Arizona, Colorado and Texas issued ozone alerts on Tuesday as a stretch of dangerous heat and sunny, stagnant conditions pushed air quality toward unhealthy levels in several regions, with officials asking drivers to cut back on gas- and diesel-powered trips through Tuesday afternoon.
In Arizona, the Department of Environmental Quality put Maricopa County, including the Phoenix metro area, under an Ozone High Pollution Advisory through Tuesday. The National Weather Service in Phoenix said dangerously hot conditions of 105°F to 110°F were expected across the greater Phoenix region until 8 PM MST Tuesday, covering Phoenix, Mesa, Chandler, Scottsdale and Glendale. The combination of that heat and existing ozone levels could produce 8-hour ozone concentrations that pose a health risk.
Farther north, the Colorado Department of Public Health and Environment issued an Ozone Action Day Alert for the Front Range Urban Corridor until Tuesday afternoon, covering Douglas, Jefferson, Denver, western Arapahoe, western Adams, Broomfield, Boulder, Larimer and Weld counties. The agency said ozone concentrations could reach Unhealthy for Sensitive Groups through Tuesday. In Texas, the Commission on Environmental Quality posted an Ozone Action Day for the El Paso area throughout Tuesday until Tuesday night.
The pattern fits the way ground-level ozone is made: nitrogen oxides and volatile organic compounds react in sunlight, and warm, sunny, stagnant-weather days often trigger episodes. Transportation emissions are a major source of nitrogen oxides and also add volatile organic compounds, which is why officials are urging people in affected areas to limit driving gas- and diesel-powered vehicles. For residents across the Southwest and the Front Range, the immediate issue is not just the heat itself but the air it is helping turn unhealthy through Tuesday.
