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Discussion papers
https://doi.org/10.5194/acp-2019-262
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-262
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 19 Aug 2019

Submitted as: research article | 19 Aug 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Satellite Mapping of PM2.5 Episodes in the Wintertime San Joaquin Valley: A "Static" Model Using Column Water Vapor

Robert B. Chatfield1, Meytar Sorek-Hamer1,2, Robert F. Esswein3, and Alexei Lyapustin4 Robert B. Chatfield et al.
  • 1NASA Ames Research Center, Moffett Field, CA 94035, USA
  • 2Universities Space Research Association, Moffett Field, CA, USA
  • 3Bay Area Environmental Institute, Moffett Field, CA, USA
  • 4NASA Goddard Space Flight Center, MD, USA

Abstract. The use of satellite Aerosol Optical Thickness (AOT) from imaging spectrometers has been successful in quantifying and mapping high PM2.5 (particulate matter mass < 2.5 µm diameter) episodes for pollution abatement and health studies. However, some regions have high PM2.5 but poor estimation success. The challenges in using Aerosol Optical Thickness (AOT) from imaging spectrometers to characterize PM2.5 worldwide was especially evident in the wintertime San Joaquin Valley (SJV). The SJV's attendant difficulties of high-albedo surfaces and very shallow, variable vertical mixing also occur in other significantly polluted regions around the world. We report on more accurate PM2.5 maps for the whole-winter period in the SJV, Nov 14, 2012–Dec 11, 2013. Intensive measurements by including NASA aircraft were made for several weeks in that winter, the DISCOVER-AQ California mission.

We found success with a relatively simple method based on calibration and checking with surface monitors and a characterization of vertical mixing, and incorporating specific understandings of the region's climatology. We estimate PM2.5 to within ~ 7 µg m–3 RMSE and with R values of ~ 0.9, based on remotely sensed MAIAC (Multi-Angle Implementation of Atmospheric Correction) observations, and that certain further work will improve that accuracy. Mapping is at 1 km resolution. This allows a time sequence of mapped aerosols at 1 km for cloud-free days. We describe our technique as a "static estimation". Estimation procedures like this one, not dependent on well-mapped source strengths or on transport error, should help full source-driven simulations by deconstructing processes. They also provide a rapid method to create a long-term climatology.

Essential features of the technique are (a) daily calibration of the AOT to PM2.5 using available surface monitors, and (b) characterization of mixed-layer dilution using column water vapor (CWV, otherwise "precipitable water"). We noted that on multi-day timescales both water vapor and particles share near-surface sources and both fall to very low values with altitude; indeed, both are largely removed by precipitation. The existence of layers of H2O or aerosol not within the mixed layer adds complexity, but mixed-effects statistical regression captures essential proportionality of PM2.5 and the ratio variable (AOT/CWV). Accuracy is much higher than previous statistical models, and can be extended to the whole Aqua-satellite data record. The maps and time-series we show suggest a repeated pattern for large valleys like the SJV — progressive stabilization of the mixing height after frontal passages: PM2.5 is somewhat more determined by day-by-day changes in mixing than it is by the progressive accumulation of pollutants (revealed as increasing AOT).

Robert B. Chatfield et al.
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Status: open (until 14 Oct 2019)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Short summary
There is a great need to define health-affecting pollution by small particles "respirable aerosol". The wintertime San Joaquin Valley experiences severe episodes that need full maps. A few air pollution monitors are set out by agencies in such regions. Satellite data on haziness and daily calibration using the monitors map out improved pollution estimates for the winter 2012–2013. These show patterns of valuable empirical information about sources, transport, and cleanout of pollution.
There is a great need to define health-affecting pollution by small particles "respirable...
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