City report · California, United States
San Mateo Air quality today
Air quality in San Mateo currently reads AQI 37 (Good): Air quality is satisfactory for everyone.
Air quality right now
AQI 37
Good
- PM2.5, fine particles (µg/m³)
- 6.6
- tree cover
- 29.6%
- trees in this area
- 93.0K
- more trees needed
- 1.3K
Measured across a 1.2 mi (2 km) radius around Downtown, San Mateo, CA, USA (4.9 sq mi), from a satellite image of Sep 12, 2026. Lower AQI is better: 0–50 is Good, above 300 is Hazardous.
San Mateo · AQI 37 (Good)
San Mateo's tree count comes to 92,991 trees across 4.9 sq mi (12.57 km²), 0 points below the 30% tree-cover level considered healthy for this area, so roughly 1,257 more trees would close the gap.
Air quality detail
Air quality in San Mateo today: AQI 37, Good
Main pollutant: PM2.5 · Observed Nov 11, 07:00 local time via OpenAQ ground stations, US EPA index. Values in µg/m³.
Ground station · Idaho St. San Mateo, 0.8 mi (1.3 km) away · median of 9 stations
Health signal
Air quality is satisfactory for everyone.
PM2.5
6.6
PM10
—
NO₂
—
O₃
—
SO₂
—
CO
—
Data: OpenAQ · AirGradient, Clarity, Charles Roman, KO, Felix and Gene, Jersey Giant
- Outdoor exercise
- A good day to be active outside
- Windows
- Open them to air the house
- Mask
- Not needed
- Air purifier
- Not needed
Over the last 7 days, the CAMS air-quality model put San Mateo's daily AQI at 48 on average, from 34 on Nov 8 to an hourly peak of 77 on Nov 7.
Where San Mateo stands: the most polluted cities in the world right now · the cleanest
Tree cover detail
Tree cover in San Mateo: Below target
29.6% tree cover against a 30% healthy-neighborhood target, across 4.9 sq mi (12.57 km²).
Trees in this area
92,991
Target trees
94,248
More trees needed
1,257
CO₂ if planted / yr
27.7 t
Deforestation · 2001–2025
How much forest has San Mateo lost?
Since 2001, the area within 10 km of San Mateo has lost about 453 acres (183 hectares) of forest (about 340 football fields): 2.2% of the forest it had in 2000. Most of it (56%) was deforestation, forest cleared for good, mainly for towns and roads.
2017: satellite photo from July 2017 of a 5 × 5 km area in the city center.
- Forest lost since 2001
- 453 acres (183 ha)about 340 football fields
- Share of its forest
- 2.2%of what there was in 2000
- Cleared for good
- 256 acres (103 ha)deforestation: turned into farms, mines or towns
The worst year was 2017, when about 41 acres (17 hectares) of forest were lost.
Acres of forest lost each year
Show the figures as a table
| Year | Cleared for good | Can grow back | Total |
|---|---|---|---|
| 2001 | 20 acres (8 ha) | 4 acres (2 ha) | 24 acres (10 ha) |
| 2002 | 10 acres (4 ha) | under 1 ha | 13 acres (5 ha) |
| 2003 | 8 acres (3 ha) | 3 acres (1 ha) | 11 acres (4 ha) |
| 2004 | 14 acres (6 ha) | 5 acres (2 ha) | 20 acres (8 ha) |
| 2005 | 11 acres (5 ha) | 10 acres (4 ha) | 22 acres (9 ha) |
| 2006 | 18 acres (7 ha) | 10 acres (4 ha) | 28 acres (11 ha) |
| 2007 | 14 acres (6 ha) | 3 acres (1 ha) | 17 acres (7 ha) |
| 2008 | 9 acres (4 ha) | 20 acres (8 ha) | 28 acres (12 ha) |
| 2009 | 16 acres (7 ha) | 20 acres (8 ha) | 37 acres (15 ha) |
| 2010 | 10 acres (4 ha) | 6 acres (2 ha) | 15 acres (6 ha) |
| 2011 | 25 acres (10 ha) | 9 acres (4 ha) | 34 acres (14 ha) |
| 2012 | 12 acres (5 ha) | 10 acres (4 ha) | 22 acres (9 ha) |
| 2013 | 7 acres (3 ha) | 8 acres (3 ha) | 15 acres (6 ha) |
| 2014 | 14 acres (6 ha) | 5 acres (2 ha) | 19 acres (8 ha) |
| 2015 | 8 acres (3 ha) | under 1 ha | 9 acres (4 ha) |
| 2016 | 10 acres (4 ha) | 12 acres (5 ha) | 22 acres (9 ha) |
| 2017 | 17 acres (7 ha) | 24 acres (10 ha) | 41 acres (17 ha) |
| 2018 | 5 acres (2 ha) | under 1 ha | 6 acres (3 ha) |
| 2019 | under 1 ha | under 1 ha | 3 acres (1 ha) |
| 2020 | 8 acres (3 ha) | under 1 ha | 9 acres (4 ha) |
| 2021 | 4 acres (2 ha) | 7 acres (3 ha) | 12 acres (5 ha) |
| 2022 | 4 acres (2 ha) | 17 acres (7 ha) | 21 acres (9 ha) |
| 2023 | 6 acres (2 ha) | 4 acres (2 ha) | 10 acres (4 ha) |
| 2024 | 3 acres (1 ha) | under 1 ha | 4 acres (2 ha) |
| 2025 | under 1 ha | 12 acres (5 ha) | 13 acres (5 ha) |
What is causing deforestation around San Mateo?
- Towns and roadscleared for good49% · 222 acres (90 ha)
- Loggingcan grow back29% · 133 acres (54 ha)
- Storms, floods and other natural causescan grow back4.8% · 22 acres (9 ha)
Also: mining and energy, farms, pasture and plantations, unknown causes.
Causes for 2025 are estimates, based on what caused forest loss in the same places up to 2024.
Forest gained and lost, 2000–2020
- Forest in 2000
- 26,800 acres (10,900 ha)
- Forest in 2020
- 27,200 acres (11,000 ha)
- Overall change
- +358 acres (145 ha)more forest than in 2000
Comparing satellite maps from 2000 and 2020, the forest around San Mateo stayed about the same size, at about 27,200 acres (11,000 hectares): new forest grew on about 534 acres (216 hectares), and about 175 acres (71 hectares) were lost.
These 2000 and 2020 maps, from the University of Maryland, count any land with trees taller than 5 m as forest, including plantations and orchards. Forest that was cut or burned and had grown back by 2020 counts in both years, so the loss here is smaller than the yearly figures.
These figures cover everything within 10 km of the city center, a wider area than the report above, because forest is usually lost at a city's edges.
Source: Hansen/UMD/Google/USGS/NASA, Global Forest Change (GFC-2025-v1.13); causes: WRI/Google DeepMind drivers of forest loss; both CC BY 4.0, summed by Airleaf for each area. Forest gained and lost 2000–2020: Potapov et al. 2022, UMD GLAD Global Land Cover and Land Use Change, CC BY 4.0. Images: contains modified Copernicus Sentinel data. How it's measured
In the same region
Measured cities near San Mateo
Same 2 km radius, same index — so they compare directly.
- Daly City19.9 km
United States
- Tree cover
- 17%
- Air quality
- 55
- Hayward24.6 km
United States
- Tree cover
- 20%
- Air quality
- 29
- San Francisco25.0 km
United States
- Tree cover
- 6%
- Air quality
- 51
- Oakland27.3 km
United States
- Tree cover
- 7%
- Air quality
- 31
- Fremont29.7 km
United States
- Tree cover
- 15%
- Air quality
- 29
- Sunnyvale33.4 km
United States
- Tree cover
- 19%
- Air quality
- 21
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Frequently asked
Questions about San Mateo
What is the air quality (AQI) in San Mateo right now?
The latest reading for San Mateo shows an AQI of 37 (Good), measured Nov 11, 07:00 local time by 9 ground monitoring stations via OpenAQ (the median of their readings; the nearest is Idaho St. San Mateo, 0.8 mi (1.3 km) away). The main pollutant is PM2.5. Air quality is satisfactory for everyone.
Is it safe to exercise outside in San Mateo today?
At AQI 37 (Good): a good day to be active outside. Windows: open them to air the house. Masks: not needed. The reading changes through the day, so check again before a long run or ride.
What has the air quality in San Mateo been like this week?
Over the last 7 days, the CAMS air-quality model put San Mateo's daily AQI at 48 on average, from 34 on Nov 8 to an hourly peak of 77 on Nov 7. No day averaged above 100, the level where the air turns unhealthy for sensitive groups.
How much forest has the area around San Mateo lost since 2001?
Since 2001, the area within 10 km of San Mateo has lost about 453 acres (183 hectares) of forest (about 340 football fields): 2.2% of the forest it had in 2000. Most of it (56%) was deforestation, forest cleared for good, mainly for towns and roads. Comparing satellite maps from 2000 and 2020, the forest around San Mateo stayed about the same size, at about 27,200 acres (11,000 hectares): new forest grew on about 534 acres (216 hectares), and about 175 acres (71 hectares) were lost.
What is the tree count in San Mateo?
San Mateo has an estimated 92,991 trees across the 4.9 sq mi (12.57 km²) measured — 29.6% tree cover, 0 percentage points short of the 30% tree-cover target set for this area.
How many more trees does San Mateo need?
San Mateo needs roughly 1,257 more trees to close a 0-point shortfall against its 30% tree-cover target — about 27.7 t of extra CO₂ absorbed per year once grown.
How are San Mateo's air quality and tree cover measured?
Air quality is measured by ground monitoring stations near Downtown, via OpenAQ; the 7-day trend is the Open-Meteo / CAMS model's estimate. Tree cover is measured from Sentinel-2 L2A (ESA Copernicus) via Earth Search satellite imagery at 10 m detail across a 1.2 mi (2 km) radius around Downtown; the tree count is an estimate derived from that cover.
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