http://hdl.handle.net/1842/3012 2013-05-24T11:57:46Z http://hdl.handle.net/1842/4839 Title: Methyl bromide and methyl chloride fluxes from temperate forest litter Authors: Blei, Emanuel; Heal, Mathew R Abstract: Methyl halide fluxes were measured from fine (nonwoody) litter samples in a temperate deciduous forest site in Scotland on 16 occasions over more than a year and from a coniferous forest site. The resulting mean (+/-1 sd) CH3Br and CH3Cl fluxes were 4.1 +/- 3.7 ng kg-1 h-1 and 0.98 +/- 0.62 µg kg-1 h-1, respectively, for dry mass leaf litter and 5.7 +/- 6.3 ng kg-1 h-1 and 0.47 +/- 0.14 µg kg-1 h-1 for dry mass needle litter. Temporal variations of net fluxes from leaf litter were significantly greater than spatial variations suggesting seasonality in the fluxes. The mean CH3Cl/CH3Br mass ratio of fluxes was ~200, an order of magnitude larger than the ratio of their estimated global turnovers. Temperate forest litter may be a moderate net source of CH3Cl globally but a negligible source of CH3Br. These statements refer to the nonwoody litter component only. 2011-03-01T00:00:00Z http://hdl.handle.net/1842/4404 Title: Large estragole fluxes from oil palms in Borneo Authors: Misztal, Pawel K; Owen, Susan M; Guenther, Alex B; Rasmussen, R; Geron, C; Harley, P; Phillips, Gavin J; Ryan, A; Edwards, D P; Hewitt, C N; Nemitz, Eiko; Siong, J; Heal, Mathew R; Cape, J Neil Abstract: During two field campaigns (OP3 and ACES), which ran in Borneo in 2008, we measured large emissions of estragole (methyl chavicol; IUPAC systematic name 1-allyl-4-methoxybenzene; CAS number 140-67-0) in ambient air above oil palm canopies (0.81 mg m−2 h−1 and 3.2 ppbv for mean midday fluxes and mixing ratios respectively) and subsequently from flower enclosures. However, we did not detect this compound at a nearby rainforest. Estragole is a known attractant of the African oil palm weevil (Elaeidobius kamerunicus), which pollinates oil palms (Elaeis guineensis). There has been recent interest in the biogenic emissions of estragole but it is normally not included in atmospheric models of biogenic emissions and atmospheric chemistry despite its relatively high potential for secondary organic aerosol formation from photooxidation and high reactivity with OH radical. We report the first direct canopy-scale measurements of estragole fluxes from tropical oil palms by the virtual disjunct eddy covariance technique and compare them with previously reported data for estragole emissions from Ponderosa pine. Flowers, rather than leaves, appear to be the main source of estragole from oil palms; we derive a global estimate of estragole emissions from oil palm plantations of ~0.5 Tg y−1. The observed ecosystem mean fluxes (0.44 mg m−2 h−1) and mean ambient volume mixing ratios (3.0 ppbv) of estragole are the highest reported so far. The value for midday mixing ratios is not much different from the total average as, unlike other VOCs (e.g. isoprene), the main peak occurred in the evening rather than in the middle of the day. Despite this, we show that the estragole flux can be parameterised using a modified G06 algorithm for emission. However, the model underestimates the afternoon peak even though a similar approach works well for isoprene. Our measurements suggest that this biogenic compound may have an impact on regional atmospheric chemistry that previously has not been accounted for in models and could become more important in the future due to expansion of the areas of oil palm plantation. 2010-01-01T00:00:00Z http://hdl.handle.net/1842/4403 Title: Modelling surface ozone during the 2003 heat-wave in the UK Authors: Vieno, Massimo; Dore, A J; Stevenson, David S; Doherty, Ruth; Heal, Mathew R; Reis, Stefan; Hallsworth, Stephen; Tarrason, L; Wind, P; Fowler, David; Simpson, David; Sutton, Mark A Abstract: The EMEP4UK modelling system is a high resolution (5×5 km2) application of the EMEP chemistry-transport model, designed for scientific and policy studies in the UK. We demonstrate the use and performance of the EMEP4UK system through the study of ground-level ozone (O3) during the extreme August 2003 heat-wave. Meteorology is generated by the Weather Research and Forecast (WRF) model, nudged every six hours with reanalysis data. We focus on SE England, where hourly average O3 reached up to 140 ppb during the heat-wave. EMEP4UK accurately reproduces elevated O3 and much of its day-to-day variability during the heat-wave. Key O3 precursors, nitrogen dioxide and isoprene, are less well simulated, but show generally accurate diurnal cycles and concentrations to within a factor of ~2–3 of observations. The modelled surface O3 distribution has an intricate spatio-temporal structure, governed by a combination of meteorology, emissions and photochemistry. A series of sensitivity runs with the model are used to explore the factors that influenced O3 levels during the heat-wave. Various factors appear to be important on different days and at different sites. Ozone imported from outside the model domain, especially the south, is very important on several days during the heat-wave, contributing up to 85 ppb. The effect of dry deposition is also important on several days. Modelled isoprene concentrations are generally best simulated if isoprene emissions are changed from the base emissions: typically doubled, but elevated by up to a factor of five on one hot day. We found that accurate modelling of the exact positions of nitrogen oxide and volatile organic compound plumes is crucial for the successful simulation of O3 at a particular time and location. Variations in temperature of ±5 K were found to have impacts on O3 of typically less than ±10 ppb. 2010-01-01T00:00:00Z http://hdl.handle.net/1842/4402 Title: Long-term CH3Br and CH3Cl flux measurements in temperate salt marshes Authors: Blei, Emanuel; Heal, Mathew R; Heal, Kate V Abstract: Fluxes of CH3Br and CH3Cl and their relationship with potential drivers such as sunlight, temperature and soil moisture, were monitored at fortnightly to monthly intervals for more than two years at two contrasting temperate salt marsh sites in Scotland. Manipulation experiments were conducted to further investigate possible links between drivers and fluxes. Fluxes followed both seasonal and diurnal trends with highest fluxes during summer days and lowest (negative) fluxes during winter nights. Mean (± 1 sd) annually and diurnally-weighted net emissions from the two sites were found to be 300 ± 44 ng m−2 h−1 for CH3Br and 662 ± 266 ng m−2 h−1 for CH3Cl. The fluxes from this work are similar to findings from this and other research groups for salt marshes in cooler, higher latitude climates, but lower than values from salt marshes in the Mediterranean climate of southern California. Statistical analysis generally did not demonstrate a strong link between temperature or sunlight levels and methyl halide fluxes, although it is likely that temperatures have a weak direct influence on emissions, and both certainly have indirect influence via the annual and daily cycles of the vegetation. CH3Cl flux magnitudes from different measurement locations depended on the plant species enclosed whereas such dependency was not discernible for CH3Br fluxes. In 14 out of 18 collars with vegetation CH3Br and CH3Cl net fluxes were significantly positively correlated. The CH3Cl/CH3Br net-emission mass ratio was 2.2, a magnitude lower than mass ratios of global methyl halide budgets (~22) or emissions from tropical rainforests (~60). This is likely due to preference for CH3Br production by the relatively high bromine content in the salt marsh plant material. Extrapolation based solely on data from this study yields salt marsh contributions of 0.5–3.2% and 0.05–0.33%, respectively, of currently-estimated total global production of CH3Br and CH3Cl, but actual global contributions likely lie between these values and those derived from southern California. 2010-11-01T00:00:00Z