Atmospheric and Biospheric Methanol Flux Measurements: Development and Application of a Novel Technique

Abstract

A novel atmospheric methanol (CH3OH) measurement technique (M&M), employing selective gas-phase catalytic conversion of CH3OH to formaldehyde (HCHO) followed by detection of the HCHO product, is developed, tested, and applied for various studies. The effects of temperature, gas flow rate, gas composition, reactor-bed length, and reactor-bed composition on the CH3OH conversion efficiency of 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 CH3OH to HCHO conversion (>95% efficiency) achieved at a catalyst housing temperature of 345°C and an estimated sample-air/catalyst contact time of <0.2 seconds. The CH3OH and HCHO measurement accuracy was better than 6.4% at 1-75 ppb (parts per billion). Potential interferences arising from conversion of methane (CH4), carbon dioxide (CO2), ammonia (NH3), sulphur dioxide (SO2) and a suit of other VOCs (Volatile Organic Compounds) to HCHO were found to be negligible under most atmospheric conditions and catalyst housing temperatures. Applying the method, measurements of CH3OH under different atmospheric backdrops were made during various measurement campaigns and thus, are validated; whereby suggest that the new method is an inexpensive and effective way to monitor atmospheric CH3OH. Tropospheric ozone effects on plant physiological cycle and how ozone fumigated plants react against CH3OH and HCHO emissions were studied in order to identify the process based relationships arising from negative global change effects. The measured emissions of CH3OH exhibited near-exponential temperature dependence at 10°C-32°C and a strong dependence on light and stomatal conductance. During the acute ozone experiments (~170 ppb 4h-1 day-1) CH3OH and HCHO were emitted with maximum rates of about 100 µg gw-1 h-1 (micrograms per gram fresh weight per hour) and 22 µg gw-1 h-1 from plants which were 2-5 fold greater than the normal emission rates. The increase in HCHO flux and decrease in CH3OH observed during the plant recovery period clearly showed that CH3OH produced inside the plant cell was converted to HCHO as suggested by the formate cycle in plants. The increased CH3OH emission, as seen in this study, in response to higher temperatures has high correlation with climate change as the present warming climate milieu can encourage more plant growth, and therefore increased levels of VOCs in areas where VOC-emitting plants grow abundantly. So the future global climate change will have a profound impact on the emissions of these compounds and thus, will affect the chemistry of the troposphere. The in house indoor air quality measurement and assessment using M&M and PTR-MS reveals that the breathing air in our office premises is contaminated to stir disturbing problems in health and comfort of the occupant. Therefore, the study demands a serious revision of air quality standards in the working environments.