Assessing uncertainties of a geophysical approach to estimate surface fine particulate matter distributions from satellite-observed aerosol optical depth
<p>Health impact analyses are increasingly tapping the broad spatial coverage of satellite aerosol optical depth (AOD) products to estimate human exposure to fine particulate matter (PM<span class="inline-formula"><sub>2.5</sub></span>). We use a forward geoph...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/295/2019/acp-19-295-2019.pdf |
| Summary: | <p>Health impact analyses are increasingly tapping the broad spatial coverage of
satellite aerosol optical depth (AOD) products to estimate human exposure to
fine particulate matter (PM<span class="inline-formula"><sub>2.5</sub></span>). We use a forward geophysical approach
to derive ground-level PM<span class="inline-formula"><sub>2.5</sub></span> distributions from satellite AOD at
1 km<span class="inline-formula"><sup>2</sup></span> resolution for 2011 over the northeastern US by applying
relationships between surface PM<span class="inline-formula"><sub>2.5</sub></span> and column AOD (calculated offline
from speciated mass distributions) from a regional air quality model (CMAQ;
<span class="inline-formula">12×12</span> km<span class="inline-formula"><sup>2</sup></span> horizontal resolution). Seasonal average
satellite-derived PM<span class="inline-formula"><sub>2.5</sub></span> reveals more spatial detail and best captures
observed surface PM<span class="inline-formula"><sub>2.5</sub></span> levels during summer. At the daily scale,
however, satellite-derived PM<span class="inline-formula"><sub>2.5</sub></span> is not only subject to measurement
uncertainties from satellite instruments, but more importantly to
uncertainties in the relationship between surface PM<span class="inline-formula"><sub>2.5</sub></span> and column AOD.
Using 11 ground-based AOD measurements within 10 km of surface PM<span class="inline-formula"><sub>2.5</sub></span>
monitors, we show that uncertainties in modeled
PM<span class="inline-formula"><sub>2.5</sub>∕AOD</span> can explain more than 70 % of the spatial and
temporal variance in the total uncertainty in daily satellite-derived
PM<span class="inline-formula"><sub>2.5</sub></span> evaluated at PM<span class="inline-formula"><sub>2.5</sub></span> monitors. This finding implies that a
successful geophysical approach to deriving daily PM<span class="inline-formula"><sub>2.5</sub></span> from satellite
AOD requires model skill at capturing day-to-day variations in
PM<span class="inline-formula"><sub>2.5</sub>∕AOD</span> relationships. Overall, we estimate that
uncertainties in the modeled PM<span class="inline-formula"><sub>2.5</sub>∕AOD</span> lead to an error of
11 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span> in daily satellite-derived PM<span class="inline-formula"><sub>2.5</sub></span>, and
uncertainties in satellite AOD lead to an error of 8 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span>.
Using multi-platform ground, airborne, and radiosonde measurements, we show
that uncertainties of modeled PM<span class="inline-formula"><sub>2.5</sub>∕AOD</span> are mainly driven by
model uncertainties in aerosol column mass and speciation, while model
representation of relative humidity and aerosol vertical profile shape
contributes some systematic biases. The parameterization of aerosol optical
properties, which determines the mass extinction efficiency, also contributes
to random uncertainty, with the size distribution being the largest source of
uncertainty and hygroscopicity of inorganic salt the second largest. Future
efforts to reduce uncertainty in geophysical approaches to derive surface
PM<span class="inline-formula"><sub>2.5</sub></span> from satellite AOD would thus benefit from improving model
representation of aerosol vertical distribution and aerosol optical
properties, to narrow uncertainty in satellite-derived PM<span class="inline-formula"><sub>2.5</sub></span>.</p> |
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| ISSN: | 1680-7316 1680-7324 |