The health effects of particle inhalation including urban air pollution and tobacco smoke comprise a significant public health concern worldwide, although the mechanisms by which inhaled particles cause premature deaths remain undetermined. In this study, we assessed the physicochemical interactions of fine airborne particles (PM(2.5)) and lung lining liquid using scanning electron microscopy, atomic force microscopy, and X-ray photon spectroscopy. We provide experimental evidence to show that lung lining liquid modifies the chemistry and attractive forces at the surface of PM(2.5), which leads to enhanced particle aggregation. We propose that this is an important protective mechanism that aids particle clearance in the lung.

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Numerous epidemiological studies have found associations between ambient particulate matter and adverse health outcomes. The importance of indoor particles has also been recognised since people spend an average of 90% of their time indoors. In order to better understand exposure to particles this study was carried out to provide data on the characteristics of airborne particulate matter found inside homes in the UK. Forty -eight -h measurements were taken at 10 houses during the summer of 1999. Particulate matter with a 50% cut -off efficiency at an aerodynamic diameter of 2.5 m (PM 2.5 ) and total suspended particulate ( TSP ) mass concentrations were measured gravimetrically in the kitchen and living room of each home. Concurrent continuous measurements of particle number concentrations over eight different aerodynamic diameter size ranges were made with an optical particle counter. Occupants were asked to complete a time ± activity diary and a short questionnaire relating to various housing characteristics for the 48 -h period. The volunteers spent approximately 60% of their time at home indoors. The geometric mean concentration of TSP over the 48 h was 32 g / m 3 in the kitchen and 41 g / m 3 in the living room. The geometric mean concentration of PM 2.5 was 13 g / m 3 in the kitchen ( integrated over the entire 48 -h period ) and 12 g / m 3 in the living room ( integrated over the time the volunteer was present in the house ) with a range of 5 to 77 g / m 3 . The continuous measurements showed large variability over the day as a result of activities such as cooking and smoking and the patterns were similar in the kitchen and the living room. A good correlation of both mass and mean number concentration between rooms indicated a high degree of spatial uniformity.