Take a Deep Breath, Beijing! U.S. Embassy Deploys Ozone Monitor

BEIJING—For many of the expats here in one of the world’s most polluted cities, a morning ritual is checking the latest local air-quality readings. This week, a trusted source—the U.S. Embassy’s air-pollution monitor—got a whole lot more interesting.

The embassy has been using Twitter to publish average hourly readings of particulate matter that’s less than 2.5 micrometers in diameter (PM2.5): fine particles from combustion and industrial emissions that penetrate deeply into the lungs and are linked to heart disease and other health problems. This week, without fanfare, it also started tweeting hourly data on ground-level ozone, the prime component of smog. Most in China can’t see these data, however. Twitter is blocked in China; thus, accessing the site requires a proxy server or virtual private network.

In a statement, the embassy noted that the additional ozone information will help the embassy community “make better daily decisions regarding the safety of outdoor activities.” The embassy’s monitor, located at its compound in northeast Beijing’s Chaoyang District, offers a different perspective on citywide readings posted by the Ministry of Environmental Protection, which focuses on PM10 and sulfur dioxide.

Today, on a late Friday afternoon with many Beijingers having already returned to their hometowns for the start of the spring festival, air quality happens to be pretty good. At least it’s nothing like 19 January, when the air in Beijing reeked. In that brownish-yellow miasma, PM2.5 readings were off the chart and the corresponding air-quality index warned of “emergency conditions” that could affect the whole population. Nonetheless, longtime residents insist that the air here is getting better.