Half Moon Bay, California, United States Historical Air Quality Analysis
Dive into detailed Air Quality Insights with historical data, monthly patterns, and yearly trends at your fingertips!
October Air Quality Analysis
Half Moon Bay, California, United States
AQI Trends: Highest and Lowest
Same Day Analysis (18th October ):
On this day, AQI across the 3 years varied significantly: 2025 ranks 1st highest AQI at 60 of Moderate air quality on the same day.
Download 2024 Annual Data
World Air Quality Report

Day & Night AQI Trend: 18th Oct - 19th Oct 2025
Half Moon Bay, California, United States
7 AM18th Oct 2025
6 PM
6 AM19th Oct 2025
73AQI
53AQI
73AQI
55AQI
In the last 24 hours,
Half Moon Bay's AQI reached its highest point of 73 at 1 PM during the Day, while the lowest point, undefined, was recorded at 6 AM during the Night between 18th Oct and 19th Oct 2025.
Day & Night AQI Trend : Sep - Oct 2025
Half Moon Bay, California, United States
17°C15/21°C
17°C15/20°C
16°C14/19°C
16°C14/21°C
20°C13/31°C
21°C16/27°C
18°C15/21°C
17°C14/21°C
16°C13/19°C
17°C16/20°C
18°C16/22°C
18°C17/19°C
19°C17/22°C
17°C15/19°C
16°C14/18°C
16°C13/20°C
16°C14/20°C
19°C13/28°C
16°C14/19°C
17°C14/21°C
17°C16/19°C
16°C12/20°C
16°C12/22°C
15°C11/22°C
14°C10/17°C
12°C9/16°C
14°C11/18°C
13°C10/18°C
15°C10/21°C
16°C11/24°C
--°C/°C
47AQI
40AQI
50AQI
42AQI
2025 Days Vs Air Quality
Half Moon Bay, California, United States
95%
277
5%
14
Total number of days with different AQI categories in last 292 days in 2025 (73 days remaining)
Under WHO’s Safe Air Quality Limits: 95%
Health Risk Level:
Very Low
In 2025, 95% of 292 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
Half Moon Bay, California, United States
AQI levels in 2025
Jan.
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
48AQI
42AQI
42AQI
34AQI
33AQI
31AQI
25AQI
26AQI
36AQI
41AQI
36AQI
26AQI
34AQI
31AQI
44AQI
49AQI
45AQI
51AQI
51AQI
43AQI
42AQI
47AQI
46AQI
56AQI
46AQI
43AQI
42AQI
40AQI
37AQI
38AQI
37AQI
34AQI
22AQI
22AQI
23AQI
29AQI
26AQI
25AQI
25AQI
29AQI
28AQI
27AQI
24AQI
26AQI
31AQI
31AQI
26AQI
23AQI
24AQI
25AQI
25AQI
27AQI
30AQI
33AQI
26AQI
26AQI
28AQI
32AQI
40AQI
33AQI
27AQI
23AQI
25AQI
25AQI
26AQI
31AQI
31AQI
33AQI
28AQI
28AQI
27AQI
24AQI
31AQI
53AQI
33AQI
20AQI
24AQI
32AQI
26AQI
23AQI
24AQI
34AQI
25AQI
29AQI
33AQI
19AQI
23AQI
19AQI
28AQI
24AQI
24AQI
22AQI
20AQI
27AQI
26AQI
19AQI
17AQI
30AQI
21AQI
21AQI
19AQI
28AQI
36AQI
29AQI
27AQI
28AQI
23AQI
26AQI
29AQI
25AQI
30AQI
34AQI
41AQI
30AQI
19AQI
20AQI
21AQI
28AQI
32AQI
37AQI
36AQI
28AQI
23AQI
36AQI
36AQI
49AQI
42AQI
25AQI
29AQI
27AQI
22AQI
17AQI
17AQI
32AQI
38AQI
37AQI
32AQI
35AQI
43AQI
29AQI
45AQI
34AQI
24AQI
27AQI
20AQI
18AQI
23AQI
23AQI
17AQI
26AQI
42AQI
49AQI
44AQI
40AQI
50AQI
28AQI
23AQI
20AQI
18AQI
17AQI
21AQI
36AQI
42AQI
42AQI
40AQI
41AQI
34AQI
33AQI
33AQI
40AQI
38AQI
32AQI
33AQI
32AQI
23AQI
20AQI
22AQI
30AQI
32AQI
25AQI
20AQI
21AQI
21AQI
30AQI
27AQI
29AQI
29AQI
24AQI
19AQI
17AQI
19AQI
28AQI
29AQI
25AQI
19AQI
17AQI
19AQI
17AQI
17AQI
18AQI
20AQI
21AQI
14AQI
14AQI
15AQI
15AQI
14AQI
15AQI
18AQI
22AQI
21AQI
22AQI
22AQI
19AQI
29AQI
33AQI
28AQI
33AQI
24AQI
29AQI
32AQI
26AQI
28AQI
28AQI
23AQI
20AQI
34AQI
18AQI
14AQI
19AQI
22AQI
28AQI
41AQI
47AQI
36AQI
26AQI
32AQI
36AQI
40AQI
37AQI
28AQI
32AQI
36AQI
31AQI
39AQI
32AQI
29AQI
27AQI
30AQI
22AQI
21AQI
17AQI
17AQI
27AQI
27AQI
29AQI
20AQI
20AQI
29AQI
28AQI
32AQI
36AQI
36AQI
30AQI
31AQI
36AQI
43AQI
43AQI
49AQI
55AQI
46AQI
44AQI
30AQI
33AQI
40AQI
43AQI
55AQI
57AQI
54AQI
53AQI
54AQI
51AQI
48AQI
50AQI
44AQI
50AQI
43AQI
46AQI
55AQI
56AQI
60AQI
40AQI
27AQI
28AQI
26AQI
30AQI
32AQI
21AQI
29AQI
32AQI
50AQI
No. of days
202531AQI
Highest AQI recorded in
October50AQI
Lowest AQI recorded in
July21AQI
202433AQI
Highest AQI recorded in
December43AQI
Lowest AQI recorded in
March13AQI
202336AQI
Highest AQI recorded in
November48AQI
Lowest AQI recorded in
December35AQI
202231AQI
Highest AQI recorded in
August65AQI
Lowest AQI recorded in
September30AQI
202165AQI
Highest AQI recorded in
August113AQI
Lowest AQI recorded in
May26AQI
202064AQI
Highest AQI recorded in
October104AQI
Lowest AQI recorded in
November48AQI
Most & Least Polluted Years Over the Last 6 Years
Half Moon Bay's annual 2025 AQI (31) shows an average percentage change of -25.6% (improved AQI) compared to previous years: 2020 (64), 2021 (65), 2022 (31), 2023 (36), 2024 (33).