Today's date:
Fall 2006

We Are Breathing Chinese Pollution

Steven Cliff is an atmospheric scientist at the University of California, Davis.

Davis, California — Expanding deserts, coal-fired growth and auto emissions in China are not only threats to the health and well-being of the Chinese, but also to that of Americans.

At least one-third of the background aerosol pollution (soot, smoke and dust particles, collectively called aerosols) in California today has floated across the Pacific from Asia, and this fraction is increasing. I collect and analyze air samples from four sites in the Sierra Nevada and Cascade mountains, and the filters in my samplers are tracking this trend. Of California’s annual average limit for particulate matter—12 micrograms per cubic meter of air—Asian pollution already accounts for 4–6 micrograms at these mountain sites.

China’s economic boom, combined with population growth in the western United States, is bound to push pollution levels beyond all California and US air quality standards.

Oceans, we now understand, do not insulate land masses from atmospheric conditions elsewhere. Any pollution that does not dissipate quickly will, with some variation, be transported by the prevailing westerly winds across the Pacific Ocean in less than a week. In the springtime, which is the dry season, a dust storm in the Gobi Desert of China and Mongolia can send a huge cloud over the US within three to five days, which then moves on to Greenland and Europe mixed with North American pollution.

One of the largest documented events of this kind happened in the spring of 2001 and was tracked by satellite. People throughout the West noted the hazy skies and asked about the location of the “fire.” In early April of this year, satellites tracked a large carbon cloud from Chinese coal-burning smokestacks crossing the Pacific.

Clearly, the air quality in the Northern Hemisphere is no longer a sovereign matter. It is affected by a combination of local, regional and long-range transported pollution.

We know that breathing small particles from carbon combustion can be bad for our health. We are also learning that these particles can influence climate. Scientists talk of aerosol climate effects that are positive and negative, direct and indirect feedback, but what it comes down to is this: We know that carbon dioxide (CO2) absorbs solar radiation, acting like a blanket and causing the greenhouse effect. Aerosols, however, are not a “single species” like CO2, but have varying compositions, sizes and concentrations. For example, in contrast with CO2, sulfates reflect sunlight and reduce warming.

Aerosol pollution’s indirect effects include those on cloud formation and precipitation. If there are a lot of very small particles from high-temperature combustion, such as coal burning, the water droplets that form don’t coagulate very well and thus don’t produce rain from clouds.

Also, some aerosols make clouds brighter. Brighter clouds reflect sunlight. Dark-particle pollutants that fall on top of snow can also make the mountain snow packs melt more quickly by absorbing sunlight. This reduces the water supply. And, despite the current worries over oil, in the end it is all about water.

Though we know it happens, we still have much to learn about the atmospheric dynamics that lead to the transport of pollutants across the seas and globally. We have even more to learn about their effects on climate change.

What we do know, though, is that the environmental problems associated with China’s rapid path to development affect us all. Only cooperation across boundaries will allow us to come to grips with both particulate pollution and CO2 emissions.

Fortunately, joint action on particle pollution can yield rapid improvements in air quality because these particles dissipate quickly, unlike CO2, which can remain in the atmosphere for decades or more. The time for that joint action is now.