Worsening alerts use US AQI equivalents calculated from hourly PM2.5. Confirmed improvements require a clear move below a category boundary across fresh readings, so small back-and-forth changes do not keep triggering alerts. Quiet hours suppress messages. The morning briefing can include your saved Simple or Detailed routine; set that up for a more useful estimate. A current NEA forecast is included when available and is labeled PSI if that is what NEA publishes. PSI forecasts are not converted into PM2.5 forecasts.

Background delivery requires an enabled subscription and a connected scheduled service. Your device, connection and Focus settings can affect arrival time. Alert preferences are stored separately from your calculator settings and subscription, so later customization will not require reinstalling or granting permission again.

Assumes 30% of outdoor PM2.5 in filtered rooms and 50% in other enclosed rooms, with windows closed. Time out and about assumes the outdoor PM2.5 level, including shopping, activities and outdoors. These are adjustable assumptions, not indoor measurements. Home fills the hours remaining in a 24-hour day. The selected outdoor reading is held constant, and exposure is calculated as a time-weighted average. Choose “Refine your estimate” to enter more detailed settings.

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

In the calculator, each small bar’s color follows its PM2.5 concentration. Its length shows its share of your total estimated exposure, including time, masking and activity factors.

Exposure combines how polluted the air is with how long you spend breathing it. The calculator adds up PM2.5 × hours for each place and divides by 24. One hour at 100 µg/m³ contributes the same to this estimate as two hours at 50 µg/m³. It estimates an average concentration across your day, not the particles your lungs absorb. The selected outdoor reading is held constant for the scenario.

The original calculator uses 50% as a starting assumption for indoor air with closed windows and no effective filtration. Actual indoor PM2.5 depends on gaps, ventilation, indoor sources and filtration. The transport default is also only an assumption: outside air entry and cabin filtration matter. Use an indoor or vehicle monitor to replace these assumptions with readings when possible.

No. PM2.5 is a particle concentration in µg/m³. PSI is Singapore’s pollution index, while US AQI uses a different index scale. Always check the pollutant, scale and averaging period before comparing numbers. A PSI of 100 does not mean 100 µg/m³ or a US AQI of 100.

No. This site applies US EPA PM2.5 breakpoints directly to the selected 1-hour concentration for comparison. Official daily PM2.5 AQI uses a 24-hour concentration basis; AirNow’s current AQI uses a NowCast based on multiple recent hours. This site does not calculate either official measure. Its category labels use US EPA bands, rather than NEA’s 1-hour PM2.5 bands.

NEA’s 24-hour PSI combines sub-indices for six pollutants and reports the highest. Its PM2.5 component looks back over the preceding 24 hours. Earlier clean hours can smooth out a new spike, and earlier polluted hours can keep PSI elevated after the air improves. An hourly update does not make it a 1-hour measurement.

For PM2.5, the original site includes children and teenagers, older adults, and people with heart or lung disease, including asthma. Pregnancy is also a reason to take extra care with smoke exposure. Children count even if they are healthy. “Unhealthy for sensitive groups” does not only mean people who already feel ill.

No. The original site explains that “Moderate” is not risk-free, and “Good” is a lower-concern ambient-air category rather than a guarantee of zero risk. Compare like with like: one hour at a particular concentration is not the same as a full-day average at that concentration.

No. This is an independent educational and scenario-planning tool, not an official air-quality service or a personal health-risk assessment. Indoor concentrations and mask reductions may be assumptions rather than measurements. The estimate cannot establish whether recess or another activity is safe for a particular child. Follow official guidance and consult an appropriate healthcare professional for individual health concerns.