Quantitative Maps Describing Respirable Particle Episodes in the San Joaquin Valley Using Moderate Resolution Satellite Imagery

We describe the San Joaquin Valley of California as an example of several regions of where the use of kilometer-scale satellite aerosol optical thickness can indeed provide quantitative maps of episodic poor air quality (particulate matter) but only if (a) daily calibration of the AOT to particle relationship, and (b) a measure of vertical dilution, are used in concert. This valley is a large dry area under a strongly subsiding anticyclone and consequent very thin wintertime mixed layers, high but heterogeneous surface albedos, and also varied particle characteristics. There are also hard-to-quantify sources from domestic burning and spatially separated ammonia and nitrate precursors. Episode concentrations and dosages are required to better understand acute morbidity and mortality. Source-driven models are challenged by these difficulties. We estimate PM2.5 to within 7 µg m^-3rms error and with Rvalues of 0.89. based on remotely sensed MAIAC (Multi-Angle Implementation of Atmospheric Correction) observations using NASA's moderate resolution imagers. A sample map is shown with this abstract. We characterize mixed-layer dilution using column water vapor (CWV, otherwise "precipitable water"); 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.

We outline ideas for defining the best region for such PM2.5 mapping. and give a prospectus for extending the method to developed and developing countries, e.g., Italy, Israel, and India.