Bad Air Days in Westchester County, New York: 5 a Year

5 bad air days a year

More bad air days than three quarters of monitored counties. Ranked 212 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (8% particle days).

Which months to watch

Most bad days here fall in July and June and August and May. Averaged over 2016 to 2025.

What to buy, and what not to

Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.

The record for Westchester

In 2000 to 2009 this county averaged 18 bad days a year; in 2016 to 2025, 5. The air has improved. The worst recent year was 2018, with 12 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-07	198	PM2.5
2018-07-02	169	Ozone
2023-06-08	153	PM2.5
2023-06-30	151	Ozone
2023-06-06	144	PM2.5

An ordinary day in Westchester

Across 3,647 monitored days from 2016 to 2025, the air in Westchester County rated Good on 81% of them, more often than the 72% typical of monitored counties, and Moderate on 17%. The median day sat at AQI 38; one day in ten went above 57.

The pollutant setting the AQI on an ordinary day here:

ozone68%2,484 days
fine particles (PM2.5)32%1,163 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	301	58	6	0	38	136
2024	365	302	57	6	0	36	143
2023	365	287	71	7	3	39	198
2022	365	300	65	0	0	38	100
2021	365	307	52	6	0	38	143
2020	363	305	57	1	0	38	105
2019	365	309	55	1	0	38	105
2018	365	295	58	12	1	38	169
2017	363	292	66	5	0	38	112
2016	366	269	91	6	0	40	140
2015	365	231	125	9	0	43	140
2014	365	237	124	4	1	44	154
2013	365	249	110	6	0	42	136
2012	366	244	111	11	1	43	151
2011	362	207	150	5	2	46	182
2010	365	238	113	14	0	43	150

*2025 may be a partial year in EPA's file.

Nearby counties on file

How this is counted

A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.