Long-term characteristics of formaldehyde concentrations in four Chinese residences and estimation of annual average

Long-term characteristics of concentrations of indoor formaldehyde is critical to evaluate health risk and burden of disease and better protect occupants’ health. However, long-term measurement of pollutants with a high time coverage degree (TCD, defined as sampling duration/sampling period) remains a challenge. To address this issue, we measured week-average formaldehyde concentrations by continuously weekly sampling utilizing a low flow-rate active sampler. This achieved a TCD of 100 %, which is significantly higher than those previously reported (0.05 %-0.7 %). Concentration profiles obtained in four Chinese residences for about one-year show that the highest concentration occurs in summer, followed by spring and autumn, and the lowest in winter. The ratios of summer to winter concentration varied from 1.4 to 3.5, which was linearly correlated with annual average concentration (Pearson correlation coefficient=0.81). Although compliance with standard threshold (0.08 mg/m³) in winter, severe exceedance (38 % to 77 %) was found in three residences in summer. This highlights necessity of worst-scenario prediction in attainment evaluation, instead of single-point test. A Monte Carlo analysis revealed that deviation of estimated annual average concentration decreased as TCD of a sampling strategy increased. Sampling for one week once a season had an estimation deviation less than 30 % in average. This work provides new insights to realize long-term assessment of exposure to indoor pollutants.