A huge, destructive hurricane takes aim at a major U.S. city. The media creates a riveting drama, followed by millions of people, who watch in awe as the massive storm smashes ashore. Grimly, wind-blown reporters and concerned news anchors document the mounting death toll and billions in damage wrought, bemoaning nature's deadliest and most destructive weather phenomena--the hurricane.
We've got it all wrong. The hurricane is not nature's deadliest and most destructive weather phenomena. Yes, hurricanes have taken a terrible toll in the U.S. over the past 20 years. They've killed an average of 150 people and caused $15 billion in damage per year--mostly thanks to Katrina. But the nation's deadliest weather events are not destructive storms that shred cities. Nature's most innocent weather--high pressure systems that bring sunny skies and light winds--are our deadliest weather events, thanks to the witch's brew of pollution we pour into our atmosphere.
Figure 1. Pick your poison--a Category 5 hurricane, or a sunny high pressure system with light winds? If you're an asthmatic, or have heart or lung disease, you'd probably be better off picking the Cat 5 hurricane. Photo of Los Angeles smog courtesy of wunderphotographer boytonbeachboy.
How high pressure systems trap pollution
High pressure systems are regions where the air gradually sinks, warming as it approaches the surface. This warming, sinking air creates a layer of air aloft (typically near 3000 feet in altitude) that is warmer than the air beneath it. This "upper air inversion" acts as a lid on the atmosphere, keeping pollutants trapped near the surface. Updrafts carrying surface air into the inversion suddenly encounter air that is warmer and less dense, so the updraft dies and the pollutants that they were trying to carry aloft settle back down towards the surface. If the high pressure region is large, an extensive area of light winds at the surface will exist, keeping the pollutants trapped under the inversion from being blown away horizontally. If the high pressure system stays in place for several days, pollutants will accumulate day by day, reaching levels harmful to human health and triggering a sharp rise in the death rate. "Particulate matter," also known as particle pollution or PM, is the pollutant that causes the largest rise in the death rate. Particulate matter pollution can occur any time of year, when winds are light and an inversion exists. In summertime, a double-whammy dose of ozone pollution can also hit, if temperatures are warm enough to drive the chemical reactions that form ozone.
How many people does pollution kill?
Why is it that air pollution episodes that kill thousands of Americans don't receive the media attention that hurricanes get? It's because it is not obvious when someone dies from air pollution, and there is very large uncertainty in the numbers. The only way to see air pollution deaths is to analyze death rate statistics for multiple years, carefully filtering out other influences such as weather extremes. Over two thousand studies have been published in the scientific literature documenting the link between air pollution and higher death and hospitalization rates. Most of these studies concern fine particulate matter (less than 2.5 microns in diameter), which can get deep into a person's lungs and be passed into the blood stream. Recent studies have also documented higher death rates from ozone pollution. For example, in a 2004 study published in the Journal of the American Medical Association, Dr. Michelle Bell, an air quality and health expert at Yale University, found that an ozone increase of 10 parts per billion increased the death rate by an average of .52% in 95 U.S. cities (containing 40% of the U.S. population) during the period 1987-2000. Bell's research implies that a change in the ozone standard from the current 80 ppb (parts per billion) to the newly proposed standard of 60 ppb could prevent nearly 8,000 premature deaths per year in those 95 cities. About half of the people who died prematurely in Bell's study were over age 75, but the death rate increased the same amount for both young and old. In some cases, the people who died were victims of strokes or heart attacks that had other contributing causes, such as high blood pressure or sedentary lifestyles. Thus, the "premature deaths" caused by air pollution are only partly attributable to breathing bad air, while drowning in a hurricane's storm surge is entirely due to the hurricane. Nevertheless, a great many children die of pollution-induced asthma attacks who would not have died otherwise, and the mortality due to air pollution in the general population is in the thousands or ten of thousands each year. Outdoor air pollution in the U.S. due to particulate pollution alone was estimated by the EPA in 1997 to cause at least 20,000 premature deaths each year. A 2005 study by EPA scientists (Particulate Matter Health Risk Assessment for Selected Urban Areas) estimated that over 4,700 premature deaths occur each year in just nine cities (Detroit, Los Angeles, Philadelphia, Pittsburgh, St. Louis, Boston, Phoenix, Seattle, and San Jose)--even if those cities all met the current federal standards for particulate matter pollution. Extrapolating these data to the entire nation puts the annual death toll in the tens of thousands--but the EPA has not calculated that total. Some studies have placed the annual pollution death toll in the U.S. at 50,000 to 100,000 (Dockery, D.W., and C.A Pope III. Acute Respiratory Effects of Particulate Air Pollution. Annual Review Public Health, 1994, vol. 15,107-32.) The death toll is much higher in other parts of the world, where air pollution standards are not as stringent (see the photos below of pollution in Cairo and Hong Hong!) Globally, about 800,000 people per year die prematurely due to outdoor air pollution, according to a 2005 study published in the Journal of Toxicology and Environmental Health. This represents about 1.2 percent of total annual global deaths.
Figure 2. Trends in fine particulate air pollution in the U.S. Since 1999, fine particles (less than 2.5 micrometers in diameter) have decreased 15%. Image credit: U.S. EPA.
Progress is being made
Significant progress has been made in recent years in cleaning the nation's air. Between 1970 and 2004, total emissions of the six major air pollutants regulated by the Environmental Protection Agency (EPA) dropped by 54 percent. This is particularly impressive when noting that the gross domestic product increased 187 percent, energy consumption increased 47 percent, and U.S. population grew by 40 percent during the same time. Fine particulate matter pollution, which causes the most deaths due to pollution, has dropped 15% since 1999 (Figure 2), although it did increase in some Eastern U.S. cities in 2006. In March 2005, the EPA instituted the Clean Air Interstate Rule (CAIR). This new rule will cost $3 billion per year to implement, but the EPA estimates annual savings of nearly $100 billion in health costs, plus the prevention of over 17,000 premature deaths, by the year 2015.
How you can avoid a premature death due to air pollution
- Pay attention to forecasts for high air pollution days to know when to take precautions
- Avoid exercising near high-traffic areas
- Avoid exercising outdoors when pollution levels are high, or substitute an activity that requires less exertion
- Eliminate indoor smoking
- Reduce the use of fireplaces and wood burning stoves
How you can help others avoid a premature death due to air pollution
- Support national, state and local efforts to clean up sources of pollution. When one hears talk about the high cost of cutting fossil fuels use to reduce global warming, keep in mind that any lessening of fossil fuel use will also reduce air pollution and all of its costs.
- Conserve electricity and set your air conditioner at a higher temperature.
- Choose a cleaner commute--share a ride to work or use public transportation. Combine errands and reduce trips.
- Bicycle or walk to errands when possible.
- Refuel cars and trucks after dusk.
- Limit engine idling.
- Get regular engine tune ups and car maintenance checks (especially for the spark plugs).
- Avoid spilling gas and don't "top off" the tank. Replace gas tank cap tightly.
- Properly dispose of household paints, solvents and pesticides. Store these materials in airtight containers.
- Paint with a brush, not a sprayer.
- Buy low VOC paints for indoor and outdoor painting jobs.
- Reduce or eliminate fireplace and wood stove use.
- Avoid using gas-powered lawn and garden equipment.
- Avoid burning leaves, trash and other materials.
- Use household, workshop, and garden chemicals in ways that keep evaporation to a minimum, or try to delay using them when poor air quality is forecast.
- Replace your car's air filter and oil regularly
For more information
The U.S. Environmental Protection Agency (EPA) has designated this week as Air Pollution Awareness Week. Check out their Air Pollution Awareness Week web site to learn more.
My next blog will be Monday.
Hong Kong skyline through mist and pollution, as seen from "The Peak" park. South-East China.
This is a picture of the Pyramids at Giza taken from Cairo Tower at sunset. It highlights the pollution problem in Cairo.