U.S. deep freeze continues; dangerous air pollution episode in Utah

The January 2013 North American cold wave continued to bring bitter cold to much of Eastern Canada and the Midwest and Northeast U.S. this morning. In the U.S., below-zero temperatures were recorded Thursday morning in twelve states east of the Rockies. The most intense cold was centered near the Minnesota/Ontario border, where Embarrass, Minnesota hit -42°F (-41°C) and Crane Lake, Minnesota bottomed out at -36°F (-38°C). The coldest spot in Canada was in Souix Lookout, Ontario, about 100 miles north of International Falls, where the mercury fell to -40°F (-40°C.) The fun continued on the summit of Mt. Washington, New Hampshire this morning, where a temperature of -26°F (-32°C) combined with a wind of 71 mph to create a remarkable wind chill of -73°F (-58°C). A digression: back in 1986, when I taught weather forecasting at SUNY Brockport in New York, I worked with a meteorologist who used to work on top of Mt. Washington as a weather observer. He said it was standard practice back in the days he worked there to engage in a ritualistic prank whenever a new weather observer joined the staff. On the first day the new observer was there during one of Mt. Washington's classic hurricane-force wind events, he would be sent out with a safety harness and a can of paint to paint the observation platform. The unwitting observer would inch out into the hurricane winds, struggle to pry off the lid of the can of paint, and quickly discover the impossibility of painting during a hurricane--the powerful winds blowing over the top of the paint can would create a powerful Bernoulli Effect, levitating the paint out of the can and hurling all of the paint far downwind. The sheepish newbie weather observer would report back inside and ask, "you really didn't want me to paint the observing platform, did you?" to the sound of uproarious guffaws.


Figure 1. A cold day in New England: cold air flowing off of the New England coast creates thick stratocumulus clouds over the Atlantic Ocean in this true-color MODIS satellite image taken at 12:35 pm EST January 23, 2013. Image credit: NASA.

Dangerous air pollution in Utah
The most dangerous weather in the U.S. this week is occurring in the valleys of northern Utah, where clear skies, light winds, and a strong temperature inversion have combined to create a dangerous 6-day long air pollution episode. (A temperature inversion occurs when air temperature increases with altitude, acting as a stable lid preventing atmospheric mixing; inversions are common in mountain valleys when high pressure dominates.) It's been unusually cold during most of January in Northeast Utah, with Salt Lake City on track to have its 3rd coldest January on record. The cold weather has caused people to use their wood burning stoves more than usual, resulting in high emissions of smoke. More than 100 Utah doctors delivered a petition to state lawmakers on Wednesday, demanding that authorities immediately lower highway speed limits, curb industrial activity and make mass transit free for the rest of winter. "We're in a public-health emergency for much of the winter," said Brian Moench, an anesthesiologist and president of Utah Physicians for a Healthy Environment. He estimated that poor air quality contributes to 1,000 to 2,000 premature deaths each year along Utah's Wasatch Front.


Figure 2. View of a smoggy Salt Lake City taken at 2 pm MST January 23, 2013. Webcam image courtesy of University of Utah/TimeScience.

Winds have remained below 6 mph for six straight days in Northern Utah, allowing fine Particulate Matter less than 2.5 microns in diameter (also called PM 2.5) to build up to unhealthful levels. PM 2.5, also known as particle pollution, is a complex mixture of extremely small dust and soot particles that lodge in the lungs and cause large increases in hospital admissions and excess mortality during severe air pollution episodes like this one. The federal standard for PM 2.5 is 35 micrograms per cubic meter, averaged over 24 hours. In Salt Lake City, fine particle air pollution has been above the federal standard for six consecutive days, with a peak value of 91 micrograms per cubic meter on January 19. In nearby Provo, Utah, the pollution has been much worse, with 24-hour average PM 2.5 levels more than triple the federal standard on Thursday morning, at 131 micrograms per cubic meter. If the PM 2.5 levels go above 150 micrograms per cubic meter, this will be in the "Very Unhealthy" category as defined by EPA. At this pollution level, the entire population is likely to be affected, and health warnings of emergency conditions are issued. Compounding the air pollution woes in Provo are high levels of nitrogen dioxide gas, which peaked at 98 ppb on Tuesday, just below the 100 ppb federal standard. Light winds and a strong temperature inversion will continue today, and freezing rain fell over much of the Salt Lake City area this morning, turning the roads into skating rinks, resulting in dozens of traffic accidents. Fortunately, the forecast for Provo calls for snow and rain this weekend due to a low pressure system, and the rain and winds associated with this low should be able to reduce air pollution levels significantly.


Figure 3. Observed air quality in North Provo, Utah, January 19 - 24, 2013. 24-hour average fine Particulate Matter less than 2.5 microns in diameter (also called PM 2.5) levels (black circles, top image) were in excess of the 35 micrograms per cubic meter U.S. standard (orange line) during the entire period, and peaked at 131 micrograms per cubic meter--more than 3 times the Federal standard--Thursday morning. Levels of toxic nitrogen dioxide (yellow dots) peaked at 98 ppb, just below the U.S. standard of 100 ppb, on January 22. Note that during the entire 5-day period pictured here, the wind speed at the surface never rose above 6 mph (lower image, black dots.) Image credit: Utah DEQ.

Jeff Masters