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Estimated exposure

—

µg/m³-equivalent

Waiting for reading

Home

Hours at home

—h

Indoor PM2.5

µg/m³

0250 µg/m³

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% of outdoors

0100 %

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Time at home fills automatically · windows closed.

School or Work

Hours at school or workHours at school or workh

Indoor PM2.5

µg/m³

0250 µg/m³

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% of outdoors

0100 %

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Lock either value if you want to hold it. The other updates automatically.

Planned outdoor recessPlanned outdoor recessmin

School moves recess indoors atµg/m³

Indoor Activities

Time at activitiesTime at activitiesmin

Indoor PM2.5

µg/m³

0250 µg/m³

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% of outdoors

0100 %

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Lock either value if you want to hold it. The other updates automatically.

Time in an enclosed setting away from home or school.

Outdoors^†

Walking outdoorsWalking outdoorsmin

Masking while walking² Not wearing a mask Wearing an N95 or equivalent Wearing a surgical mask

Assumed reduction

0100 %

— µg/m³ after mask

Moderate exerciseModerate exercisemin

Vigorous exerciseVigorous exercisemin

Outside school or work

Transportation

Time in a vehicleTime in a vehiclemin

% of outdoors

0100 %

Time in a vehicle per day.

Your estimated exposure

Waiting for an outdoor reading

—µg/m³-equivalent

24hr estimate based on your settings

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Notes & assumptions

Movement makes you breathe more deeply and quickly, increasing the volume of air inhaled at the same PM2.5 concentration. The calculator uses sitting as 1×, walking as 2×, moderate exercise as 5× and vigorous exercise as 10×. These are illustrative scenario assumptions, not measured individual breathing rates. The comparison below uses one unmasked hour outside at a constant PM2.5 concentration. These model breathing more air, not a higher outdoor concentration. Exposure = minutes × effective PM2.5 × activity factor ÷ 1,440. This is an inhaled-exposure model, not a measured PM2.5 concentration or a health-risk score. “Relatively low” does not mean risk-free. About breathing rate and exposure
70% for an N95 and 20% for a surgical mask are editable assumptions, not guaranteed protection. The mask setting applies only to walking. Recess and exercise use the unmasked outdoor reading unless recess is moved indoors. For children, consider a lower reduction: gaps, movement and inconsistent wear may reduce protection. There is no single validated child-fit discount. About mask fit
The recess trigger is your school’s chosen PM2.5 rule, not an official recommendation. At or above it, planned recess uses the school’s indoor PM2.5. Recess stays within school hours; home fills the remaining day. Count each activity only once. Outdoor air is held constant across the scenario.
WHO ambient-air guidelines: 15 µg/m³ for a 24-hour average and 5 µg/m³ for an annual average. Ambient guidelines are not personal-exposure safety thresholds. The daily guideline uses the 99th percentile of daily averages.
AQI equivalents use US EPA PM2.5 breakpoints applied to the entered concentration; they are not official US AQI, NowCast or Singapore PSI.
Transportation uses only a percentage of outdoor PM2.5. For the other indoor settings, PM2.5 and percentage inputs change together. Locks are optional. A PM2.5 lock holds the concentration when outdoor air changes; a percentage lock holds its relationship to outdoor air.