U.S. Air Quality

Special Feature: Air pollutants in South Africa and the need for more 'eyes'

The more than 70 government delegations at the GEO IV Plenary Meeting are preparing for Friday's Ministerial summit, but we here at the "Smog Blog" hope they have a chance to enjoy the atmosphere of Cape Town, which looks beautiful from all the Earth observing sensors. Our special coverage of South Africa continues today with a multi-sensor review of Thursday's air quality in South Africa and Cape Town, and the need to develop the capacity for many more 'eyes' to observe the air we breathe.

The NASA MODIS sensor on the Terra satellite showed a few clouds Thursday morning over western South Africa (left image). By afternoon, when the MODIS sensor on the Aqua satellite flew over, the clouds had turned to storms in the north-central part of the country (right image). All day though, it continued clear and sunny over Cape Town. The SCIAMACHY UV index was 11 again Thursday in Cape Town, an indicator of extreme risk of harm from unprotected sun exposure. (The UV index was 12.3 in Durban, South Africa, and 15 in some of the other southern African countries.)

For Cape Town, we can look at a couple of on-the-ground sensors. Sometimes a sensor as simple as a webcam can tell us about visibility. On the left is an image from the Cape Town web cam, showing those sunny skies with a little light haze. More quantitatively, the City of Cape Town again kindly shared their PM10 monitoring data with us for Thursday. (PM10 is a measure of particles in the air that are less than 10 microns in diameter; the 24-hour average health standard for PM10 is 50 micrograms per cubic meter (ug/m3).) The time series graph from the Waterfront and Khayelitsha monitors again shows significant peaks (right), likely due to cars, shipping, road dust, and local emissions.

(Please note that these data are preliminary "live data" that have not been validated and that the standard is an average of these points, not any single value).

EUMETSAT is a weather satellite, but it does have an algorithm that can detect dust. The dust image of southwest South Africa is a little hard to interpret, but the pink/majenta color indicates dust. It does show higher levels off the coast of Cape Town, so perhaps some of the increased PM10 is dust, as well as industrial and roadway pollution.

With satellite sensors, we can get some perspective on other air pollutants especially in areas where we don't have ground-based monitors. ESA/KNMI's Tropospheric Emission Monitoring Internet Service (TEMIS) provides some near real-time data from the NASA/ESA Ozone Monitoring Instrument (OMI). The OMI sensor provides SO2 data that works best for high concentrations from volcanos and large industry. So it is interesting that on Thursday there were some increased levels of SO2 in spots near Johannesburg and in the central part of the country (left image). A portion of this region was declared an air pollution hot spot this week by the South Africa Environmental Affairs and Tourism Ministry, due to high levels of pollutants from industry and agriculture. The NO2 levels, also from OMI, were high in the same area (right image). The MODIS true color image of eastern South Africa showed clouds and several small smoke plumes likely from wildfires.

In this assessment, we used 8 satellite and ground-sensors, reviewed about 20 websites, and received and processed data directly from the city, in order to just begin to review the air quality of all of South Africa, over 1.2 million square km. (And there are many other sources of data available retrospectively that have not been included!) It took about 3 hours for this review for just this one location and one day with a subset of information. Obviously, one set of eyes cannot possibly use all the wonderful monitoring resources being launched and deployed, and one person located thousands of miles away cannot know about the local industry, terrain, traffic, weather, and other factors important in understanding air quality. So, we need to develop the capacity of many more human 'eyes' everywhere to use Earth monitoring data to observe our atmosphere and the world. We are working with the SERVIR project to transfer the Smog Blog and the skills to interpret air quality data to Central America. We hope we can take many more small steps to build and connect the global air quality community in order to better understand air pollution, its causes, and the ways to create clean air for everyone.

Posted by Jill Engel-Cox at November 29, 2007 8:10 PM | TrackBack