Estimates of submicron particulate matter (PM1) concentrations for 1998-2022 across the contiguous USA: leveraging measurements of PM1 with nationwide PM2·5 component data
1Department of Energy, Environmental and Chemical Engineering, Washington University in St Louis, St Louis, MO, USA.
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Summary
Submicron particulate matter (PM1) concentrations in the USA decreased significantly from 1998-2022, driving much of the fine particulate matter (PM2.5) reduction. This highlights the need to assess PM1 health impacts separately from PM2.5.
Area of Science:
- Environmental Health Sciences
- Atmospheric Chemistry
- Epidemiology
Background:
- Estimates of health risks from fine particulate matter (PM2.5) vary due to differences in aerosol size and composition.
- Submicron particulate matter (PM1) may have stronger health impacts than PM2.5, but long-term US data has been lacking.
- This study addresses the data gap by estimating PM1 concentrations across the USA from 1998-2022.
Purpose of the Study:
- To estimate biweekly ambient PM1 concentrations and their uncertainties across the contiguous USA from 1998-2022.
- To analyze the spatial and temporal trends of PM1 concentrations.
- To investigate the relationship between PM1 and PM2.5 concentrations and their components.
Main Methods:
- Developed hybrid estimates of PM2.5 chemical composition using satellite retrievals, air quality modeling, and ground monitoring.
- Estimated biweekly gapless ambient PM1 concentrations at 1 km² resolution.
- Constrained PM1 mass fractions using observational data for major components and scientific understanding for others.
Main Results:
- PM1 concentrations showed significant spatial variation, with higher levels in the east, urban/industrial areas, and wildfire-affected regions.
- Population-weighted mean (PWM) PM1 decreased significantly (-0.23 μg/m³ per year) from 1998-2022, accounting for 86% of the PM2.5 reduction.
- The PM1/PM2.5 ratio also decreased, indicating a shift towards coarser PM2.5, likely due to reduced emissions from combustion sources.
Conclusions:
- The significant reduction in PM1, a major component of PM2.5, reflects successful air quality regulations targeting fossil fuel and combustion sources.
- The decreasing PM1/PM2.5 ratio suggests a gradual coarsening of PM2.5, necessitating separate health impact assessments for PM1 and PM2.5.
- Future monitoring, health studies, and regulatory efforts should incorporate PM1 alongside PM2.5 for comprehensive environmental health protection.