Detection of sulfur dioxide and sulfuric acid at high relative humidity was studied using a chemical ionization mass spectrometer (CIMS). The reactant ions used in the experiments are CO3-·nH 2O (n=0-5), which react with SO2 to form SO 5-·nH2O (n=0-2). H2SO 4 reacts with the precursor ions to form HSO4- (m/z=97amu) and H2SO4·CO3- (m/z=158amu). We report the first use of the latter ionization scheme to detect sulfuric acid. High RH affects the detection of SO2 and H 2SO4 by forming clusters with the reactant and product ions, reducing sensitivity. Increasing the temperature breaks these clusters. For SO2 at high RH, either SO5- (m/z=112amu) or SO5-·H2O (m/z=130amu) can be used for SO2 detection without a decrease in sensitivity. For H 2SO4 at high RH, it is preferred to detect the ion H 2SO4·CO3- because the background signal at 158amu is small, and a better sensitivity can be achieved.
- Chemical ionization mass spectrometer
- Relative humidity
- Sulfur dioxide
- Sulfuric acid
- Water clusters