EFFECTS OF RELATIVE-HUMIDITY ON GAS-PARTICLE PARTITIONING OF SEMIVOLATILE ORGANIC-COMPOUNDS TO URBAN PARTICULATE MATTER

A useful, compound-dependent gas/particle partition coefficient in the atmosphere is K(p) = (F/TSP)/A where F (ng/m3) and A (ng/m3) are the particle-associated and gaseous concentrations, and TSP (mug/m3) is the total suspended particulate matter concentration. K(p) depends on temperature (T, K) according to log K(p) = m(p)/T + b(p). Using urban field data from Osaka, Japan, the effects of relative humidity (RH, %) on measured K(p) values are examined over the range 42 % less-than-or-equal-to relative humidity less-than-or-equal-to 95 %. A residual value is defined as the difference between each observed value of log (F/TSP)/A and the value calculated by using log (F/TSP)/A = m(p)/T + b(p). Statistically significant correlations of the type residual = c(p)RH + d(p) are found for seven PAHs or groups of PAHs, namely, phenanthrene + anthracene; Me-phenanthracene + Meanthracene; fluoranthene; pyrene; benzo[a+b]fluorene; chrysene + benz[a]anthracene + triphenylene; and benzo[b]fluoranthene + benzo[a]fluoranthene. The overall correlation is then log (F/TSP)/A = m(p)/T + b(p) + c(p)RH + d(p). In all seven cases, the values of c(p) were found to be negative, indicating a decrease in log (F/TSP)/A with increasing relative humidity. For fluoranthene, c(p) = -0.00528 and d(p) = 0.381.