Correlation Between Outdoor And Indoor Air Pollutants

People generally spend most of their time indoors. Indoor air quality (IAQ) is directly related to human health and working efficiency. Usually, there is interaction and interrelation between indoor and outdoor environmental parameters. Therefore, the quantitative relation between them is worthy of being studied, especially correlation between outdoor and indoor air pollutants.The theoretical analysis and site measurement are together combined in this research. After discussing the relationship between some dominant factors affecting IAQ, several pollutants (HCHO,CO,CO₂ and particulate matter, PM), which closely relate to human health in indoor and outdoor environments of buildings, and waste heat rejected by air conditioning were investigated. First, based the principle of system engineering, the interpretative structural modeling (ISM) that related to the relationship among the factors affecting indoor air quality (IAQ) in buildings is established, which indicates that there are five layers among these factors.Second, the particulate matter concentrations in an office and residential room were measured. Then indoor and outdoor particle concentrations and their ratios (I/O) were analysed. For buildings that without any indoor sources and with low human activity, the indoor particulate matters mainly come from the outdoor particulate matters. So for the buildings near roadside without industrial pollution sources, the indoor particulate matter in fact primarily comes from the traffic emissions. Both the concentration of indoor and outdoor particulates of the apartment room and office room vary with time, and tendency of their variation is similar. The I/O ratio increases as the size of particles decreases, which indicates that the fine particles penetrate through the building envelopes more easily. The concentration of indoor particles is closely correlated with that of outdoor particles, and the correlation increases as particle size reduces. The concentration of indoor particle is correlated with environmental parameters to some extent. For the apartment, the concentration of indoor particle is positively correlated with the indoor/outdoor temperature; and it is negatively correlated with the indoor/outdoor humidity and wind speed.Through the survey of three shopping malls in Shanghai, results demonstrated that different floors at the shopping malls have different concentrations of CO₂, HCHO and PM (PM10, PM2.5, PM1). Moreover, owing to big area of shopping malls and different merchandises for sale at each floor, there was difference on concentration of CO₂, HCHO and PM (PM10, PM2.5, PM1) even at the same floor. These problems should be taken into consideration when designing an air conditioning system. In two shopping malls without indoor sources besides the consumers and where occupant density is under middle level, the indoor concentrations of PM10,PM2.5,PM1are lower than outdoor concentrations, and the I/O ratios below unity. In one shopping mall with indoor sources like cooking and where occupant density is under high level, the indoor concentrations of PM10,PM2.5,PM1 are higher than outdoor concentrations, and the I/O ratios above unity. It implies that the pollution from particulate matter in this shopping mall is much serious indoors than outdoors. In this environment, except human activity, the airborne particulate matter from cooking and combustion should be controlled in order to improve indoor air quality.The survey results of eight shopping malls in Wuhan demonstrated that different floors at the shopping malls have different concentrations of CO₂, HCHO and PM (PM10, PM2.5, and PM1). Moreover, due to big area of shopping malls and different merchandises for sale at each floor, there were differences in concentration of CO₂, HCHO and PM (PM10, PM2.5, and PM1) even at the same floor. These problems should be taken into consideration when designing an air conditioning system. Different merchandises emitted different harmful pollutants due to their different composition. During operation of air conditioning systems at the shopping malls without indoor sources besides the customers and where occupant density is under middle level, the indoor concentrations of TSP, PM10,PM2.5,PM1 are lower than outdoor concentrations. During the non-operation of air conditioning system in the floor of a shopping mall with indoor sources like cooking and where occupant density is under high level, the indoor concentrations of TSP, PM10,PM2.5,PM1 are equal to or higher than outdoor concentrations, and the indoor/outdoor (I/O) ratios equal to or above unity. It implies that the pollution from particulate matter at this situation is much more serious indoors than outdoors and the indoor source has much contribution to the concentration of indoor particulate matter. In this environment, except human activity, the airborne particulate matter from cooking and combustion should be controlled in order to improve indoor air quality.The measurement results of the inside microenvironment parameters for different types of air conditioned vehicles in Shanghai demonstrate that the inside temperature and humidity can usually meet human thermal comfort in most time, but around sunny noon the temperature inside bus is high, even far higher than human comfort zone temperature due to strong sunny radiation. There is a remarkable difference between the inside air environment parameters of different types of air-conditioned urban transit vehicles. Usually, there is good air quality inside the light rail and subway carriages. Poor air quality inside air-conditioned bus exists, which CO₂ concentration may be high to 3223ppm, CO concentration high to 18ppm sometimes, and HCHO concentration is high. Therefore, the thermal comfort and air quality inside air-conditioned bus need to be improved.Finally, the influence of air conditioners utilization on urban thermal environment is studied. The urban heat island effect is essentially a kind of thermal pollution caused by artificial activity. Air conditioning units used in buildings release a great deal of heat into outdoors while they improve the indoor thermal environment. Therefore, this will cause a rise in the outside air temperature and strengthen the urban heat island effect. The model for calculating the rise in atmospheric temperature caused by domestic air conditioners is proposed and used to determine the rise in the outside air temperature in Wuhan. The results demonstrate that the rise in atmospheric temperature is 2.56℃under inversion conditions and 0.2℃under normal conditions, which indicates that thermal pollution is serious when the atmosphere is stable. To a certain extent, the rise of atmospheric temperature can be verified by the rise of lowest atmospheric temperature of Wuhan over recent years. The study is helpful to seek for methods to improve indoor air quality and and layout of building and environment.