Diamond Bar pollen forecast - today, tomorrow and the week ahead
Pollen Today
Today (20 September) pollen in Diamond Bar is high; grass and ragweed are high; mugwort is low.
Pollen Tomorrow
Tomorrow (21 September 2026) ragweed remains high, grass declining, mugwort no longer expected.
7-Day Trend
Over the next week grass, mugwort, and ragweed will increase.
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Pollen Risk
Today - 20 September
| Pollen species | Level | Value |
|---|---|---|
| Alder (Alnus) | None | 0/100 |
| Birch (Betula) | None | 0/100 |
| Hazel (Corylus) | None | 0/100 |
| Cypress (Cupressaceae) | None | 0/100 |
| Grass (Poaceae) | High | 55/100 |
| Willow (Salicaceae) | None | 0/100 |
| Mugwort (Artemisia) | Low | 12/100 |
| Ragweed (Ambrosia) | High | 70/100 |
Tomorrow - 21 September
| Pollen species | Level | Value | 7-Day Trend |
|---|---|---|---|
| Alder (Alnus) | None | 0/100 | — |
| Birch (Betula) | None | 0/100 | — |
| Hazel (Corylus) | None | 0/100 | — |
| Cypress (Cupressaceae) | None | 0/100 | — |
| Grass (Poaceae) | Moderate | 37/100 | |
| Willow (Salicaceae) | None | 0/100 | — |
| Mugwort (Artemisia) | None | 0/100 | |
| Ragweed (Ambrosia) | High | 57/100 |
Local Environmental Conditions
Diamond Bar's eastern Los Angeles County Pomona Valley foothill setting features walnut, oak, and toyon as the main tree pollen sources, with the Southern California Black Walnut woodlands being a particularly distinctive and locally significant native pollen source. Exposure varies between the walnut woodland-covered hillsides and the more built-up commercial corridors along Diamond Bar Boulevard, while the Puente Hills topography creates downslope wind conditions that concentrate pollen in valley floor areas.
Diamond Bar's eastern Los Angeles County setting produces a season opening in January with olive and walnut before grass from surrounding Pomona Valley land peaks through March and April. Mugwort extends exposure into September, while the inland foothill setting means higher temperatures than in coastal cities and the Puente Hills backdrop concentrates pollen under certain downslope wind conditions throughout the season.
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Frequently Asked Questions About Pollen in California
Is pollen high in Diamond Bar right now?
On 20 September 2026, overall pollen levels in Diamond Bar are high. Ambrosia is the main contributor to airborne pollen, while grass and artemisia remain at lower levels
Will pollen levels change in Diamond Bar tomorrow?
On 21 September 2026, pollen conditions in Diamond Bar will be different from today, with ambrosia at high levels and grass continuing to decline
Is pollen expected to decrease in Diamond Bar this week?
According to the five-day outlook, ambrosia, artemisia, and grass pollen levels will increase later in the week.
Which pollen types are currently active in Diamond Bar?
On 20 September 2026, Ambrosia is the dominant pollen source in Diamond Bar. grass and artemisia are also present but at lower levels.
When is pollen season in Diamond Bar?
How often is the Diamond Bar pollen forecast updated?
The Diamond Bar pollen forecast is updated four times daily. See the timestamp below for the most recent update.
Does pollen in Diamond Bar come from nearby or far away?
Studies show that most pollen exposure (often 70–90%) comes from nearby sources, such as local trees and vegetation. A good pollen forecast therefore depends on accurately representing local vegetation. Pollen can travel long distances, but this usually matters only early in the season or during specific wind events.
Are pollen levels in Diamond Bar based on measurements or forecasts?
Pollen data is often misunderstood. Most "pollen levels" are not real-time measurements, but forecasts.
Direct pollen measurements are typically delayed by 1-2 days because they require manual analysis. To show current conditions in Diamond Bar, modern forecasts combine recent measurements, weather data, and information about local vegetation.
This allows us to estimate pollen levels for today and the coming days, not just report the past.
Airmine’s atmospheric monitoring platform was developed with support from the European Space Agency (ESA)’s Business Applications and Space Solutions (BASS) team, using satellite and Earth observation technologies to improve emissions monitoring.
Understanding the Scale
The 0–100 scores represent risk levels, not direct measurements of pollen or air pollutant concentrations. Higher scores indicate higher risk. Pollen and air quality use different thresholds.
Pollen
| None | 0 | No or negligible risk of exposure. Pollen/mold exposure is expected to be minimal. |
| Low | 0-25 | Low risk of exposure. Small amounts of pollen or mold spores may be present. |
| Moderate | 25-50 | Moderate risk of exposure. Pollen/mold exposure is expected to be noticeable. |
| High | 50-75 | High risk of exposure. Elevated pollen/mold exposure is expected. |
| Very High | 75-100 | Very high risk of exposure. Pollen/mold exposure is expected to be at or near its highest levels. |
Get More in the Airmine Pollen app
Get 15-day pollen forecasts with morning, afternoon and evening detail, plus 5-day air quality forecasts. Explore interactive pollen risk maps, estimated pollen season start, route profiles and a symptoms diary.
Features and forecast availability vary by region. Currently covering Europe, the contiguous US, southern Canada, South Africa, Australia, Indonesia (Java & Bali), Brazil, Paraguay, Uruguay and the Buenos Aires area.
Developed with support from the European Space Agency (ESA) Business Applications and Space Solutions (BASS).
