October 24, 2014
Moderate AQI Across Midwest
The EPA AQI loop below left shows a swath of Moderate AQI
from the Great Lakes through the Great Plains and into the
Mississippi Valley. This area corresponds in part to the
areas of high NO2 shown in the Tropospheric
NO2 image below right. There are also patches
of Moderate AQI in the Pacific Southwest and Southeast.
The NPS webcam image below left shows the view from Big
Bend National Park in southwest Texas, on the edge of the
area of Moderate AQI shown in the image above. Images taken
in clear and hazy conditions are shown below right for
comparison. The image shows somewhat hazy conditions, in
keeping with the AQI levels around that area.
October 23, 2014
Moderate AQI in California and Great Lakes
Moderate AQI levels were experienced in several regions throughout the day. California and the Pacific Northwest registered some moderate levels. The great Lakes, the Mississippi Valley and some of the Plain States also reached moderate levels (top left). NRL/Monterrey aerosol modeling reported smoke over Mississippi, Alabama and Louisiana (top left). A sulfate belt was also reported extending from Oklahoma, through the Great lakes up to northern Canada.
Special Feature: Measuring Earth's Albedo
Sunlight is the primary driver of Earth's climate and weather. Averaged over the entire planet, roughly 340 watts per square meter of energy from the Sun reach Earth. About one-third of that energy is reflected back into space, and the remaining 240 watts per square meter is absorbed by land, ocean, and atmosphere. Exactly how much sunlight is absorbed depends on the reflectivity of the atmosphere and the surface.
As scientists work to understand why global temperatures are rising and how carbon dioxide and other greenhouse gases are changing the climate system, they have been auditing Earth's energy budget. Is more energy being absorbed by Earth than is being lost to space? If so, what happens to the excess energy?
For seventeen years, scientists have been examining this balance sheet with a series of space-based sensors known as Clouds and the Earth's Radiant Energy System, or CERES. The instruments use scanning radiometers to measure both the shortwave solar energy reflected by the planet (albedo) and the longwave thermal energy emitted by it. The first CERES went into space in 1997 on the Tropical Rainfall Measuring Mission, and three more have gone up on Terra, Aqua, and Suomi-NPP. The last remaining CERES instrument will fly on the JPSS-1 satellite, and a follow-on, the Radiation Budget Instrument (RBI), will fly on JPSS-2.
If Earth was completely covered in ice, its albedo would be about 0.84, meaning it would reflect most (84 percent) of the sunlight that hit it. On the other hand, if Earth was covered by a dark green forest canopy, the albedo would be about 0.14 (most of the sunlight would get absorbed). Changes in ice cover, cloudiness, airborne pollution, or land cover (from forest to farmland, for instance) all have subtle effects on global albedo. Using satellite measurements accumulated since the late 1970s, scientists estimate Earth's average albedo is about about 0.30.
The maps below show how the reflectivity of Earth--the amount of sunlight reflected back into space--changed between March 1, 2000, and December 31, 2011. This global picture of reflectivity (also called albedo) appears to be a muddle, with different areas reflecting more or less sunlight over the 12-year record. Shades of blue mark areas that reflected more sunlight over time (increasing albedo), and orange areas denote less reflection (lower albedo). At the North Pole, reflectivity decreased markedly, a result of the declining sea ice on the Arctic Ocean and increasing dust and soot on top of the ice. Around the South Pole, reflectivity is down around West Antarctica and up slightly in parts of East Antarctica, but there is no net gain or loss. At the same time, Antarctic sea ice there has been increasing slightly each year. Full article: Earth Observatory
October 22, 2014
Moderate PM2.5 in the Southern Mississippi Valley States; Coarse Particulate over Rocky Mountain and Plain States
Moderate PM2.5 concentrations were observed in Southern Mississippi Valley States, shown in the EPA Airnow animation, as sunny skies, warm temperatures and light winds favored particle pollution production. Satellite retrievals over the nation show that AOD levels did not exceed values greater than 0.2, with the greatest values observed over the northern Rocky Mountain and western Plains States. According to the Naval Research Laboratory aerosol model particles over this region are most likely to be dust. Aeronet optical column size distribution retrieved over Bozeman, Idaho show the presence of coarse particulate (radius in the range of 1-10 microns) aloft.
October 21, 2014
Moderate AQI in Texas and Mississippi Valley Region. Increased NO2 in Ohio River Valley.
The EPA AQI image, below left, shows areas of Moderate AQI in parts of California, Texas, and the Mississippi Valley region. The VIIRS AOD retrieval, bottom right, shows very minimal increases in AOD throughout the country. There are some increases corresponding to the Moderate AQI in Texas.
The surface PM 2.5 model, courtesy NAAPS below left, shows continuing dust blowing in the Pacific Northwest region. This model also shows an increase in the surface sulfates in Texas and in the Ohio River Valley. The OMI NRT NO2 retrieval picks up an increases in the NO2 in the troposphere that appears to be in a similar region as the sulfates from the NAAPS model.
October 19, 2014
Weekend Edition: Lovely weather over the US
Outside of a curious code red in the eastern desert of California, most of the US is code green or isolated areas of moderate AQI. The AQI reading in California maximized Sunday morning at 11:00 AM but there are no stations shown on AIRNOW which correspond to such elevated AQI readings. Perhaps someone has an explanation or it may be an anomalous report.
In Maryland, we could not have had a more beautiful day. The Baltimore Webcam shows you can see forever and on the very left of the image, Baltimore's Ravens clobbered the Atlanta Falcons. Go birds. And good luck to the Giants on Tuesday.
October 17, 2014
Spots of Moderate AQI as Gonzalo hits Bermuda
October 16, 2014
Good air quality in the US; Dust in Utah and Idaho
Today most of the U.S. experienced good air quality except in California where moderate levels were recorded throughout the day (top left). Moderate levels were also reached in Louisiana and in the Great lakes region. Although some fires took place in different states, HMS indicated that no significant smoke was produced out of those fires (top right). However, a relatively small area of blowing dust was visible moving eastward over northern Utah, over Great Salt Lake, into southern Idaho, and currently reaching the Utah/Wyoming border. This dust originates from sand dunes located directly west of Great Salt Lake. NRL modeling also predicted dust in the same region as well as sulfate in the Eastern states (bottom).
SPECIAL FEATURE: Smoke Above the Clouds
If you look at satellite imagery of Earth on a browser like Worldview or NOAAView, a few important features of the atmosphere become obvious. First, clouds dominate the view. They cover about 60 percent of the planet at all times, and the percentage is even higher over oceans, where banks of low-lying stratocumulus clouds often form. Second, plumes of smoke, dust, and industrial haze--which are made up of airborne particles called aerosols--often darken portions of the atmosphere.
What happens when these two atmospheric heavyweights--clouds and aerosols--meet? Scientists at NASA are working to understand this. "One of the key uncertainties remaining in climate science relates to how clouds and aerosols interact," explained Hiren Jethva, a scientist at Goddard Space Flight Center. "And one of the reasons for that relates to what happens when aerosols end up above the cloud layer."
Aerosols can rise or get blown above clouds. They often do just that between July and September in Central Africa, where agricultural fires produce plumes of smoke that blow offshore and drift over low-lying clouds in the southeastern Atlantic. Similar aerosol-over-cloud situations occur in other parts of the world. Saharan dust blows over clouds in the Atlantic, and smoke from southeast Asia hovers over clouds in the Pacific. "Aerosols elevated above clouds can travel faster and longer than those near the surface, implying far-reaching impacts," explained Hongbin Yu, an atmospheric scientist at Goddard.
The images above come from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on the CALIPSO satellite and the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite. They show a smoke plume elevated above a cloud layer in the southeastern Atlantic on September 10, 2014. The smoke came from agricultural fires in central Africa, which were widespread in that region in September. The background (top) image was captured by MODIS and provides a true-color view of the smoke and clouds from above. The yellow line indicates the path of the CALIPSO satellite and its laser, which sent pulses of light (lidar) down through the atmosphere and recorded the reflections in a vertical profile (lower image). The MODIS image has been rotated (north is to the right) so that the line that depicts the CALIPSO flight track is aligned horizontally.
Whether smoke or dust hovers above clouds or in a cloud-free environment can lead to very different impacts on the atmosphere and climate. "To put it simply, smoke or dust in cloud-free conditions generally causes a cooling of the Earth-atmosphere system," said Yu, "whereas the same types of particles may have a warming effect if they are located above clouds."
Why the difference? Smoke and dust plumes contain large number of "absorbing aerosols"--particles that both scatter and absorb the energy in sunlight. In cloud-free conditions, the scattering effect dominates, and the particles reflect more solar radiation back to space than underlying dark surfaces such as the ocean or a forest. This produces a cooling effect.