About 1 in 10 U.S. cities exceeds World Health Organization (WHO) standards for particulate air pollution (think smoke and soot). And, considering the state of affairs globally, that’s the good news for today.

Across Europe, according to WHO data released yesterday, three-in-five cities are above the health standards for particulates.  Among the handy examples are Paris and Rome; also London, which just elected a new mayor partly on his pledge to tighten controls on vehicle pollution in the English capital.

Europe’s continued reliance on diesel for vehicle fuel, rather than gasoline, is making particulate reductions more difficult. Still, the region is doing better than the global average – and way better than the world’s poorest countries.

In assessing 3,000 cities around the world, WHO found that 80 percent of their combined population was exposed to unhealthy particulate concentrations. In the lowest-income regions, that rose to 98 percent of the population; even in the wealthiest regions, more than half the population (56 percent) was breathing unhealthy air.

Note that these statistics may understate the situation, because WHO data concern only cities with populations larger than 100,000, where air quality is subject to official monitoring. Plenty of governments don’t bother with air quality monitoring, including most of those on the continent of Africa.

Still, data from 3,000 cities around the world were analyzed for Thursday’s report, almost double the number in the last update two years ago.

Looking back a little further, to 2008, WHO analysts found these notable trends:

• Urban air pollution levels increased by 8 percent globally.
• In the three regions where air pollution levels were highest overall—the Eastern Mediterranean, South-East Asia and western Pacific—air pollution increased by more than 5 percent in two-thirds of the cities.
• On the positive side, “More than half of the monitored cities in high-income countries and more than one-third in low- and middle-income countries reduced their air pollution levels by more than percent in five years.”

Looking at national patterns

WHO aggregates and reports its air-quality data on a regional rather than national basis, leaving it to journalists to look up country-by-country numbers.

Of the 10 world cities with the worst air quality, according to a chart prepared by the Wall Street Journal, four were in India, two each were in China and Saudi Arabia, with Iran and Cameroon rounding out the list. (New Delhi has left the list this time around, New Kerala reports with pride.)

I decided to peer at the 372 U.S. cities in the North American portion of the database and counted 37 that exceeded WHO standards.

None were in Minnesota. Most were in California, Pennsylvania, Ohio and my home state of Indiana, which I used to think of as agricultural, but has evolved into one of the most manufacturing-intense states in the nation.

I also noted that none of the 37 appear to be in violation of U.S. Environmental Protection Agency standards for particulates, because those limits are somewhat more liberal than WHO’s.

(For particles of 10 microns or smaller, known as PM 10, WHO considers 50 micrograms per cubic meter to be the upper limit for a 24-hour average; EPA draws the line at 150. For particles 2.5 microns and smaller, WHO’s standard is 25 micrograms and EPA’s is 35.)

A major driver of disease

Americans have come to associate particulate pollution with asthma and other respiratory disease — which is certainly correct — but the levels seen in other parts of the world cause myriad other complications, which, in WHO’s estimation, makes it “the world’s largest single environmental risk.”

In a report two years ago, WHO analysts that found about 7 million deaths per year could be traced to particulates and the diseases they drive, including heart disease, strokes, chronic obstructive pulmonary disease, lung cancer and – in small children – acute lower respiratory infections.

That’s about one-eighth of deaths from all causes, by the way.

Among these particulate-driven fatalities, slightly less than half (3.7 million) were associated with outdoor air pollution and slightly more than half (4.3 million) with bad air indoors.

Readers who are quick at math will notice that those numbers add to 8 million, not 7. That’s because about 1 million of the deaths are attributed to overlapping exposure to two types of bad air. But in much of the world developing world, where air pollution has less to do with gas- and diesel-powered vehicles than with burning wood, coal, crop residue, cattle dung and other “biomass” for cooking,  the distinction between ambient and household air quality is perhaps a bit academic.

Dr. Kirk Smith, a Professor of Global Environmental Health from the University of California at Berkeley, who began to measure the air pollution exposure from cooking over open biomass cook stoves in the 1970s, offered this observation on the WHO website:

“Having an open fire in your kitchen is like burning 400 cigarettes an hour. Unfortunately, we have not made a lot of progress in the past decades and household air pollution is still the largest single health risk factor for Indian women and girls.”

The World Health Organization portal on this research is here, and for those who want to skip straight to the cities and their ratings, an awfully big spreadsheet is waiting for you here.