The same high-pressure dome that keeps Phoenix over 110 degrees this week is also holding wildfire smoke at ground level, and the two hazards do not sit side by side. They stack. The Arizona Department of Environmental Quality has an Ozone High Pollution Advisory in effect for Maricopa County — which contains Phoenix — with a second advisory for neighboring Yavapai County, driven by smoke from the Pocket Fire north of Sedona and additional haze drifting in from California fires [1].

As this paper reported Monday, the compounding is the story, not the smoke alone. A dome of high pressure suppresses vertical mixing — the upward churn that normally carries pollutants away — so smoke and ozone settle exactly where the heat is already trapped. The Extreme Heat Warning for the Valley runs with highs near 110 to 117, and the AQI reading is not a nuisance number layered on top of it [2]. It is a second exposure for the same people: outdoor workers with no indoor refuge, and anyone with asthma, COPD, or a cardiac condition.

The service math is the point. Heat guidance says open windows at night to cool the house; smoke guidance says close them. On a stacked day, neither instruction is fully right. A cooling center with filtration addresses both. A cooling center without it addresses only one [1]. Check the AQI as a care number, not weather trivia — the dome is doing two things at once.

-- DARA OSEI, London