Summer is more than half over, and, thus far, it has been a very good one for air quality in the Chicago metropolitan area. By many measures, both June and July were among the cleanest on record, and August is off to a great start.
Of course, the area's relative hiatus from summer smog may or may not last through Labor Day, but the long-term trends point to continued improvements in the years ahead.
So far this summer, there has not been a single violation of the federal smog standard, even though it became much more stringent this year. Chicagoans have been breathing air as clean as that in remote regions—not bad for a city with nearly 3 million residents and chronic traffic congestion.
Luck has had much to do with it. Summer smog is created by two pollutants, nitrogen oxides (NOx) and volatile organic compounds (VOCs), in the presence of sunlight. Conditions conducive to smog formation—hot, cloudless, stagnant summer days that can really cook ambient NOx and VOC molecules into smog—have been unusually rare for the area over the past three months. What's been bad news for vacationers and air conditioner sellers has been good news for air quality.
But it isn't all luck. Emissions of NOx and VOCs have declined substantially in recent decades, and continue to go down each year. Motor vehicles are the single largest source of these smog precursors, and they have gotten significantly cleaner since the 1970s. Strict federal emission limits for cars and trucks have more than compensated for the area's recent population growth and increases in both number of vehicles and total miles traveled. Area power plants, factories and other businesses have also made a contribution by lowering emissions.
Given that Chicago was singled out as one of the nine smoggiest metropolitan areas in the country by the Environmental Protection Agency in 1990, the progress has been remarkable.
This trend will continue for the long term. New federal regulations, which will be phased in over the next few years, demand even greater reductions in smog-forming compounds from cars, SUVs and trucks. No additional measures need be imposed to achieve these improvements, just the inevitable turnover from older and dirtier vehicles to cleaner new ones. Tougher new utility emissions standards, one of which took effect this year, will also help bring down pollution levels. Over time, we will see less and less summer smog, regardless of the weather.
A hot, humid, and smoggy end to August may yet await us, but the unusually clean air of June and July will become more typical of future Chicago summers.