A sulfur-specific flame photometer has been used for the real time measurement of sulfur-containing aerosols. Specificity for the aerosols was achieved with a diffusion tube stripper which removed sulfur-containing gases from the air stream by diffusion to an adsorbing wall but transmitted particles to the flame photometer. The sensitivity of the flame photometer to (NH4)2SO4 and NH4HSO4 aerosols was identical, but a reduced response was found for H2SO4 aerosol. This occurred because of the high temperature (145°C) of the flame photometer burner block which caused the evaporation and loss of H2SO4 to the wall before reaching the flame. The addition of NH3 to the sample air just upstream of the burner converted H2SO4 to (NH4)2SO4 or NH4HSO4 and produced the expected increase in the flame photometer response. Heating the aerosol upstream of the diffusion stripper converted the sulfates to sulfur-containing gases over a temperature range characteristic of the aerosol being sampled. These gases were removed in the stripper, thereby decreasing the flame photometer output. The normalized response to aqueous H2SO4 aerosol decreased from unity at 50°C to 0.04 at 110°C and for (NH4)2SO4 and NH4HSO4 aerosols from unity at 115°C to zero at 190°C. When the aerosol contained both H2SO4 and (NH4)2SO4, the resultant thermogram was a function of both the (NH4)2SO4/H2SO4 ratio and the manner in which the two components were mixed in the particles comprising the aerosol (i.e. homogeneously with constant (NH4)2SO4/H2SO4 ratios or heterogeneously with varying ratios).
ASJC Scopus subject areas
- General Environmental Science
- General Earth and Planetary Sciences