Atmospheric methanol measurement using selective catalytic methanol to formaldehyde conversion

Abstract

Abstract.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, ironmolybdate 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.

First space-based derivation of the global atmospheric methanol emission fluxes

“…These emission factors are based on whole ecosystem net methanol flux measurements reported by 17 studies that characterized various ecosystems including tropical forest (Geron et al, 2002;Karl et al, 2004Karl et al, , 2007Langford et al, 2010), warm conifer forest (Karl et al, 2005), cool temperate conifer forest (Schade and Goldstein, 2001;Baker et al, 2001;Karl et al, 2002), temperate broadleaf forest and plantation (Spirig et al, 2005;Karl et al, 2003a;Jardine et al, 2008), boreal forest (Rinne et al, 2007), croplands (Warneke et al, 2002;Schade and Custer, 2004) and grassland (Kirstine et al, 1998;Fukui and Doskey, 1998;Ruuskanen et al, 2010). Among these studies, Kirstine et al (1998) and Fukui and Doskey (1998) have used whole ecosystem enclosure techniques with gas chromatography analysis to quantify emissions from grasslands, Schade and Goldstein (2001), Baker et al (2001) and Geron et al (2002) used above canopy relaxed eddy accumulation with gas chromatography analysis to measure methanol fluxes above forests, whereas all the other studies used protontransfer reaction mass spectroscopy (PTR-MS) and the eddy covariance, or disjunct eddy covariance, approach (see Karl et al, 2002).…”

“…Long-term BVOC ecosystem-scale flux measurements were performed from a 52 m high tower by the disjunct eddycovariance technique (see e.g. Spirig et al, 2005) (Senten et al, 2008;Vigouroux et al, 2009). For this work we focus on the period between June and December 2009.…”

“…Galbally and Kirstine, 2002;Jacob et al, 2005;Millet et al, 2008); (iii) field and aircraft measurements (e.g. Singh et al, 2000;Karl et al, 2003a;Millet et al, 2004;Spirig et al, 2005;Mao et al, 2006).…”

Technical Note: Intercomparison of formaldehyde measurements at the atmosphere simulation chamber SAPHIR

“…The aqueous HCHO then reacts with NH + 4 and acetyl acetone (Hantzsch reaction) inside the liquid reactor forming a fluorescent product, 3,5-diacetyl-1,4-dihydrolutidine (DDL), which is continuously monitored. For the experiments presented here a two-way inlet system was used to allow semi-continuous measurements of HCHO and methanol (Solomon et al, 2005). Air was sampled at a constant flow rate of 1.7 l min −1 (STP) from the glass manifold via a Teflon PFA tube (OD=6.35 mm), passed through a Teflon pump (KNF Neuberger Inc., Model N86 KTDC B, Trenton, New Jersey, USA) and directed into a 3-way PFA Teflon valve (Metron Technologies, Unterschleissheim, Germany) where it was either diverted through a catalytic methanol-to-formaldehyde converter for methanol measurements or directly led to the instrument for HCHO measurements (Solomon et al, 2005).…”

“…For the experiments presented here a two-way inlet system was used to allow semi-continuous measurements of HCHO and methanol (Solomon et al, 2005). Air was sampled at a constant flow rate of 1.7 l min −1 (STP) from the glass manifold via a Teflon PFA tube (OD=6.35 mm), passed through a Teflon pump (KNF Neuberger Inc., Model N86 KTDC B, Trenton, New Jersey, USA) and directed into a 3-way PFA Teflon valve (Metron Technologies, Unterschleissheim, Germany) where it was either diverted through a catalytic methanol-to-formaldehyde converter for methanol measurements or directly led to the instrument for HCHO measurements (Solomon et al, 2005). Gas phase HCHO calibration was performed using a permeation tube-based gas standard generator (KIN-TEK, Model 491 MB, LaMarque, Texas, USA) providing an accuracy of 8%.…”