Credit: Curt Carnemark / World Bank.[/caption
By now, you have probably seen terrifying images of the catastrophic air pollution that has plagued Beijing, China, in recent weeks. Report after report has shown apocalyptic images of the city blanketed with clouds of pollution, snarled traffic due to low visibility and distressed citizens protecting themselves with face masks (see this lovely gallery from The Atlantic
). Doctors in Beijing reported increases in hospital emissions for respiratory complaints, especially among children. Two Chinese software companies that develop smartphone apps for monitoring pollution exposure reported huge spikes in their downloads
for 5RMB (about 80 cents). I wiped my brow when I learned that Chen "is well known for his ... publicity stunts" and that he's actually selling air "to stimulate awareness of environmental protection among government officials and citizens."
Smog in Beijing. Credit: bfishadow, CC BY 2.0.[/caption
At the time of this writing, a change in the weather seems to have blown away the dangerous smog for now (yay). But when the temperature inversion system that trapped all that pollution-laden air over the city returns, so will the dangerously high levels of fine particulate matter pollution (PM2.5, referring to solid particles and droplets of fluid of 2.5 microns or less).
Could it happen in the U.S.? After all, temperature inversions occur here, too. According to the U.S. National Oceanic and Atmospheric Administration
(NOAA), an inversion is "a departure from the usual increase or decrease in an atmospheric property with altitude," usually referring to "an increase in temperature with height, or to the layer within which such an increase occurs." An inversion traps pollution close to the ground. The West Coast of the U.S. is particularly vulnerable to inversions, according to the mechanical engineering school at the University of Michigan. A tutorial
from the school says that "Los Angeles is a prime example of a location that is prone to inversions" in which "pollution does not dissipate, causing large amounts of smog and air pollution."
The U.S. Embassy in Beijing monitors air quality continuously and tracks it on its website
, so you can see the current Air Quality Index (AQI) level in the city at any time. You can also follow Beijing air quality on the BeijingAir Twitter feed
from AIRNow, an index and monitoring service established by the U.S. Environmental Protection Agency (EPA) and other government agencies.
A brochure from the EPA
explains that the AQI is a number used to measure air pollutants, especially PM2.5, and to communicate "how clean or polluted your air is, and what associated health effects might be a concern for you." An AQI of 0 to 50 is "Good" (color-coded green); 51 to 100 is "Moderate" (yellow); 101 to 150 is "Unhealthy for Sensitive Groups" (orange); 151 to 200 is "Unhealthy" (red); 201 to 300 is "Very Unhealthy" (purple); and 301 to 500 is "Hazardous" (maroon).
AQI chart. Credit: EPA.[/caption
When this article was about to be published (9 a.m. on Feb. 4, 2013, Beijing time), the AQI in Beijing was 57 -- "Moderate" on the AQI. During the previous 24 hours, AQI ranged from a low of 39 ("Good") to a high of 289 ("Very Unhealthy"). You can see that the air pollution level is a moving target.
On Saturday, Jan. 12, Beijing's AQI actually reached an astonishing 750 -- off the EPA's scale.
"How can a measurement be a 750 on a 500 scale?" Flora Lichtman
of National Public Radio (NPR) asked David Pettit
, director of the Southern California Air Program at the Natural Resources Defense Council (NRDC). Pettit told Lichtman,
I think it means that the engineers who built the scale thought it was ridiculous to have numbers any higher than they did because a circumstance like that would never occur. It's like having ... your car's speedometer go up to 500 miles an hour. Why would you need that?
EPA says that
"An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health." So if Beijing is registering an AQI of way over 500, you know things are bad. On Jan. 17, when Pettit was speaking to NPR, he said, "in Beijing ... the direct reading was about 30 times the United States limit on a 24-hour basis. So it's just unimaginably bad by U.S. standards."
Pettit explained that when Beijing experiences a temperature inversion, "the colder air sort of sits on a lid in the Beijing area and prevents the warmer air underneath from moving around." Beijing has many cars, and people burn coal for heat in the winter. "You put that all together, you know, with a zero wind condition and that's a recipe for environmental disaster." Such conditions are very dangerous for young children and for people with compromised lung functions such as asthmatics.
Chang'an Avenue in Beijing. Credit: Australian cowboy, Wikimedia Commons.[/caption
Where does all that pollution come from? Louise Watt of Huffington Post
reports that "While burning of coal for power plants is a major source of air pollution across China, vehicle emissions are the single biggest source of PM2.5" in Beijing. She writes that the Chinese government has promoted car-buying as a way to grow the country's economy and has prompted banks to offer attractive loans. More than 13 million cars were sold in China in 2012. The number of cars in Beijing has grown from 3.13 million in early 2008 to 5.18 million today.
The kind of temperature inversion experienced in Beijing can occur in the United States, for example, in Los Angeles, Pettit told NPR. Problems such as Beijing is experiencing are unlikely in the U.S., he said, thanks to environmental protections we enjoy here: "The EPA has really cracked down in, you know, the last couple of decades on emissions from coal plants, and the automobiles are much better controlled than they've ever been, so I really don't see this happening here in the U.S."
Air pollution in the U.S. is decreasing, thanks to energy-saving technologies and reductions in coal-fired power generation. Considering carbon emissions as a good proxy for overall air pollution, a report from Bloomberg New Energy Finance
says that carbon emissions from energy and transport "peaked in 2007 at 6.02Gt and have dropped by an estimated 13 percent since" and "are now at their lowest level since 1994." China, on the other hand, is the world's largest emitter of carbon and the largest energy consumer. According to figures from the U.S. Energy Information Agency
(EIA), China consumes almost as much coal as the rest of the world combined.
If you want to monitor AQI levels in the U.S. you can check the AIRNow website
. The U.S. Air Quality Summary page
gives the state-by-state current AQI, forecast and archives. You can download an Android mobile app
from the AIRNow site as well. An iPhone app
is available from iTunes.
Credit: Energy Information Administration[/caption