Slide Show: Painting the Picture of Air Quality with Satellite Data
How satellite imagery combines with ground-based detectors to graphically render air quality--and how the U.S. government and the university-based Smog Blog get the news out
LASER DETECTION Time to time, Hoff's U.M.B.C. students fire up a laser to assist in their local air quality analyses. This LiDAR (light detection and ranging) system, housed at the Elastic LiDAR Facility (ELF) in Catonsville, Md., is similar to radar—but rather than radio waves, it uses a laser to record the distance to objects, in this case airborne particles, which reflect back signals. "Like radar is used to range and detect clouds and precipitation, LiDAR measures the distance to layers of smoke and haze aerosols over U.M.B.C.," Hoff says. "This helps identify [pollution] sources by using models of air motion." This image from U.M.B.C.'s LiDAR system captures aerosols passing over Baltimore on January 12, 2006.
UMBC/U.S. Air Quality Smog Blog
RED ALERT On July 18, 2008, high levels of ozone led to AQI code red in Baltimore and Philadelphia, with much of the Northeast bathed in ill air as well. Ozone is clear, so visible light satellite images did not reveal its presence, but people certainly took notice. "Breathing air with ozone in it can reduce lung function," says the EPA's Davis, because it causes inflammation. "Like a sunburn on your skin, [ozone] does that to your airways," she says. Ozone increases susceptibility to respiratory infections and distress, aggravates asthma sufferers' symptoms, and can in turn put people with cardiovascular issues in harm's way, all leading to upticks in doctor and emergency room visits, Davis says.
Environmentally, ozone can damage sensitive vegetation, reduce growth productivity, and leave plants prone to disease and pests. Given ozone's ability to do widespread harm, the EPA collects data from over 1,500 ozone detectors nationwide.
NASA/Google Earth/EPA/U.S. Air Quality Smog Blog
TELLTALE EMISSIONS In January 2008, the Smog Bloggers noticed a spike in nitrogen dioxide NO2 emissions over the Alberta in western Canada. They got this visual whiff of the EPA-tracked pollutant courtesy of the multitasking ozone monitoring instrument (OMI) on board NASA's Aura satellite. (The OMI is a collaborative contribution from the Netherland's Agency for Aerospace Programs, The Royal Netherlands Meteorological Institute, and the Finnish Meteorological Institute.) "Nitrogen dioxide is not generally high over northern latitudes in winter," U.M.B.C.'s Hoff says. This has led to speculation that the nitrogen dioxide is from natural gas flaring, as a result of fossil fuel drilling operations in oil-rich Alberta. "Some of our NOAA colleagues think that it might be slash burning of cut trees to make way for oil/gas operations," Hoff says, although he says that is speculative, as well. "We need some on-the-ground verification...it's sometimes a detective story piecing all these things together," he says.
In this image, high levels of NO2 emissions sprout from Mexico City, Denver, the vicinity of Minneapolis–Saint Paul, and along part of the Interstate 95 corridor that runs through northern Maryland and past Philadelphia.
KNMI/NASA/NIVR/ U.S. Air Quality Smog Blog
FLAMES FROM NEAR AND FAR Wildfires raging in northern California spew air pollution more than halfway across the continent in this National Oceanic & Atmospheric Administration (NOAA) Hazard Mapping System (HMS) image from July 11, 2008. Government analysts manually combine data from specialized meteorological satellites to create the HMS readout. A detected smoke plume, rendered a flat gray in this image, rises from red fires exaggerated in relative size in this long view to better indicate their location. The smoke from foreign fires can cast a long pall over the landscape: A few days earlier, on July 8, smoke and other particulates carried on the wind reached the U.S. from forest fires in Canada and as far as Russia, contributing to Northeast haze and blowing out over the Atlantic Ocean.
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LOOKING DOWN ON SMOG Although this satellite image does not have city and county demarcations, it's easy to pick out the general municipal limits of Los Angeles and its sprawling environs—they fall under the gray cloud of smog at the center of the image. Despite stringent air pollution laws, the second-largest city in the U.S. has some of the worst air quality in the nation. Car-clogged freeways and southern California's abundant sunshine help whip up the thick smog.
Despite a steady rise in U.S. population and more automobiles on the road, U.S. air quality has not suffered. "Air quality is definitely improving across the country and has been for some time," says the EPA's Davis. For example, between 1980 and 2007 the U.S. saw a 21 percent average decrease nationwide in ozone levels, she says. Fine particles, the smallest bits of particulate matter that contribute to haze, have dropped over 40 percent since 1980. U.M.B.C.'s Hoff credits tougher government regulations on power plant and car emissions for much of the improvement.
NASA/ U.S. Air Quality Smog Blog
THE VIEW FROM THE GROUND Los Angeles chokes under a blanket of smog. Though originally coined as a portmanteau of smoke and fog around 1900, modern smog often is neither; rather it is a hazy mixture of air pollutants—some man-made and others natural. A key ingredient: volatile organic compounds (VOCs). These are emitted by industrial chemicals and when people fill their tanks with gasoline, for instance, though some trees emit VOCs, as well, the EPA says. Another smog-maker is nitrogen dioxide from sources including vehicle exhausts and power plant emissions. In the presence of heat and sunlight, these compounds can form ozone, a colorless gas that consists of three oxygen atoms. In the stratosphere this molecule deflects much of the sun's harmful ultraviolet radiation, but at ground level ozone can make breathing difficult; it also blights plant leaves and is a greenhouse gas. Smog also contains particulate matter, which consists of microscopic bits suspended in air that run the gamut from aerosolized liquids and metals to plant pollen and dust kicked up by wind and automobiles.
EAST COAST TOAST: True-color shots from NASA's Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite overlaid with
Google Earth maps show the haze and smoke from the Evans Road fire in North Carolina on June 13, 2008, U.M.B.C.'s Hoff says. The smoke stretches northward through Virginia toward Washington, D.C.
The color of the dots on the map correspond to the EPA's Air Quality Index (AQI), the system of categorizing relative air quality. The four AQI color categories, sometimes called codes, seen here include green (good), yellow (moderate), orange (unhealthy for sensitive groups—meaning children, the elderly and those with respiratory ailments), and red (unhealthy for all). The scale also has two extreme categories: purple, and rarely seen maroon, which only comes up in forest fire situations, says Alison Davis, a senior adviser for public affairs at EPA's Office of Air Quality Planning & Standards. See the EPA-led interagency AIRNow Web site for more details on the AQI. NASA/Google Earth/EPA/U.S. Air Quality Smog Blog Advertisement