Amid the contaminant issues, air pollution has awakened more interest due to its potential health risk and its direct effect on human productivity. The overall indoor environment quality depends on the contribution of both the indoor and the outdoor air quality. The outdoor air pollutants penetrate indoor environments through mechanical and natural ventilation as well as by infiltrations through cracks and leaks in building’s envelope. The interaction between the indoor and outdoor air may be studied by the air exchange rate. One of the most useful techniques to measure the air exchange rate is the tracer gas technique namely the metabolic CO2 decay tracer gas technique. In this technique, the outdoor CO2 concentration is usually considered constant, while in reality it follows a daily cycle. The possibility of modelling this daily cycle is fundamental to reduce the uncertainty in the calculation of air exchange rate and for a better understanding of the indoor/outdoor relationships. A better model of the outdoor air pollution, its sources and diffusion will have positive repercussion on indoor air quality modelling.
This study aims to determine the changes in ambient CO2 concentration throughout the day depending on the weather conditions in a building situated in Horst, The Netherlands. In line with this purpose, the CO2 concentration was measured inside and outside an office building in an urban location during a 2-year period. Meteorological observations and outdoor CO2 concentration were obtained from a weather station set in the building roof and atmospheric stability parameters were consulted in NOAA database. The variations and correlations of the outdoor CO2 concentration against various outdoor meteorological factors, namely temperature, dew point, relative humidity, barometric pressure, wind speed and direction, precipitation and solar irradiation were studied. It is found through statistical regression techniques that ambient CO2 concentration is negatively correlated with temperature, wind speed, wind speed gust and radiation. The correlation of the relative humidity, dew point and precipitation with the ambient CO2 concentration is not so clear because the moisture content in the air is related to the air temperature and has different effects in the vegetation. It was confirmed a relationship where ambient CO2 concentration decreases with the planetary boundary depth, the vertical mixing coefficient, downward shortwave radiation and Pasquill stability index. All these parameters increase the turbulence augmenting the diffusion of CO2 in the atmosphere. On the other hand, the pressure has local and regional effects on the winds regime. It can change local winds and therefore the local shear stress and the turbulence. On the other hand, it can also modify regional winds that can advect air masses with different properties that change the ambient CO2 concentration.