Australian Bush Fires and local air quality
Particulate matter (PM) air quality information is usually derived from ground based instruments. These measurements, while valuable, are not well suited to provide air quality information over large spatial scales. In this study, using four years of satellite aerosol optical thickness at 0.55 mm (AOT) data derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra and Aqua satellites, we present multi year air analysis of PM air quality over Sydney, Australia. We then compare the satellite data with PM2.5 mass concentration measurements from six ground based stations in the area.
Our results indicate significant diurnal variations and an overall increase in PM2.5 during Southern Hemisphere spring and summer seasons due to bush fires. The air quality in Sydney, Australia is good throughout the year except during major bushfires when PM2.5 mass loading can increase from normal (<20 ?gm-3) to unhealthy conditions (> 70 ?gm-3). The satellite data also shows corresponding AOT changes from less than 0.1 to greater than 1.0 during bushfire events. We conclude that satellite data is an excellent tool for studying PM air quality over large areas, especially when ground measurements are not available. While this is the first multi-year combined satellite and ground-based air quality analysis over Sydney, ancillary information from lidars, sun-photometers, and size resolved chemistry measurements will further enhance our capability to monitor and forecast air quality in and around Sydney.
Figure 1. Bush fires in Sydney and surrounding area as observed from space. Top panels show Terra-MODIS three band true color images before, during and after major bush fires. Bottom panels are aerosol optical thickness retrievals that are an indicator of particulate matter air quality. The bars in the bottom panel indicate PM2.5 [PM2.5 ?gm-3 = Length of Bar (degree)*50] data reported from ground measurements. The air quality categories are color coded based on regression relationship between MODIS AOT and PM2.5 mass.
Figure 2. Effect of a major bushfires on air quality in Sydney during December 2001 and January 2002. Weekly mean values from six locations before, during and after bushfire events. a) PM2.5 mass concentration measured at ground b) Columnar AOT measured from MODIS. The horizontal lines in panel (a) show boundaries of air quality categories.
Reference
Gupta P., S. A. Christopher, M.A. Box, and G.P. Box, Multi year satellite remote sensing of particulate matter air quality over Sydney, Australia, International J. Remote Sensing, doi:10.1080/01431160701241738, 2007.
Radhi, M., M. A. Box, G. P. Box, P. Gupta, S. A. Christopher, Evolution of the Optical Properties of BIomass Burning Aerosol During the 2003 South-eastern Australian Bushfires, Applied Optics, 48 (9), pp. 1764-1773, doi:10.1364/AO.48.001764, 2009.