Indoor-outdoor relationship of PM2.5 mass concentrations in severe cold regions based on a coupled canopy model

In the recent years, air pollution has become increasingly serious. Residential areas are the places where urban residents spend most their time. Air quality in residential areas and indoor environments significantly affects human health. The particle pollution characteristics of the cities in severely cold regions are spectacular due to unique climate characteristics of these cities, their urban energy consumption structures, underlying surfaces and architectural shape. All these characteristics significantly differ from those of other cities, and this difference is the main driver of unique particle pollution characteristics. This study established an indoor-outdoor particle diffusion model for cities in severely cold regions and it can be used to evaluate the relationship between indoor and outdoor particle concentrations. First, we found that there is a time lag of about 2 h for indoor PM2.5 mass concentrations relative to outdoors in conditions of the infiltration in the residential home.As for the relationship between indoor and outdoor PM2.5, the simulation results showed that the I/O ratios were greater for higher floors of buildings because of the differences in outdoor meteorological conditions in the vertical direction. In addition, indoor source emissions and large openings could significantly influence indoor particle concentration levels.