Bad Air Days in Sussex County, Delaware: 1 a Year

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 589 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (40% particle days).

Which months to watch

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

What actually helps 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 record for Sussex

In 2000 to 2009 this county averaged 32 bad days a year; in 2016 to 2025, 1. The air has improved. The worst recent year was 2023, with 6 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-07	203	PM2.5
2023-06-08	187	PM2.5
2023-06-29	162	PM2.5
2018-07-10	140	Ozone
2016-05-25	129	Ozone

An ordinary day in Sussex

Across 3,652 monitored days from 2016 to 2025, the air in Sussex County rated Good on 73% of them, close to the 72% typical of monitored counties, and Moderate on 27%. The median day sat at AQI 42; one day in ten went above 59.

The pollutant setting the AQI on an ordinary day here:

ozone60%2,204 days
fine particles (PM2.5)40%1,448 days

Sussex County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	300	64	1	0	39	105
2024	365	298	67	0	0	40	90
2023	365	215	144	6	3	47	203
2022	365	274	91	0	0	43	87
2021	365	277	88	0	0	40	100
2020	366	286	80	0	0	42	87
2019	365	251	114	0	0	44	93
2018	365	256	105	4	0	42	140
2017	365	251	113	1	0	44	119
2016	366	259	104	3	0	43	129
2015	365	231	131	3	0	45	115
2014	365	199	165	1	0	49	105
2013	365	245	116	4	0	43	136
2012	366	271	77	18	4	41	200
2011	365	263	86	16	1	42	172
2010	304	170	113	21	4	48	182

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

Nearby counties on file

New Castle County5/yr
Kent County2/yr

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.