Lancaster County, Pennsylvania air quality history
Daily Air Quality Index summaries from EPA monitors in Lancaster, Pennsylvania, 1980–2025.
61%
Good days in 2025
45
Median daily AQI, 2025
2
Days above 100 in 2025
365
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Lancaster, Pennsylvania on 365 days. 221 of those days (61%) were in the Good range, and the median daily AQI was 45. That median is higher than the typical monitored county in Pennsylvania (median 40 across 38 counties), and higher than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 195 days. Across the years with fuller monitoring, the share of Good days fell: an average of 73% in 1980–1982 versus 47% in 2023–2025.
How the days broke down each year
Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.
Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous
Typical and high-end AQI over time
The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.
Median daily AQI
90th-percentile daily AQI
Main pollutant by day, 2025
On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.
Pollutant
Days as main pollutant
Share of monitored days
Fine particles (PM2.5)
195
53%
Ozone
170
47%
Year-by-year data
Annual AQI summary by year
Year
Days with AQI
Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous
Median AQI
90th pct.
Max AQI
Main pollutant
2025
365
221
142
2
0
0
0
45
71
119
PM2.5
2024
366
189
174
3
0
0
0
50
69
125
PM2.5
2023
365
108
243
9
3
1
1
58
85
321
PM2.5
2022
365
84
274
6
1
0
0
59
80
153
PM2.5
2021
365
100
257
7
1
0
0
56
82
156
PM2.5
2020
366
177
184
4
1
0
0
51
66
153
PM2.5
2019
365
160
195
9
1
0
0
52
76
159
PM2.5
2018
365
167
193
5
0
0
0
52
75
126
PM2.5
2017
365
122
239
4
0
0
0
55
71
128
PM2.5
2016
366
117
243
6
0
0
0
56
76
136
PM2.5
2015
365
121
234
10
0
0
0
56
85
140
PM2.5
2014
365
58
292
14
1
0
0
61
85
155
PM2.5
2013
365
152
205
8
0
0
0
54
77
142
PM2.5
2012
366
96
250
19
1
0
0
60
87
179
PM2.5
2011
365
93
252
17
3
0
0
60
90
161
PM2.5
2010
365
149
188
26
2
0
0
54
94
174
PM2.5
2009
365
138
223
4
0
0
0
54
79
128
PM2.5
2008
366
230
119
17
0
0
0
43
80
143
Ozone
2007
365
217
112
35
1
0
0
44
100
166
Ozone
2006
365
229
109
23
4
0
0
43
93
169
Ozone
2005
365
202
119
40
4
0
0
45
108
177
Ozone
2004
366
224
126
15
1
0
0
43
87
182
Ozone
2003
365
221
120
20
2
2
0
43
90
217
Ozone
2002
365
207
113
26
18
1
0
44
105
214
Ozone
2001
365
202
119
29
15
0
0
46
108
200
Ozone
2000
366
231
111
19
4
1
0
41
87
201
Ozone
1999
365
224
101
23
14
3
0
43
108
213
Ozone
1998
365
254
58
27
25
1
0
38
122
201
Ozone
1997
365
283
44
18
17
3
0
37
101
217
Ozone
1996
366
273
61
29
3
0
0
39
97
174
Ozone
1995
358
267
51
24
14
2
0
38
108
209
Ozone
1994
363
260
64
33
5
1
0
42
101
201
NO2
1993
365
259
64
30
11
1
0
37
108
208
Ozone
1992
366
303
45
14
4
0
0
35
77
179
Ozone
1991
364
257
60
31
15
1
0
40
122
202
Ozone
1990
363
299
39
21
4
0
0
37
74
164
Ozone
1989
365
300
50
14
1
0
0
35
67
166
NO2
1988
365
264
50
21
26
4
0
40
136
206
NO2
1987
364
261
60
25
18
0
0
42
112
200
NO2
1986
365
301
45
15
4
0
0
38
71
179
NO2
1985
364
276
62
20
6
0
0
38
87
182
NO2
1984
364
270
67
20
7
0
0
40
78
195
NO2
1983
363
270
52
17
18
6
0
37
112
213
NO2
1982
355
237
81
28
6
3
0
43
101
279
NO2
1981
352
269
53
15
13
2
0
38
87
229
NO2
1980
347
259
57
23
6
2
0
38
100
205
NO2
What this data can and can’t tell you
It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.
It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.
Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.
Counties in Pennsylvania with a similar median AQI in 2025
