Monte Carlo simulation to control indoor pollutants from indoor and outdoor sources for residential buildings in Tianjin, China

The indoor air quality (IAQ) impacts occupants' health significantly. It is important to know the actual IAQ under different source strengths and occupants' air purifier usage strategies. To achieve this goal, we conducted a Monte Carlo simulation to calculate the indoor pollutant concentrations under different conditions. It is confirmed that our simulation is reliable by comparing the simulation results with actual measurement results. According to the simulation results, we found that indoor nighttime CO2, formaldehyde and PM2.5 were lowest in summer. In spring and winter, the nightly indoor CO2 concentration should be kept below 1000 ppm for F3 homes (formaldehyde semission rate: 0.03-0.06 mg/(m(2).h)) and below 900 ppm for F4 homes (formaldehyde emission rate: 0.06-0.12 mg/(m(2).h)) to ensure that the nighttime formaldehyde concentration is lower than 80 mu g/m(3) for one-occupant room. The mean indoor PM2.5 concentration among all sample rooms decreased from 53.2 mu g/ m(3) to 36.8 mu g/m(3) under strategy I (using air purifiers every day) and to 45.8 mu g/m(3) under strategy II (only using when outdoor PM2.5 concentration larger 75 mu g/m(3)). Under the condition of keeping the nighttime CO2 concentration below 1000 ppm, the fraction of healthy days increased from 33.1% to 59.4% and 46.9% for one- and two-occupant rooms under strategy I, respectively. The fraction of unhealthy days decreased from 18.2% to about 7% and 11% under strategy I and strategy II, respectively. Additionally, the suitable clean air change rate was 3-4 h(-1) under current usage time.