Associated Press

Last week I wrote about the global environmental impact of rising coal exports to China. Sea shipments of thermal coal, used for heating and electricity generation, are skyrocketing, undermining attempts to tamp down the growth of global greenhouse gas emissions.

But there are also immediate tangible effects in terms of local pollution –- and nowhere more so than in China itself. Last week, just after Beijing’s mostly coal-fired heating system kicked in for the winter, the pollution became what an official Twitter account of the United States Embassy in Beijing briefly referred to as “crazy bad.”

Since last year, the United States Embassy has been issuing hourly Twitter updates on Beijing’s air quality, and some of the readings have been pretty shocking. The tweet emerged last week when levels of tiny particulate matter (known as PM 2.5) rose to over 500 micrograms per meter cubed. That’s about 20 times the limit that the World Health Organization regards as “acceptable and achievable” for a 24-hour period.

To protect public health, the United States Environmental Protection Agency sets the goal for the average annual concentration at 15 micrograms per meter cubed, and the 24-hour average at 35 micrograms per meter cubed.

The tiny PM 2.5 particulates travel deep into the lungs and are associated with lung disease, heart disease and cancer. (A nice summary of the risks is here.) PM 2.5 are created not just by burning coal but also by burning other fossil fuels and by things like car exhaust and construction dust.

“Crazy bad” is not part of the United States Embassy’s official air quality rating system, and the embassy quickly adjusted its assessment to a more scientific (and diplomatic) “beyond index.”

As a reporter for this newspaper, I enjoyed living in Beijing from 1997 to 2003, but “crazy bad” sometimes seemed like an apt description of air quality. On some days, we couldn’t see the ground from our 11th-floor apartment, and the sun in Beijing was often a glowing disk behind the pollution. My young son suffered bouts of asthma, bronchitis and pneumonia, problems that disappeared when we moved away.

We didn’t have the information in the embassy’s tweets then. (The embassy reportedly installed the necessary air monitoring equipment last year.) The embassy’s precise measurements do provide more specific — and worrisome — information than Beijing’s system of reporting the number of “blue sky days.”

By all accounts, Beijing took great pains to improve air quality in the lead-up to the 2008 Summer Olympics, and we all remember the beautiful blue skies we saw on TV. But since last year, China has been a large coal importer. And as it buys up the world’s coal and burns it, could it be slipping back?

How to minimize the pollution that goes with rapid economic development? What are the health consequences for China’s citizens of being exposed to such high levels of particulates? China’s leaders live in Beijing, just as many of their children and grandchildren presumably do. I wonder what they think about that.