Carl Boardman

Contrasting wetland CH4 emission responses to simulated glacial atmospheric CO2 in temperate bogs and fens.

Wetlands were the largest source of atmospheric methane (CH(4) ) during the Last Glacial Maximum (LGM), but the sensitivity of this source to exceptionally low atmospheric CO(2) concentration ([CO(2) ]) at the time has not been examined experimentally. We tested the hypothesis that LGM atmospheric [CO(2) ] reduced CH(4) emissions as a consequence of decreased photosynthate allocation to the rhizosphere. We exposed minerotrophic fen and ombrotrophic bog peatland mesocosms to simulated LGM (c. 200 ppm) or ambient (c. 400 ppm) [CO(2) ] over 21 months (n = 8 per treatment) and measured gaseous CH(4) flux, pore water dissolved CH(4) and volatile fatty acid (VFA; an indicator of plant carbon supply to the rhizosphere) concentrations. Cumulative CH(4) flux from fen mesocosms was suppressed by 29% (P < 0.05) and rhizosphere pore water [CH(4) ] by c. 50% (P < 0.01) in the LGM [CO(2) ], variables that remained unaffected in bog mesocosms. VFA analysis indicated that changes in plant root exudates were not the driving mechanism behind these results. Our data suggest that the LGM [CO(2) ] suppression of wetland CH(4) emissions is contingent on trophic status. The heterogeneous response may be attributable to differences in species assemblage that influence the dominant CH(4) production pathway, rhizosphere supplemented photosynthesis and CH(4) oxidation.

Aerosol Evolution from a Busy Road in North-West England

Motor vehicle emissions are the most significant source of particulate matter (PM) in urban environments. This study was undertaken to observe the evolution of aerosols downwind from a busy road, concentrating specifically on the aerosol total number maximum and number size distribution. A Grimm Aerosol Technik (5.400) CPC and DMA 5.5-900 classifier were used to measure ultra-fine particles from 9.8 nm to 1.1 μm at varying distances up to 100 m from the road side. Contrary to current accepted aerosol theory particle number concentration was seen to rise with increasing horizontal distance from the road side up to a maximum distance of about 100 m. As this occurred the number of fine particles was seen to increase as numbers of larger particles declined. These findings are discussed in light of existing aerosol literature on aerosol formation and dispersion.