WATERTOWN — An Air Quality Advisory is in effect for parts of the north country between 11 a.m. and 11 p.m. Friday.
The state Department of Environmental Conservation announced ground-level ozone as the pollutant of concern for three of the state’s eight Air Quality Health Advisory regions: Western New York, Eastern Lake Ontario and Central New York.
With an “Unhealthy for Sensitive Groups” advisory Friday, the Eastern Lake Ontario region is comprised of Jefferson, Monroe, Oswego, Wayne and northern Cayuga counties.
A moderate Air Quality Index score, not constituting an advisory, is logged for the Adirondack region: St. Lawrence, Lewis, Franklin, Essex, Clinton, Hamilton, Warren and northern Herkimer counties.
An advisory for Eastern Lake Ontario and Western New York was also issued Wednesday.
State air pollution meteorologists work every morning to develop regional AQI forecasts for the next day. AQI values are averaged and based on dozens of air quality monitoring devices and stations, wind direction and speed data, satellite images from NASA and the National Oceanic and Atmospheric Administration and long-term, seasonal pollution data.
The AQI is scaled across six levels with accompanying scores between zero and 500. Category Good reflects a score between zero and 50; Moderate is 51 to 100; Unhealthy for Sensitive Groups is 101 to 150; Unhealthy is 151 to 200; Very Unhealthy is 201 to 300; and Hazardous is 301 to 500.
Advisories are typically issued when scores are expected to exceed 100. Each level carries elevated health concerns, particularly for older adults, people with asthma and people with cardiovascular conditions.
Preliminary data collected as of 8:56 a.m. Friday notes observed AQI scores falling in the moderate category for Eastern Lake Ontario.
With ground-level ozone levels generally lower in winter, according to the DEC, daily forecasts for ozone pollution are usually only developed in warmer months, between April and September.
Ozone exists in Earth’s upper atmosphere and at ground level as a gas composed of three oxygen atoms, O3. Stratospheric ozone molecules are constantly being broken and reformed, with natural annual cycles tracked by agencies around the world.
The ozone layer in Earth’s stratosphere absorbs harmful ultraviolet light from the sun, and has been observed over several decades to have diminished to thin patches as a result of ozone-depleting substances, mostly containing chlorine and bromine.
But ground-level ozone — from vehicle and industrial emissions chemically reacting to sunlight — is an air pollutant that in high enough levels irritates the lungs, eyes and nose, and primarily contributes to smog, though the molecule can be harnessed for lab and practical uses.
The DEC also monitors for fine particles, carbon monoxide, methane and other hydrocarbons, sulfur dioxide and nitrogen oxides.