THE ATMOSPHERIC PARTITIONING OF DECAMETHYLCYCLOPENTASILOXANE (D5) AND1-HYDROXYNONAMETHYLCYCLOPENTASILOXANE (D4TOH) ON DIFFERENT TYPES OF ATMOSPHERIC PARTICLES

A series of outdoor chamber experiments using different types of atmos pheric particles were conducted to investigate the atmospheric gas-par ticle partitioning behavior of decamethylcyclopentasiloxane (D5) and i ts hydroxylated compound, 1-hydroxynonamethylcyclopentasiloxane (D4TOH ). This was undertaken because the phase in which a compound exists di rectly influences its lifetime in the atmosphere, its deposition to th e surface of the earth, and ultimately its potential impacts on human health. To measure the phase distribution, or partitioning, between th e gas and particle phases, aerosol systems were created in either the 190 m(3) or 25 m(3) outdoor Tenon film chambers at the UNC chamber fac ility in Pittsboro, NC. Diesel wood, and coal soot were used as organi c combustion particle sources, while Arizona fine dust was used as an inorganic particle source. The gas-particle partition coefficient, K-p , was used as a measure of the phase distribution. K-p can be expresse d as K-p = (C-p/TSP)/C-g, where C-p(ng/m(3)) and C-g(ng/m(3)) are the concentrations in the particle and gas phases respectively, and TSP (m u g/m(3)) is the total suspended particulate matter concentration. The effect of temperature is considered to be the key parameter that affe cts the partitioning coefficient. Chamber data showed for both D5 and D4TOH partitioning, that temperature was very important and could infl uence partitioning to the particle phase by two orders of magnitude in going from 25 to 0 degrees C. It was also found that relative humidit y (RH) was an important parameter affecting D4TOH partitioning especia lly with mineral dust particles. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.