Bad Air Days in Nassau County, New York: under 1 a Year

under 1 bad air day a year

Rare: among the cleanest-air counties EPA monitors. Ranked 815 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (100% particle days).

When the bad days come in Nassau

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

Is a purifier worth it here?

Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
On the odd bad day, check AirNow and keep windows shut.

The worst days on file

In 2000 to 2009 this county averaged 2 bad days a year; in 2016 to 2025, under 1. Not much has changed. The worst recent year was 2023, with 4 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-07	197	PM2.5
2023-06-08	157	PM2.5
2023-06-06	155	PM2.5
2023-06-30	125	PM2.5
2021-07-20	118	PM2.5

Most days, not the worst ones

Across 3,604 monitored days from 2016 to 2025, the air in Nassau County rated Good on 82% of them, more often than the 72% typical of monitored counties, and Moderate on 18%. The median day sat at AQI 30; one day in ten went above 55.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)100%3,604 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	364	287	77	0	0	29	92
2024	366	308	58	0	0	31	71
2023	365	275	86	4	3	31	197
2022	361	303	58	0	0	29	68
2021	360	291	68	1	0	32	118
2020	361	317	44	0	0	27	75
2019	360	308	52	0	0	29	72
2018	365	305	60	0	0	28	93
2017	347	277	70	0	0	32	68
2016	355	278	77	0	0	30	72
2015	362	256	106	0	0	34	80
2014	359	260	99	0	0	36	79
2013	356	220	136	0	0	43	96
2012	334	180	154	0	0	46	87
2011	343	159	182	2	0	52	108
2010	365	209	156	0	0	44	96

*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.