As another Earth Day approaches, many Americans believe air quality is getting steadily worse, particularly in California, just like the rest of the environment. The most recent air--quality data presents a different picture.

The past three years have seen the nation's lowest levels of ozone smog since monitoring began in the early 19708. In 2004, ozone levels were the lowest in U.S. history. In 2005, a hot summer caused more exceedences of the Clean Air Act standard than were experienced in 2004. Ozone levels, however, remained below those of previous summers with above-average temperatures, especially 1988 and 1998.

As the media noted, Houston and the San Joaquin Valley experienced "exceptionally clean air." While that made Los Angeles look bad by comparison, California's largest city did well on its own terms, with fewer exceedences of the ozone standard in 2005 than in 2004, part of a long term trend.

In 1975 Los Angeles experienced 192 exceedences of the one-hour ozone standard, down to 27 last year. Exceedences of the tougher eight hour standardfeJl from 201 in 1975 to 75 last year. These trends understate actual conditions.

'I'here are dozens of ozone m0nitors in the Los Angeles air basin. But an exceedence at only one, according the rules of the Environmental Protection Agency (EPA), applies to the entire LA. basin. In large areas of the L.A. air basin there have been no exceedences of the ozone standard at aU for several years. Practically speaking, millions of residents have had no exposure to high levels of ozone. The EPA is even taking note of this fact with changes to its reporting language.

Progress on ozone, it should be noted, was not limited to Los Angeles. In the Washington. D.C., area, not a single "Code Red" day for poor quality was declared over the summer, despite hot temperatures. Ozone levels are falling in 19 Eastern states, and nitrogen oxide emissions have fallen by 50 percent since the year 2000.

The California Air Resources Board (CARB) shows that hydrocarbons, the main component of volatile organic compounds, or VOCs, have fallen 99.3 percent since the 1960s. Similar trends follow for tailpipe emissions, down 96 percent since the 1960s. These emission rates per mile apply to all makes and models unifprmly. It is not true that, as USA Today claimed in 2003, Americans are "driving vehicles that give off more pollution than they did in the 1980s. " They aren't.

According to the EPA, VOCs from cars and trucks have declined by 78.8 percent since 1970, and carbon monoxide emissions trom cars are down 64 percent. During this time the total number of cars and trucks in the United States more than doubled, and the total miles driven increased 181 percent.

Only reporting that bears a grudge against facts can charge that cars pollute more now than during tile 198Os.

Both the California Air Resources Board and the EPA forecast that emissions from autos win fall another 75 to 80 percent from current levels. In 1980, emissions from cars and trucks accounted for a third or more of total VOC emissions. CARB estimates, that by 2020, mobile source emissions will only account for five percent of total VOC emissions.

Reductions in VOC emissions from mobile sources account for a full two-thirds of the total reduction in VOC emissions achieved so far. Automobile emissions have fallen so far that, in 2005, it was announced that cattle are now a larger source of VOCs than cars in California's Central Valley.

The San Joaquin Valley Air Pollution Control District estimates that the average dairy cow emits 19.3 pounds ofVOCs a year. The valley 'has about 2.5 million dairy cows, which implies a staggering amount of VOCs not previously accounted for. The estimates, however, are disputed, and it remains unclear what kind of catalytic conventer could be applied to cows.

California's Central Valley is also home to more than 100 wineries, now coming to the attention of regulators as another source of volatile organic compounds. According to new estimates, these wineries emit almost 800 tons of VOCs a year, more than the auto fleet. The wine industry is concerned that the kind of emissions-control technology used in the chemical and refining industry can't be applied to fermentation wilmout damaging the wine.

Californians may want to stock up, but there is another side to increased regulatory attention on the agricultural sector. Regulators are moving to more diffuse and smallscale sources of emissions PS the large technological fixes have begun to run their course.

That means those fixes are working and that the facts promote optimism, not gloom. There will always be room for improvement, but air quality is better in California than it was in 1970. If current trends continue, next Earth Day will be better still.

K. Lloyd Billingsley is editorial director at the California-based Pacific Research Institute. he can be reached at lbillingsley@pacificresearch.org.