Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 5 10 2005 10.5194/acp-5-2787-2005 http://www.atmos-chem-phys.net/5/2787/2005/ http://www.atmos-chem-phys.net/5/2787/2005/acp-5-2787-2005.html http://www.atmos-chem-phys.net/5/2787/2005/acp-5-2787-2005.pdf 2787 2796 2005-10-24 Atmospheric methanol measurement using selective catalytic methanol to formaldehyde conversion S. J. Solomon T. Custer G. Schade A. P. Soares Dias J. Burrows Institute of Environmental Physics, University of Bremen, Bremen, Germany GRECAT-Grupo de Estudos de Catalise Heterogenea, Universidade Tecnica de Lisboa, Lisbon, Portugal presently with: Department of Atmospheric Sciences, Texas A&M University, Texas, USA A novel atmospheric methanol measurement technique, employing selective gas-phase catalytic conversion of methanol to formaldehyde followed by detection of the formaldehyde product, has been developed and tested. The effects of temperature, gas flow rate, gas composition, reactor-bed length, and reactor-bed composition on the methanol conversion efficiency of a molybdenum-rich, iron-molybdate catalyst [Mo-Fe-O] were studied. Best results were achieved using a 1:4 mixture (w/w) of the catalyst in quartz sand. Optimal methanol to formaldehyde conversion (>95% efficiency) occurred at a catalyst housing temperature of 345°C and an estimated sample-air/catalyst contact time of <0.2 seconds. Potential interferences arising from conversion of methane and a number of common volatile organic compounds (VOC) to formaldehyde were found to be negligible under most atmospheric conditions and catalyst housing temperatures. Using the new technique, atmospheric measurements of methanol were made at the University of Bremen campus from 1 to 15 July 2004. Methanol mixing ratios ranged from 1 to 5 ppb with distinct maxima at night. Formaldehyde mixing ratios, obtained in conjunction with methanol by periodically bypassing the catalytic converter, ranged from 0.2 to 1.6 ppb with maxima during midday. These results suggest that selective, catalytic methanol to formaldehyde conversion, coupled with existing formaldehyde measurement instrumentation, is an inexpensive and effective means for monitoring atmospheric methanol.