After a soaking weekend nor'easter along the Eastern Seaboard, air-quality desks watched local Air Quality Index (AQI) readings rather than treating wildfire smoke as the Northeast's lead Sunday story. Rain and wind can scrub some particles from the air in one county while lofting dust or smoke into another, so the same storm system rarely leaves a uniform map.

The U.S. AQI is EPA's color-coded tool for outdoor air and health. Values from 0 to 50 (green) mean air quality is satisfactory. Fifty-one to 100 (yellow) is acceptable, with some risk for people who are unusually sensitive to pollution. Above 100, air turns unhealthy first for sensitive groups (orange, 101–150), then for more of the public as the index climbs through red (151–200), purple (201–300), and maroon (301 and higher). EPA builds the index from five Clean Air Act pollutants: ground-level ozone, particle pollution (including PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide.

Particle pollution is the storm-season piece that matters most for these weekend checks. Particulate matter is a mix of solid particles and liquid droplets — dust, dirt, soot, and smoke. Some particles come straight from roads, construction sites, fields, fires, or smokestacks. Others form in the air when sulfur dioxide and nitrogen oxides from power plants, industry, and vehicles react. Fine particles (PM2.5) can reach deep into the lungs and even the bloodstream; they are also a main cause of haze in many U.S. parks and cities.

NOAA and EPA partner on daily air-quality forecast guidance. National Weather Service safety pages note that poor air still drives large health costs nationwide and that ozone and particulate forecasts exist so people can limit exposure. Sensitive groups — people with asthma, heart or lung disease, older adults, and children — are usually the first to need care when the index rises.

For a practical check, AirNow.gov shows the current national AQI map and points to the Fire and Smoke map when wildfire plumes are an issue in other regions. State environmental pages and local NWS offices add county-level detail. A green or yellow reading after heavy rain is common; orange or worse means cut outdoor exertion and follow the activity guidance tied to that color.