The significance of indoor:outdoor relationships, and physical and chemical composition in personal exposure to urban particulate matter

Abstract

Over recent years there has been mounting evidence suggesting that airborne particulate matter may be responsible for the aggravation of a number of respiratory illnesses. Because of these health implications it is considered important to understand the sources of airborne particles, the pathways leading to human exposure and the variables affecting the degree of exposure. The main objectives of this research is to assess the relationships between indoor and outdoor respirable particulate matter, the primary factors influencing this relationship and how this may relate to personal exposure. In addition, it was also felt important to determine any relationships between different sources and sinks of particulate matter, such as street dust and dust present on indoor surfaces. Simultaneous indoor and outdoor measurements of respirable particulate matter were undertaken in three buildings located in Wolverhampton City Centre. Two of the buildings are situated in a road used by approximately 10,000 diesel buses each day, with 4 and 5 storey buildings along both sides of the road producing a small street canyon effect. Monitoring indoor and outdoor particulate concentrations inside one of these buildings for one year has shown that meteorology, building location and building use can have a significant effect upon airborne particulate concentrations both indoors and outdoors. For example, a greater wind speed caused an increase in particles penetrating indoors and particulate levels were generally lower, indoors and outdoors, when wind was flowing parallel to the canyon. Particulate concentrations were also 111 significantly greater inside the street canyon and the buildings located within the canyon when compared to another location in Wolverhampton City Centre. Chemical analysis of airborne particles and deposited dusts suggests that the majority of the particulate in the busy street canyon is likely to be diesel engine and vehicle related. The magnetic signature of the dusts collected from the street canyon also varies from dusts collected from other locations, for example the XARM/SIRM ratio is approximately half of other street dusts collected in the West Midlands. Airborne particulate, street dusts and surface dusts from several roads and buildings were chemically and morphologically analysed using a variety of methods to assess the relationships between these sources and sinks of particulate matter. This analysis suggests that dust moves freely between being airborne or deposited, enabling the formulation of a schematic model, illustrating this movement.