Indoor-to-outdoor relationship of aerosol particles inside a naturally ventilated apartment – A comparison between single-parameter analysis and indoor aerosol model simulation

Abstract

The indoor-to-outdoor relationship of aerosol particles is affected by several mechanisms including penetration, ventilation rate, dry deposition rate and sources. Understanding the effect of these factors is essential for a deeper knowledge of the indoor-to-outdoor relationship. In real-life conditions, it is difficult to analyze these factors in a naturally ventilated environment. In this study, a naturally ventilated and an occupied apartment was used to investigate the indoor-to-outdoor relationship of aerosol particles by applying two different techniques; single-parameter analysis and indoor aerosol model simulation. The indoor aerosol model simulation approach can describe the effect of these factors based on high time-resolution calculations and it is a powerful and robust approach. Single parameter analysis is very simple to apply but it is valid under certain conditions. In the absence of indoor activities (i.e. nighttime) and based on the particle number concentrations, the I/O ratio was <1 during spring but ~1.2 during winter. Based on the indoor aerosol model simulation results for the coarse fraction, the penetration factor (P) was 0.3–1, the ventilation rate (λ) was 0.1–2h−1, and the deposition rate (λd) was ~0.15h−1. The coarse particles concentration was strongly affected by indoor activities. During extreme mechanical activities (e.g. vacuum cleaning), the concentration increased by a factor of 9 (source strength ~160particles/h). During children play, the coarse fraction concentration increased by a factor of 3 (source strength ~10particles/h). Spraying an insect pesticide increased the coarse fraction concentration by a factor of 9 (source strength ~420particles/h). Water-pipe tobacco smoking produced huge amounts of both micron and submicron particulate matter; it caused the coarse fraction concentration to significantly increase by a factor of 18 (source strength ~140particles/h). The use of natural gas heater affected the submicron fraction only and did not affect the micron fraction.