Compositional Constraints are Vital for Atmospheric PM_2.5 Source Attribution over India.

Area of Science:

• Atmospheric Chemistry and Physics
• Environmental Science and Policy
• Public Health and Epidemiology

Background:

• India contends with some of the world's highest ambient fine particulate matter (PM2.5) pollution levels.
• A lack of in situ measurements has historically limited the evaluation of chemical transport models used for PM2.5 exposure estimation in the region.
• Accurate source attribution of PM2.5 is crucial for effective air quality management and health assessments in India.

Purpose of the Study:

• To evaluate and improve chemical transport models for PM2.5 simulation in India using novel airborne measurements.
• To constrain ammonia and nitrogen oxide emissions using satellite observations.
• To provide an accurate, model-based estimation of population-weighted PM2.5 exposure and associated health impacts.

Main Methods:

• Conducted a model comparison using speciated airborne measurements of fine aerosol.
• Incorporated process-level changes into the chemical transport model.
• Utilized satellite data from Cross-track Infrared Sounder (CrIS) and TROPOspheric Monitoring Instrument (TROPOMI) to constrain emissions.

Main Results:

• The improved model simulation showed significantly reduced bias compared to the baseline, particularly for ammonium and nitrate simulations.
• Validated simulation estimated a population-weighted annual PM2.5 exposure of 61.4 μg m⁻³.
• Identified residential, commercial, and other (RCO) sectors (21%) and the energy sector (19%) as major contributors to PM2.5, with an estimated 961,000 attributable deaths.

Conclusions:

• Speciated observational constraints are critical for developing accurate PM2.5 aerosol source attribution models.
• The improved model provides a more reliable basis for understanding PM2.5 exposure and its health consequences in India.
• Enhanced model accuracy supports targeted air quality management strategies and public health interventions.