Hillsboro, Oregon, United States Historical Air Quality Analysis
Dive into detailed Air Quality Insights with historical data, monthly patterns, and yearly trends at your fingertips!
September Air Quality Analysis
Hillsboro, Oregon, United States
AQI Trends: Highest and Lowest
Same Day Analysis (27th September ):
On this day, AQI across the 5 years varied significantly: 2025 ranks 2nd highest AQI at 29 of Good air quality, showing improvement over 2022 on the same day.
Download 2024 Annual Data
World Air Quality Report

Day & Night AQI Trend: 27th Sep - 28th Sep 2025
Hillsboro, Oregon, United States
6 AM27th Sep 2025
7 PM
5 AM28th Sep 2025
47AQI
22AQI
50AQI
16AQI
In the last 24 hours,
Hillsboro's AQI reached its highest point of 50 at 1 AM during the Night, while the lowest point, 16, was recorded at 8 PM during the Night between 27th Sep and 28th Sep 2025.
Day & Night AQI Trend : Aug - Sep 2025
Hillsboro, Oregon, United States
--°C/°C
19°C13/26°C
20°C16/25°C
19°C15/23°C
23°C15/33°C
23°C18/33°C
24°C16/34°C
22°C17/29°C
19°C17/21°C
19°C17/23°C
20°C15/26°C
21°C17/25°C
19°C16/23°C
18°C15/21°C
17°C14/21°C
18°C12/28°C
17°C12/21°C
16°C10/25°C
23°C15/34°C
20°C15/27°C
19°C11/27°C
20°C12/30°C
19°C13/29°C
17°C13/23°C
17°C8/27°C
21°C11/33°C
22°C13/33°C
17°C11/25°C
16°C7/26°C
19°C9/30°C
18°C10/27°C
34AQI
25AQI
34AQI
28AQI
2025 Days Vs Air Quality
Hillsboro, Oregon, United States
97%
263
3%
7
Total number of days with different AQI categories in last 272 days in 2025 (93 days remaining)
Under WHO’s Safe Air Quality Limits: 97%
Health Risk Level:
Very Low
In 2025, 97% of 272 days were within WHO’s safe air quality limits. The risk of health issues is Very Low, but health impacts are still unclear.
Annual Air Quality Insights
Hillsboro, Oregon, United States
AQI levels in 2025
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
31AQI
28AQI
21AQI
18AQI
20AQI
21AQI
24AQI
29AQI
31AQI
28AQI
23AQI
28AQI
36AQI
38AQI
40AQI
43AQI
38AQI
42AQI
47AQI
31AQI
51AQI
52AQI
53AQI
44AQI
31AQI
29AQI
39AQI
49AQI
57AQI
67AQI
41AQI
19AQI
23AQI
22AQI
34AQI
25AQI
24AQI
25AQI
25AQI
29AQI
27AQI
23AQI
25AQI
23AQI
26AQI
40AQI
31AQI
17AQI
20AQI
19AQI
19AQI
23AQI
25AQI
16AQI
20AQI
17AQI
25AQI
25AQI
32AQI
36AQI
27AQI
20AQI
21AQI
24AQI
19AQI
27AQI
33AQI
34AQI
22AQI
38AQI
19AQI
16AQI
17AQI
17AQI
19AQI
18AQI
16AQI
18AQI
14AQI
14AQI
18AQI
18AQI
17AQI
20AQI
21AQI
16AQI
16AQI
15AQI
22AQI
16AQI
18AQI
17AQI
18AQI
20AQI
24AQI
28AQI
15AQI
13AQI
17AQI
20AQI
16AQI
17AQI
18AQI
20AQI
23AQI
21AQI
20AQI
20AQI
20AQI
16AQI
13AQI
14AQI
15AQI
19AQI
24AQI
22AQI
19AQI
14AQI
14AQI
15AQI
19AQI
21AQI
13AQI
14AQI
13AQI
19AQI
17AQI
15AQI
17AQI
16AQI
14AQI
15AQI
16AQI
17AQI
17AQI
17AQI
14AQI
13AQI
15AQI
11AQI
12AQI
13AQI
12AQI
15AQI
14AQI
13AQI
14AQI
16AQI
13AQI
15AQI
15AQI
14AQI
15AQI
17AQI
14AQI
15AQI
16AQI
17AQI
23AQI
25AQI
22AQI
24AQI
22AQI
17AQI
17AQI
18AQI
18AQI
17AQI
14AQI
15AQI
14AQI
11AQI
12AQI
14AQI
22AQI
24AQI
16AQI
15AQI
14AQI
17AQI
22AQI
19AQI
16AQI
14AQI
16AQI
19AQI
16AQI
19AQI
22AQI
15AQI
14AQI
17AQI
18AQI
19AQI
15AQI
21AQI
24AQI
31AQI
27AQI
20AQI
18AQI
23AQI
21AQI
21AQI
20AQI
18AQI
16AQI
19AQI
22AQI
19AQI
18AQI
21AQI
18AQI
16AQI
20AQI
26AQI
33AQI
19AQI
17AQI
18AQI
19AQI
27AQI
29AQI
38AQI
28AQI
16AQI
14AQI
13AQI
17AQI
17AQI
19AQI
17AQI
21AQI
27AQI
36AQI
49AQI
42AQI
54AQI
43AQI
34AQI
34AQI
30AQI
36AQI
25AQI
28AQI
50AQI
43AQI
49AQI
37AQI
23AQI
24AQI
22AQI
36AQI
36AQI
22AQI
34AQI
19AQI
19AQI
25AQI
32AQI
28AQI
30AQI
42AQI
25AQI
20AQI
29AQI
52AQI
22AQI
25AQI
29AQI
36AQI
24AQI
21AQI
18AQI
15AQI
17AQI
19AQI
27AQI
31AQI
No. of days
202523AQI
Highest AQI recorded in
January36AQI
Lowest AQI recorded in
May15AQI
202421AQI
Highest AQI recorded in
December32AQI
Lowest AQI recorded in
June13AQI
202325AQI
Highest AQI recorded in
November41AQI
Lowest AQI recorded in
April15AQI
202229AQI
Highest AQI recorded in
October54AQI
Lowest AQI recorded in
June14AQI
202123AQI
Highest AQI recorded in
January33AQI
Lowest AQI recorded in
May14AQI
202032AQI
Highest AQI recorded in
September87AQI
Lowest AQI recorded in
June13AQI
Most & Least Polluted Years Over the Last 6 Years
Hillsboro's annual 2025 AQI (23) shows an average percentage change of -8.1% (improved AQI) compared to previous years: 2020 (32), 2021 (23), 2022 (29), 2023 (25), 2024 (21).