Objectives:
1. Gas Stoves
Most American homes rely on gas stoves. By itself, this does not necessarily translate into an indoor air problem. However, a survey in New York City found that half the population used gas stoves for supplemental heating (turning on the stove to warm the house or apartment).This habit translates into increased exposures.
What kind of exposures? Incomplete combustion releases hydrocarbons and carbon monoxide. Furthermore, combustion releases nitrogen oxides. Depending on other conditions, particulate exposures can be significant, too.
Simple dispersion usually reduces the pollutants within an hour, but ventilation techniques are critical. In one experiment, investigators installed a new stove and turned two burners on full for 35 minutes. With a standard ventilation fan above the stove, there was no significant problem. However, when the fan was not turn on, levels reached 2/3 of the federal standards for carbon monoxide. This is assuming no outdoor air pollution.
The lessons are simple: 1) keep equipment in good repair, 2) do not use it in inappropriate ways, and 3) turn on the fan.
2. Home heating
Most American homes use natural gas for heating. Usually, it is centralized heating with external venting, and therefore poses no significant indoor air problem. However, many problems can arise with the use of portable "space heaters." Improperly vented, they can be significant sources of carbon monoxide and nitrogen oxides. Kerosene heaters (normally reserved for outdoor use) can release the same pollutants along with sulfur oxides.
Even the traditional fireplace can be a significant source. Ever curl up by the fireplace and, as time passes, start to feel relaxed and maybe a little sleepy? It could be initial symptoms of carbon monoxide exposure! If it is followed by a headache, the evidence is even stronger.
Of course, I am not suggesting we ban fireplaces or all space heaters. However, simple recognition of sources followed by common sense application of controls (such as ventilation) can be our most important tools in controlling indoor air pollution.
The Clean Air Act was passed in 1963, originally as a guide to states. Federal involvement at that time was limited (remember, the EPA had not been established yet). Major amendments to the act were passed in 1970, 1977, and 1990, giving much more authority to the EPA.
A starting point to understanding the law is to review two philosophies regarding standards: best available technology, and air quality management. Best available technology is essentially focused on emission standards. That is, it centers on the emissions from an individual stack or tailpipe. By contrast, air quality management is focused on ambient standards. That is, it looks at the resulting quality of the actual ambient air that we breathe (i.e., we don't usually breathe directly from the tailpipe!).
Both standards are important, of course, but we have long recognized that since secondary air pollutants are created in the atmosphere, it is not enough to study just the primary emission sources. In other words, we need to understand the entire life cycle of air pollution. Over time, we have had a greatly improved understanding of the influence of individual emission sources on the resulting ambient air quality.
The Clean Air Act mandates the following programs:
State Implementation Plans are required from each state and overseen by EPA. Such plans also recognize air quality control regions (about 247 of them in the U.S., including our own South Coast AQMD in Los Angeles). Each region is classified in one of three ways:
attainment areas, where air quality has been attained, and is subject to no additional requirements;
non-attainment areas: where ambient air standards have not been attained, and therefore are required to take additional actions.
prevention of significant deterioration (PSD), where stricter standards are applied for special areas, divided into three classes (e.g., class 1 is for national parks).
National Ambient Air Quality Standards (NAAQS) address maximum permissable concentrations for criteria pollutants. Two types of standards can be used, each without regard to cost: 1) primary standards, which protects human health; and 2) secondary standards, which protects buildings, crops, water, etc. Notice that the use of "primary" and "secondary" here is different than the way we've used it before.
To assist the public in understanding these standards, the pollutant standards index (PSI) was developed as a uniform method to measure air quality, and covers five of the criteria pollutants: PM-10, SO2, CO, O3, NO2. Basically a zero means no pollutants and 100 means 100% of the allowable exposure. Anything above 100 would be a violation of the standard.
Three other major programs under the Clean Air Act include:
Health Effects of Criteria Air Pollutants
COPD is an acronym for "chronic obstructive pulmonary disease," which includes asthma, bronchitis, emphysema, and lung cancer. Whenever reference is made to "unhealthful for sensitive persons," this includes the very young, the very old, and the very sick. The very sick, in this case, includes individuals with COPD. This is critical to understanding the effects of the criteria pollutants.
Sulfur Oxides are primarily an irritant. They irritate the eyes as well as the lungs. Epidemiologically, they have the strongest association with mortality, especially among high risk populations (the very young, the very old, and the very sick). In other words, SOx aggravates existing health conditions with consequences on mortality rates.
Particulates are also respiratory irritants, and also have a strong association with increased mortality. In addition, they are synergistic with other contaminants, particularly sulfur oxides. Also, we should remember that depending on their chemical identity, particulates may be associated with cancers (e.g., asbestos, berrylium, organics).
Carbon Monoxide is an asphyxiant, meaning that it interferes with the transport of oxygen by hemoglobin in red blood cells. Together, they form carboxyhemoglobin, which cannot carry oxygen. Acute effects are centered in the heart and brain.
Ozone is associated with dryness of throat, and aggravates existing respiratory symptoms. It also decreases resistance to infections. However, ozone is subject to tolerance, which means that after living in an area with ozone, people can be subjected to larger concentrations and not be as affected.
Nitrogen Oxides have similar effects as ozone (you recall that it helps create ozone), but it is roughly 10 times less toxic than ozone. Like ozone, it decreases resistance , which is why associations have been found between photochemical smog and the incidence of respiratory illness.
Lead can be found in a multitude of sources (not just air) and has a long list of health effects. The major effects include anemia, kidney damage, and effects on the central nervous system.
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