-Chem Studies over India". The American Geophysical Union Conference, December 12, 2021, New Orleans, USA

  • Sayantee Roy*, Rishabh Dev, Gazala Habib, Ramya Sunder Raman. 2021. "Wintertime Chemistry of Ionic and Carbonaceous Species of Fine Aerosol Particles at an Arid Desert Region in North-Western India". The American Association for Aerosol Research, October 18-22, 2021

  • Chimurkar Navinya*, Harish C Phuleria, Gupta Anurag, Pradnya Lokhande, Gazala Habib, Chandra Venkataraman, Abhijit Chatterjee, D. Abisheg, Anubha Goel, Arshid Jehangir, Yang Lian, Tuhin Kumar Mandal, Shiva Nagendra, Asif Qureshi, Ramya Sunder Raman, Binoy K. Saikia, Baerbel Sinha.2021."Fine Particulate Matter and Black Carbon Emissions from Non-Cooking Residential Sector Activities over Rural India". The American Association for Aerosol Research, October 18-22, 2021

  • Krishna Kedia*, Ramya Sunder Raman. 2020. “Light scattering by fine particles over a national park in central India: Comparisons between measurements and model outputs”. European Aerosol Conference, August 30, 2020

  • Gazala Habib*, Lovleen Gupta, Ramya Sunder Raman. 2019. “First long term measurements of PM2.5 and PM10 aerosol composition over Ghaziabad, India's most polluted industrial city”. Presented at the European Aerosol Conference, August 2019, Gothenburg, Sweden

  • Akanksha Singh*, Akarsh Ralhan, Ramya Sunder Raman, Gazala Habib, Ramakrishna Ramisetty, Nishant Mittal, Juergen Spielvogel, Axel Zerrath, Andrea Tiwari, Francisco Romay. 2019. “On-line size segregated mass measurement of aerosols from traditional cookstove emissions in central India using a Quartz Crystal Microbalance- Micro Orifice Uniform Deposition Impactor (QCM-MOUDI)”, Presented at the 11th Asian Aerosol Conference, May 2019, Hong Kong.

  • Jayant Nirmalkar*, Samresh Kumar, and Ramya Sunder Raman, "2018. Ambient Fine Pp Trace Elements over Van Vihar National Park, Bhopal, India and an Assessment of Associated Potential Health Risks". The American Association for Aerosol Research, St Louis Missouri, United State, September 2-7, 2018

  • Shilpi Samiksha* and Ramya Sunder Raman. 2018. “Usefulness of Stable Carbon Isotope and other Chemical Tracers to Distinguish between Primary and Secondary Sources of PM2.5 Pps over a National Park in Central India,International Aerosol Conference held during 2nd to 7th September 2018 in St. Louis , MO, USA

  • Samresh Kumar* and Ramya Sunder Raman, 2018. "Temporal Variability of Fine Pp Liquid Water Content over a National Park in Central India". Presented to 10th International Aerosol Conference, September 2018, St. Louis, MO, USA

  • Lovleen Gupta, and Ramya Sunder Raman, and Gazala Habib. 2018. "Chemical composition of ambient PM2.5 and PM10 for an industrial city, Ghaziabad, India". Presented at the 10th International Aerosol Conference, September 2018, St Louis, MO

  • Shilpi Samiksha*, Ramya Sunder Raman and Samresh Kumar. 2017. "Choice of OC/EC Ratio in the EC Tracer Method to Estimate Secondary Organic Carbon Over a National Park in Bhopal, India: A Sensitivity Analysis". Presented to Annual Meeting of the American Association for Aerosol Research, October 2017, Raleigh, NC

  • Samresh Kumar, Ramya Sunder Raman and Jayant Nirmalkar. 2017. "A Comparison of the Source Apportionment of Fine Pps Measured over a National Park in Central India using PMF2 and US EPA PMF5". Presented to Annual Meeting of the American Association for Aerosol Research, October 2017, Raleigh, NC

  • Jayant Nirmalkar*, Ramya Sunder Raman and Samresh Kumar. 2017. "Source Apportionment of PM2.5 Mass Over an Ecologically Sensitive Zone in Central India by Positive Matrix Factorization". Presented to Annual European Aerosol Conference, August 2017, Zurich, Switzerland

  • Shilpi Samiksha and Ramya Sunder Raman. 2017. "Anomalous Si/Al Ratios in PM10 and PM2.5 Road Dust at Several Locations in India". Presented to Annual European Aerosol Conference, August 2017, Zurich, Switzerland

  • Samresh Kumar and Ramya Sunder Raman. 2017. "Investigating the nature and sources of non-water soluble sulfate sulfur in fine pps over a National Park in Central India". Presented to Annual European Aerosol Conference, August 2017, Zurich, Switzerland

  • Ramya Sunder Raman*, Balram Ambade, Masood Ayub Kaloo. 2012. “Fine pps over an ecologically sensitive zone in Bhopal, India-characterization and temporal variability”. Presented to the 31st Annual Meeting of the American Association for Aerosol Research, October 2012, Minneapolis, MN

  • Ramya Sunder Raman*, Rohit Sirvaiya, Masood Ayub Kaloo. 2012. “Chemical source profiles for airborne crustal material over a region in India”. Presented to the 31st Annual Meeting of the American Association for Aerosol Research, October 2012, Minneapolis, MN

  • Ramya Sunder Raman*, S. Ramachandran, Sumita Kedia. 2010. “A methodology to estimate source-specific aerosol radiative forcing”. Presented to 29th Annual Meeting of the American Association for Aerosol Research, October 2010, Portland, OR

  • Ramya Sunder Raman, Philip K. Hopke*. 2007. “Descriptive time series analysis of fine carbonaceous aerosol at Potsdam, NY.” Presented to the European Aerosol Conference, September 2007, Salzburg, Austria

  • Ramya Sunder Raman*, Philip K. Hopke. 2006. “Investigation of carbonaceous aerosol behavior at two locations in New York State.” Presented to the International Aerosol Conference, September 2006, St. Paul, MN

  • Ramya Sunder Raman*, Philip K. Hopke, Eugene Kim, Potsdam, NY; Nicolas Bukowiecki, Ferenc Hegedus, Ernest Weingartner, Urs Baltensperger, Matthias Hill, Robert Gehrig, Peter Linemann, Gerald Falkenberg. 2005. “Source apportionment of the ambient aerosol in Zürich, Switzerland” Presented to the American Association for Aerosol Research, October 2005, Austin, TX

  • Ramya Sunder Raman*, Philip K. Hopke. 2005. “Source apportionment of fine pps in Potsdam and Stockton, NY, utilizing the composition of water-soluble short-chain organic acids.” Presented to the Particulate Matter Supersites Program and Related Studies. An international specialty conference sponsored by American Association for Aerosol Research. February 2005, Atlanta, GA

  • Ramya Sunder Raman*, Philip K. Hopke. 2005. “An ion chromatographic method for analysis of water-soluble short-chain organic acids in ambient particulate matter” Presented to the Particulate Matter Supersites Program and Related Studies. An international specialty conference sponsored by American Association for Aerosol Research. February 2005, Atlanta, GA

  • Ramya Sunder Raman*, Philip K. Hopke. 2004. “Analysis of water soluble short chain organic acids in ambient particulate matter.” Presented to the American Association for Aerosol Research , October 2004, Atlanta, GA