Particle size distributions, PM2.5 concentrations and water-soluble inorganic ions in different public indoor environments: a case study in Jinan, China

In this study, we collected particles with aerodynamic diameter ?2.5 μm (PM_2.5) from three different public indoor places (a supermarket, a commercial office, and a university dining hall) in Jinan, a medium-sized city located in northern China. Water-soluble inorganic ions of PM_2.5 and particle size distributions were also measured. Both indoor and outdoor PM_2.5 levels (102.3–143.8 μg·m^?3 and 160.2–301.3 μg·m^?3, respectively) were substantially higher than the value recommended by the World Health Organization (25 μg·m^?3), and outdoor sources were found to be the major contributors to indoor pollutants. Diurnal particle number size distributions were different, while the maximum volume concentrations all appeared to be approximately 300 nm in the three indoor locations. Concentrations of indoor and outdoor PM_2.5 were shown to exhibit the same variation trends for the supermarket and dining hall. For the office, PM_2.5 concentrations during nighttime were observed to decrease sharply. Among others, SO ₄ ^2? , NH ₄ ⁺ and NO ₃ ^? were found to be the dominant water-soluble ions of both indoor and outdoor particles. Concentrations of NO ₃ ^? in the supermarket and office during the daytime were observed to decrease sharply, which might be attributed to the fact that the indoor temperature was much higher than the outdoor temperature. In addition, domestic activities such as cleaning, water usage, cooking, and smoking also played roles in degraded indoor air quality. However, the results obtained here might be negatively impacted by the small number of samples and short sampling durations.