EPA monitor data through 2025 · Updated August 13, 2026 · Methods
In 2025, Chambersburg-Waynesboro, PA recorded 0 days above an Air
Quality Index of 100, the level at which EPA begins warning sensitive groups, out
of 302 days with monitoring data. Most of those bad days were driven by
ozone and fine particles equally. Under the AQI rules that applied before 2013, the same air would have
scored 0 days.
Unhealthy days, 2025
0
AQI above 100
Same air, pre-2013 rules
0
for comparison with older reports
Good-air days
277
AQI 50 or below
Days monitored
302
partial coverage
Unhealthy days by year, scored two ways
EPA changed what an AQI of 100 means in 2013 and again in 2015, so a count published before those
changes is not comparable to one published after. Each panel below applies a single fixed rulebook to
every year, so each is internally consistent.
Why this matters.
Scored by today's rules
Scored by the pre-2013 rules
Faded columns mark years with fewer than
300 monitored days, where the count is not comparable.
What 2025 looked like
Air quality category
Days
Share of monitored days
Good
277
92%
Moderate
25
8%
Unhealthy for sensitive groups
0
0%
Unhealthy or worse
0
0%
Median AQI 37 · 90th-percentile AQI 49 · worst day
87. Scored under current rules.
