Themodel is among the first to project effects of future climate change onU.S. regional air quality, and they will be most dramatic in the West,this time of year. Come fall 2050, the model shows, a temperatureincrease of up to 4 degrees centigrade will contribute to a doubling ofstagnant, bad-air days—from one week to two—west of the Rockies to thecoastal mountains, said Ruby Leung, a fellow at the Department ofEnergy laboratory who led the study.
Bad air days are marked by"stagnation events," which occur when dry, windless air heats and fillswith dust, ozone and other [WG1] pollutants harmful to lungs and eyes.The model covers the period from 2045 to 2055, factoring inmeteorological elements relevant to air quality—temperature, solarradiation and cloud cover, and two that control the rate at whichpolluted air is diluted or flushed from a locale, ventilation andstagnation. A known period, 1995-2005, was used for comparison.
Thestagnation forecast in the West is limited to the fall, with noadditional drop in air quality forecast for the summer, a findingsimilar to most other regions of the country. Summer, however, is thepoor-air-quality season in Texas, and Texas will continue to warm by 2to 3 degrees centigrade and to stagnate, by nearly four additional daysat mid-century. Still, Leung reported, "it’s not a large changecompared to the average 15 days per season in the control simulation."
TheMidwest stands out in glaring contrast. The model predicts increasedcloud cover, which will in turn deflect the sun’s rays back towardspace, offsetting warming in the air near the surface for unchanged oreven cooler temperatures than today. There will be less stagnation, upto 8 fewer days a season, and more frequent rainfall, as many as sixextra days each season.
"Depending on the relative impacts ofthese parameters," Leung said, "ozone concentrations may remain similaror slightly decrease based on the simulated atmospheric changes alone."For more detailed projections of future air quality, Leung emphasizedthat "more studies need to be performed by including projections ofnatural and anthropogenic (human-produced) emissions and the complexchemical reactions that occur in the atmosphere."
PNNL staffscientist William Gustafson collaborated on the study, whose resultswere derived from the PNNL team’s regional climate model, driven byHarvard University global climate simulations using a NASA model.
PNNLis a DOE Office of Science laboratory that solves complex problems inenergy, national security, the environment and life sciences byadvancing the understanding of physics, chemistry, biology andcomputation. PNNL employs 4,000 staff, has a $700 million annualbudget, and has been managed by Ohio-based Battelle since the lab'sinception in 1965.
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