Armstrong County, Pennsylvania air quality history
Daily Air Quality Index summaries from EPA monitors in Armstrong, Pennsylvania, 1997–2025.
71%
Good days in 2025
41
Median daily AQI, 2025
0
Days above 100 in 2025
363
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Armstrong, Pennsylvania on 363 days. 256 of those days (71%) were in the Good range, and the median daily AQI was 41. That median is about the same as the typical monitored county in Pennsylvania (median 40 across 38 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 189 days. Across the years with fuller monitoring, the share of Good days rose: an average of 60% in 1998–2000 versus 71% in 2023–2025.
Years with fewer than 120 monitored days (1997) are shown in the table but left out of comparisons and trend statements.
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
Ozone
189
52%
Fine particles (PM2.5)
174
48%
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
363
256
107
0
0
0
0
41
61
96
Ozone
2024
365
275
89
1
0
0
0
41
59
108
Ozone
2023
362
238
117
4
1
2
0
44
71
210
PM2.5
2022
365
198
165
2
0
0
0
48
63
122
PM2.5
2021
350
184
165
1
0
0
0
48
70
108
PM2.5
2020
366
246
117
3
0
0
0
43
58
122
PM2.5
2019
365
261
104
0
0
0
0
43
57
72
PM2.5
2018
360
245
114
1
0
0
0
42
61
143
PM2.5
2017
361
182
179
0
0
0
0
50
67
93
PM2.5
2016
365
157
203
5
0
0
0
53
69
119
PM2.5
2015
364
141
220
3
0
0
0
53
71
115
PM2.5
2014
364
137
225
2
0
0
0
53
69
119
PM2.5
2013
360
127
226
6
1
0
0
53
74
174
PM2.5
2012
366
176
175
14
1
0
0
51
71
159
PM2.5
2011
361
143
214
4
0
0
0
54
72
115
PM2.5
2010
353
113
232
7
1
0
0
56
80
156
PM2.5
2009
273
142
126
5
0
0
0
49
71
133
PM2.5
2008
214
143
54
16
1
0
0
44
93
154
Ozone
2007
213
134
53
23
3
0
0
45
108
187
Ozone
2006
214
146
55
11
2
0
0
43
87
190
Ozone
2005
214
130
56
24
3
1
0
47
108
204
Ozone
2004
214
152
44
18
0
0
0
44
97
150
Ozone
2003
212
142
54
12
3
1
0
44
97
208
Ozone
2002
212
130
48
19
14
1
0
45
133
210
Ozone
2001
211
114
56
26
13
2
0
47
126
213
Ozone
2000
210
162
35
11
2
0
0
39
80
182
Ozone
1999
210
104
65
23
17
1
0
51
136
202
Ozone
1998
210
110
51
29
20
0
0
50
150
195
Ozone
1997
66
57
9
0
0
0
0
32
61
90
Ozone
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
