Technical Note: Determination of formaldehyde mixing ratios in air with PTR-MS: laboratory experiments and field measurements

摘要

Formaldehyde (HCHO), the most abundant carbonyl compound in the atmosphere,is generated as an intermediate product in the oxidation of nonmethanehydrocarbons. Proton transfer reaction mass spectrometry (PTR-MS) has thecapability to detect HCHO from ion signals at 31 with high time-resolution.However, the detection sensitivity is low compared to other detectablespecies, and is considerably affected by humidity, due to back reactionsbetween protonated HCHO and water vapor prior to analysis. We performed alaboratory calibration of PTR-MS for HCHO and examined the detectionsensitivity and humidity dependence at various field strengths.Subsequently, we deployed the PTR-MS instrument in a field campaign at MountTai in China in June 2006 to measure HCHO in various meteorological andphotochemical conditions; we also conducted intercomparison measurements byMulti-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS).Correction of interference in the 31 signals by fragments from protontransfer reactions with methyl hydroperoxide, methanol, and ethanol greatlyimproves agreement between the two methods, giving the correlation[HCHO]=(0.99±0.16) [HCHO]+(0.02±0.38), where error limits represent 95% confidence levels.