Comparison of daily and working-time mean concentrations ofindoor typical pollutants in an office building in Beijing

The reasonability of using 24-hour mean pollutant concentration to evaluate the indoor air quality in the buildings with clear working schedules, as presented by office buildings, is not clear. Based on one-month real-time monitoring data of indoor CO2and PM2.5 concentrations in an office building located in Beijing, this paper investigates the correlation between the daily (24-hour) mean concentration and the working-time (07：00-19：00) mean concentration. The results show that the exceeding rates of indoor CO2and PM2.5 daily mean concentrations are less than 2% against the GB/T 18883-2022, but the exceeding rate of the working-time mean concentration is 1.25 to 20 times higher than that of the daily mean concentration. There is a large deviation between the daily mean value and the working-time mean value. The maximum value of PM2.5 relative deviation is 0.45, and the median value is 0.14. The maximum value of CO2relative deviation is 0.34, and the median value is 0.04. Compared to the Chinese standard, the probability of missed judgment of indoor CO2is 100%, while the probability of wrong penalty is 0. Similarly, the probability of missed judgment and wrong penalty of indoor PM2.5 is 62.3% and 19.7%, respectively. Moreover, the probabilities of wrong penalty and missed judgment are closely related to the evaluation standard, and decrease when the stricter standard with the smaller limit is applied. Thus, for the air quality evaluation of real office buildings, specific attention should be paid to the working-time mean pollutant concentration, and the appropriate evaluation standards as well as suitable concentration limits should be selected. The results provide a new perspective to accurately and effectively evaluate the air quality of office buildings.