It is a machine that monitors fine particulate matter, one of the most dangerous components of air pollution, and instantly posts the results to Twitter and a dedicated iPhone application, where it is frequently picked up by Chinese bloggers.
One day this month, the reading was so high compared with the standards set by the U.S. Environmental Protection Agency that it was listed as "beyond index." In other words, it had soared right off the chart.
"You couldn't get such a high level in the United States unless you were downwind from a forest fire," said Dane Westerdahl, an air quality expert from Cornell University.
But China's own assessment that day, Oct. 9, was that Beijing'sair was merely "slightly polluted."
Not even the most fervent propagandist would call the city's air clean, but the Chinese government made great efforts to improve air quality for the 2008 Olympic Summer Games. Beijing authorities moved huge steelworks out of the capital, switched city dwellers from coal to natural gas heating, raised emissions standards for trucks, and created new subway and bus lines. The cost of the cleanup was estimated at $10 billion, not including the investment in mass transit.
Three years later, the difference between the Americans and the Chinese is at least in part about what they're measuring. And it highlights the rapid growth in the number of cars in Beijing.
Chinese monitoring stations around the capital track large particulates of up to 10 micrometers. The number of those particles has dropped as a result of reforestation programs that lessen the dust storms that blew in from deserts. The Chinese have also been successful in reducing sulfur dioxide emissions by limiting coal heating and imposing stricter emissions standards.
The U.S. monitor tracks tinier particles — less than 2.5 micrometers — that physicians say are capable of penetrating human lungs and other organs. Car and truck exhaust is a major source of fine particulate pollution, a particular problem in Beijing, where the number of registered cars has skyrocketed from to 5 million from 3.5 million in 2008.