The Department of Environmental Conversation issued an air quality alert in effect until 10 p.m. Sunday.
All five New York boroughs, as well as Nassau, Suffolk, Westchester, and Rockland are under the advisory.
Bergen, Essex, Passaic, Union, and Hudson counties in New Jersey are also affected, with an alert lasting until 12 a.m. Tuesday.
Outdoor air is currently greater than an air quality index value of 100 out of 500 for ground ozone pollutant. The elevated levels are due to the very warm and humid conditions.
Gound ozone is commonly caused by pollutants from car and power plant emissions chemically reacting to sunlight.
The health department recommends that those who may be sensitive to elevated levels of pollutants take special precaution. Individuals should limit heavy exertion outdoors.