New England flooding, air pollution, and the season's first typhoon

Major flooding has hit southern New Hampshire, southwest Maine, and northeast Massachussetts today, where more than 10 inches of rain has fallen in the past four days. The culprit is a "cut off low", a large low pressure system over the Great Lakes that got separated from the jet stream on Thursday, and has stayed almost stationary since since then, with no upper level winds to push it along. The counter-clockwise flow of air around the low has drawn copious amounts of moist oceanic air over New England. The rains from this moisture have brought the Warner river at Davisville and the Smith River at Bristol to flood stage this morning. With another 1-2 inches of rain expected across the region today, these rivers should crest several feet above flood stage, with moderate to major flooding. The cut-off low is expected to drift slowly northeastward today and get re-absorbed by the jet stream on Tuesday, which will finally bring an end to the worst of the rains. Howver, the weather pattern over the next week is expected to remain wet over the eastern half of the U.S., and more rain is expected in the Northeast later this week as the jet stream continues to remain in a typical Springtime active pattern.


Figure 1. Rainfall amounts for New England estimated by radar, ending at 8:30am EDT Monday May 15.

Air pollution season is here
May marks the beginning of air pollution season in the U.S., when summertime brings the hot temperatures, high amounts of UV radiation, and stagnant air that can trigger air pollution "Action Days". This week marks the annual observance of Air Pollution Awareness week, and at EPA's request, I will be writing several blogs highlighting air pollution. In particular, I'll discuss why one of NOAA's P-3 hurricane hunter airplanes will be in Texas for air pollution research this hurricane season, instead of flying hurricanes.

Quick intro on air pollution
Today, I'll present a quick summary of what pollutants we're concerned about. The Environmental Protection Agency (EPA) calculates the Air Quality Index (AQI) for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Ozone and particle pollution are the two most serious pollutants in the U.S. Particle pollution alone has been estimated to cause over 20,000 premature deaths the U.S. each year, and 800,000 worldwide (although the exact mortality numbers and definition of "premature deaths" is controversial).

Ozone is a colorless gas composed of three atoms of oxygen. Ozone forms both in the Earth's upper atmosphere and at the surface. Where ozone forms determines whether it is helpful or harmful to your health.

Good ozone naturally forms in the stratosphere, a layer of air about 10 - 30 miles (16 - 48 km) above Earth's
surface. This protective layer shields us from the sun's harmful ultraviolet rays. Without this layer, we would all be blinded and sunburned. Unfortunately, human-created chemicals are destroying this beneficial layer of ozone. Over the South Pole in springtime, the ozone loss is so severe that an "Ozone Hole" forms, letting significant amounts of harmful ultraviolet light reach the surface.

Ozone from the stratosphere sometimes gets transported to the surface, particularly in high mountainous regions. Hikers on Mt. Everest who don't use bottled oxygen can be at risk of death from breathing poisonous levels of ozone near the mountain's summit in some weather conditions.

Bad ozone forms near Earth's surface when the ultraviolet light in sunlight triggers a chemical reaction with "precursor pollutants" emitted by cars, power plants, and industrial sources. These precursor pollutants consist of nitrogen oxides (NOx) and volatile organic hydrocarbons (VOC). Ozone near ground level is a harmful pollutant. Ozone pollution isn't limited to big cities like Los Angeles, Houston and New York. It's also found in smaller cities like Raleigh, NC and Cincinnati, OH. It can be a problem in rural areas, including some national parks. Ozone and the pollutants that react to form it (NOx and VOCs) can also be carried on the wind to affect air quality in urban and rural areas hundreds of miles away.

Particle pollution is a mixture of microscopic solids and liquid droplets suspended in air. This pollution, also known as particulate matter, is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, soil or dust particles, and allergens (such as fragments of pollen or mold spores). Unlike summertime ozone, particle pollution can occur year-round. It is worst in summer, though, when winds are lighter and the air becomes more stagnant.

Particles come in a wide range of sizes. Fine particles are less than 2.5 micrometers in diameter. How small is that? About 1/30th the diameter of the average human hair--so small, you'd need an electron microscope to see them.

Some fine particles can be emitted directly (think of smoke from a woodstove). But most are formed secondarily from complex atmospheric reactions of gases such as NOx and sulfur dioxide (SO2), that are emitted from power plants, industries, cars, buses and trucks. These fine particles are the worst for your health, since their small size allows then to penetrate deep into your lungs.

Inhalable coarse particles are larger than 2.5 and up to 10 micrometers in diameter. Sources of coarse particles include crushing or grinding operations and dust stirred up by vehicles traveling on roads. These particles are not as injurious to your health, as their large size allows them to be filtered out more readily by your nose before they reach your lungs.

Typhoon Chanchu
The season's first typhoon, a Category 4 storm with 140 mph winds named Chanchu, has turned north, and is now threatening to strike Hong Hong on Wednesday. Chanchu briefly made it to supertyphoon status on Sunday, when it had 150 mph sustained winds and a 910 mb central pressure. This was good enough for a Category 4 rating on the U.S. Saffir-Simpson scale, but not Category 5--which starts at 156 mph. A supertyphoon is defined as any tropical cyclone in the Western Pacific that attains maximum sustained winds of 150 mph. It is not unusual to get a supertyphoon in May, and this last happened in 2004, when Supertyphoon Nida reached Category 5 status with sustained winds of 160 mph. I'll have more on Typhoon Chanchu tomorrow.


Figure 2. Typhoon Chanchu at peak intensity Sunday, with 150 mph sustained winds and a 910 mb pressure.

Jeff Masters