The Clean Air Act comes up for reauthorization this year in what some might consider a hostile environment. The costs associated with it are surely going to be the focus of upcoming congressional hearings -- and the costs are not insignificant. The Council on Environmental Quality recently estimated that air pollution control cost more than $22 billion in 1979 and that cumulative costs would reach about $300 billion by 1988 -- even if there were no inflation.

But are we spending these funds in a cost-effective manner?

Efforts to control air pollution are directed primarily at achieving federal standars for air quality outdoors. These standards were set by the Environmental Protection Agency chiefly to protect public health. Yet, most people spend 90 to 95 percent of each day indoors, so their total exposure to air pollutants is largely determined by pollution inside the home and work place.

Now that energy-efficient buildings are becoming more prevalent, the problem is likely to get worse. Energy conservation measures often call for reduced air flow between the indoors and the outdoors. Other things being equal, sealed-up homes can be expected to trap pollutants -- both conventional pollutants and the more exotic ones (formaldehyde and radioactie radon, for example) that we are only now hearing about. So an effective strategy to reduce total air pollution exposure must look much more closely at the indoor environment.

In this context, two specific air pollutants present interesting aspects of the regulatory problem: nitrogen dioxide (NO2) and carbon monoxide (CO). As suggested in a recent Post editorial and confirmed by my own research, there are lingering questions about whether these two air pollutants do in fact pose serious, long-term health threats at concentrations near current standards. Nevertheless, the nation is currently spending billions of dollars each year to control NO2 and CO emitted by both stationary sources (such as factories and power plants) and mobile sources (principally automobiles). Furthermore, EPA has proposed an even more stringent one-hour (outdoor) CO standard and hs been considering adding a new one-hour NO2 standard to the existing annual standard. Without taking into consideration the indoor environment, such proposals may not be sound regulatory policy.

Studies have indicated that indoor levels of both nitrogen dioxide and carbon monoxide can easily exceed allowed concentrations outdoors. A major indoor source of these pollutants is gas cooking. Even without turning on a gas stove, significant amounts of NO2 and CO are emitted from pilot lights unless the stove is equipped with automatic (electrically ignited) pilots. During and after cooking, levels are even higher. In one study, NO2 levels during cooking were five times higher than the federal outdoor standard. In another study involving nine different kitchens, CO levels after 20 minutes of cooking exceeded the outdoor one-hour standard in all cases but one. Even more striking is the fact that the elevated levels of these pollutants can persist for hours after cooking has ceased, and the concentrations can diffuse quickly throughout the house.

How widespread are these exposures? And how could they be reduced? According to the Census of Housing, 50 percent of American homes were equipped for gas cooking in 1977. Thus, a potential problem exist in as many as 38 million homes. The use of stove hoods and fans (vented to the outside) or even an open window can reduce NO2 and CO concentrations.

For even more significant decreases, adequate cross-ventilation is necessary. Unfortunately, the lack of emphasis on the indoor environment has meant that data is scarce concerning the number of control devices in existence, the frequency with which control measures are used and, most important, the effectiveness of such controls in reducing exposures.

Whether or not the exposures to these pollutants constitute a serious danger to public health, crude information suggests that reducing indoor air pollution may be far cheaper than obtaining the same effect by controlling the outside environment. In the case of unvented gas ranges, data suggest that the cost of retrofitting is approximately $200 if the unit is located near or on an exterior wall. (In other locations, costs would presumably be higher.)

The point is not that the federal government should immediately mandate "a range hood and fan in every kitchen." Rather, it is that such control options should be carefully exmained as part of the normal decision-making process in regulating NO2 and CO -- especially since the government has advocated other costly programs to reduce outdoor exposures to these same pollutants.

And NO2 and CO are not the only examples that highlight the relevance of accounting for the indoor environment indeveloping more cost-effective air pollution regulations. There is now a fairly strong consensus that is is small particles -- the so-called "respirable particulates" -- that pose the most serious health threat. However, current federal standards are framed in terms of total (all-size) particulates.

If particulte standards were eventually revised to focus on these smaller, more damaging particles, the importance of indoor exposures must be considered or the result could be meaningless regulation. Smoking and cooking emit many of these tiny particles. Studies have shown that repeated indoor exposures to cigarette smoke impose air pollution burdens on non-smokers that exceed the federal outdoor standard for total particulates. Attempting to protect the public health solely by controlling exposures to respirable particles in the outside environment would not only be prohibitively expensive, but also unlikely to succeed.

The question is whether the indoor-outdoor problem will be taken into account in the administration's proposal for reauthorization of the Clean Air Act or in the debate that is likely to follow. Some parts of the federal government are aware of the problem -- there is an interagency research group on indoor air quality, an EPA-sponsored National Academy of Sciences study on indoor air pollution, a Department of Energy research program on residential air quality and a recent report by the General Accounting Office suggesting that the Clean Air Act be amended to mandate EPA responsibility in the indoor area. But unless air pollution policy-making takes account of the total exposure picture, it seems unlikely that we can obtain the "biggest bank from our regulatory bucks."