In conjunction with the OP3 campaign in Danum Valley, Malaysian Borneo, flux measurements of methyl chloride (CH3Cl) and methyl bromide (CH3Br) were performed from both tropical plant branches and leaf litter in June and July 2008. Live plants were mainly from the Dipterocarpaceae family whilst leaf litter samples were representative mixtures of different plant species. Environmental parameters, including photosynthetically-active radiation, total solar radiation and air temperature, were also recorded. The dominant factor determining magnitude of methyl halide fluxes from living plants was plant species, with specimens of the genus Shorea showing persistent high emissions of both gases, e.g. Shorea pilosa: 65 ± 17 ng CH3Cl h-1 g-1 (dry weight foliage) and 2.7 ± 0.6 ng CH3Br h-1 g-1 (dry weight foliage). Mean CH3Cl and CH3Br emissions across 18 species of plant were 19 (range

Background: Air pollution–mortality risk estimates are generally larger at longer-term, compared with short-term, exposure time scales.Objective: We compared associations between short-term exposure to black smoke (BS) and mortality with long-term exposure–mortality associations in cohort participants and with short-term exposure–mortality associations in the general population from which the cohorts were selected.Methods: We assessed short-to-medium–term exposure–mortality associations in the Renfrew–Paisley and Collaborative cohorts (using nested case–control data sets), and compared them with long-term exposure–mortality associations (using a multilevel spatiotemporal exposure model and survival analyses) and short-to-medium–term exposure–mortality associations in the general population (using time-series analyses).Results: For the Renfrew–Paisley cohort (15,331 participants), BS exposure–mortality associations were observed in nested case–control analyses that accounted for spatial variations in pollution exposure and individual-level risk factors. These cohort-based associations were consistently greater than associations estimated in time-series analyses using a single monitoring site to represent general population exposure {e.g., 1.8% [95% confidence interval (CI): 0.1, 3.4%] vs. 0.2% (95% CI: 0.0, 0.4%) increases in mortality associated with 10-μg/m3 increases in 3-day lag BS, respectively}. Exposure–mortality associations were of larger magnitude for longer exposure periods [e.g., 3.4% (95% CI: –0.7, 7.7%) and 0.9% (95% CI: 0.3, 1.5%) increases in all-cause mortality associated with 10-μg/m3 increases in 31-day BS in case–control and time-series analyses, respectively; and 10% (95% CI: 4, 17%) increase in all-cause mortality associated with a 10-μg/m3 increase in geometic mean BS for 1970–1979, in survival analysis].Conclusions: After adjusting for individual-level exposure and potential confounders, short-term exposure–mortality associations in cohort participants were of greater magnitude than in comparable general population time-series study analyses. However, short-term exposure–mortality associations were substantially lower than equivalent long-term associations, which is consistent with the possibility of larger, more persistent cumulative effects from long-term exposures.

[1] Methyl bromide (CH 3 Br) is a trace gas involved in stratospheric ozone depletion with both anthropogenic and natural sources. Estimates of natural source strengths are highly uncertain. In this study, >320 highly temporally and spatially resolved measurements of CH 3 Br emissions from a salt marsh in Scotland (56°00 0 N, 2°35 0 W) were made during one year using eight static enclosures. Net emissions showed both strong seasonal and diurnal cycles. Day-today maxima in emissions were associated with sunny days. Emissions dropped to zero when vegetation was removed. Mean measured CH 3 Br emission was 350 ng m À2 h À1 , but a few ''hot spots'' (measured maximum 4000 ng m À2 h À1 ) dominated integrated emissions. A crude scale-up of the annual mean emission yields an estimate for global CH 3 Br emission of $1 (0.5-3) Gg y À1 (range uses annual mean from lowest and highest emitting enclosures), $10% the global salt marsh emission regularly quoted in the literature.

Abstract. Fluxes of CH 3 Br and CH 3 Cl 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 CH 3 Br and 662 ± 266 ng m −2 h −1 for CH 3 Cl. 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. CH 3 Cl flux magnitudes from different measurement locations depended on the plant species enclosed whereas such dependency was not discernible for CH 3 Br fluxes. In 14 out of 18 collars with vegetation CH 3 Br and CH 3 Cl net fluxes were significantly positively correlated. The CH 3 Cl/CH 3 Br 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 CH 3 Br production by the relatively high bromine content in the salt marsh plant material. Extrapolation based solely on data from this study yields Correspondence to: M. R. Heal (m.heal@ed.ac.uk) salt marsh contributions of 0.5-3.2% and 0.05-0.33%, respectively, of currently-estimated total global production of CH 3 Br and CH 3 Cl, but actual global contributions likely lie between these values and those derived from southern California.

Abstract. The UK Acid Gases and Aerosol Monitoring Network (AGANet) was established in 1999 (12 sites, increased to 30 sites from 2006), to provide long-term national monitoring of acid gases (HNO3, SO2, HCl) and aerosol components (NO3−, SO42−, Cl−, Na+, Ca2+, Mg2+). An extension of a low-cost denuder-filter pack system (DELTA) that is used to measure NH3 and NH4+ in the UK National Ammonia Monitoring Network (NAMN) provides additional monthly speciated measurements for the AGANet. A comparison of the monthly DELTA measurement with averaged daily results from an annular denuder system showed close agreement, while the sum of HNO3 and NO3− and the sum of NH3 and NH4+ from the DELTA are also consistent with previous filter pack determination of total inorganic nitrogen and total inorganic ammonium, respectively. With the exception of SO2 and SO42−, the AGANet provides, for the first time, the UK concentration fields and seasonal cycles for each of the other measured species. The largest concentrations of HNO3, SO2, and aerosol NO3− and SO42− are found in southern and eastern England and smallest in western Scotland and Northern Ireland, whereas HCl are highest in south-eastern, south-western, and central England, that may be attributed to dual contribution from anthropogenic (coal combustion) and marine sources (reaction of sea salt with acid gases to form HCl). Na+ and Cl− are spatially correlated, with largest concentrations at coastal sites, reflecting a contribution from sea salt. Temporally, peak concentrations in HNO3 occurred in late winter and early spring attributed to photochemical processes. NO3− and SO42− have a spring maxima that coincides with the peak in concentrations of NH3 and NH4+, and are therefore likely attributable to formation of NH4NO3 and (NH4)2SO4 from reaction with higher concentrations of NH3 in spring. By contrast, peak concentrations of SO2, Na+, and Cl− during winter are consistent with combustion sources for SO2 and marine sources in winter for sea salt aerosol. Key pollutant events were captured by the AGANet. In 2003, a spring episode with elevated concentrations of HNO3 and NO3− was driven by meteorology and transboundary transport of NH4NO3 from Europe. A second, but smaller episode occurred in September 2014, with elevated concentrations of SO2, HNO3, SO42−, NO3−, and NH4+ that was shown to be from the Icelandic Holuhraun volcanic eruptions. Since 1999, AGANet has shown substantial decrease in SO2 concentrations relative to HNO3 and NH3, consistent with estimated decline in UK emissions. At the same time, large reductions and changes in the aerosol components provide evidence of a shift in the particulate phase from (NH4)2SO4 to NH4NO3. The potential for NH4NO3 to release NH3 and HNO3 in warm weather, together with the surfeit of NH3 also means that a larger fraction of the reduced and oxidized N is remaining in the gas phase as NH3 and HNO3 as indicated by the increasing trend in ratios of NH3 : NH4+ and HNO3 : NO3− over the 16-year period. Due to different removal rates of the component species by wet and dry deposition, this change is expected to affect spatial patterns of pollutant deposition with consequences for sensitive habitats with exceedance of critical loads of acidity and eutrophication. The changes are also relevant for human health effects assessment, particularly in urban areas as NH4NO3 constitutes a significant fraction of fine particulate matter ( < 2.5 µm) that are linked to increased mortality from respiratory and cardiopulmonary diseases.

Absolute rate constants for the removal of CH2 (5'A,) by Ar, NO, H2, and CH2CO have been measured over the temperature range 295-859 K by the method of long-path kinetic absorption spectroscopy. For quenching to the ground X^s tate by Ar, the rate constant rises by a factor of 3 over this range from its room-temperature value. Both the absolute values and their increase up to ~500 K can be explained by a mixed-state model of quenching, in which fractional populations of singlet states perturbed by nearby triplet levels and the relaxation of the corresponding triplet levels contribute to the measured removal rate. Above 500 K, there is a significant deviation between experiment and calculation, suggesting that additional high-energy perturbed singlet levels are affecting the decay process. In contrast, removal by H2 and NO, both considered to be predominantly by reaction, shows no temperature variation over this range, while removal by ketene shows a negative temperature dependence. The implications of the results to singlet methylene quenching and reaction processes at combustion temperatures are discussed.

The concentrations and input/output fluxes of trichloroacetic acid (TCA) were measured in all relevant media for one year at a 0.86 km2 upland conifer plantation and moorland catchment in SW Scotland (n > 380 separate samples analyzed). Annual wet precipitation to the catchment was 2.5 and 0.4 m for rain and cloud, respectively. TCA input to the catchment for the year was 2100 g, predominantly in rainwater (86%), with additional input via cloudwater (13%) and gas plus particle dry deposition (1%). There were no seasonal trends in TCA deposition, and cloudwater concentration was not enhanced over rainwater. TCA in precipitation exceeded concentrations estimated using currently accepted routes of gas-phase oxidation from anthropogenic chlorinated hydrocarbon precursors, in agreement with previous studies. Export of TCA from the catchment in streamwater totalled 1970 g for the year of study. The TCA concentration in streamwater at outflow (median 1.2 microg L(-1)) was significantly greater than that before the stream had passed through the conifer plantation. To well-within measurement uncertainties, the catchment is currently at steady-state with respect to TCA input/output. The catchment reservoir of TCA was dominated by soils (approximately 90%), with the remainder distributed in forest litter (approximately 9%), forest branchwood and stemwood (approximately 0.7%), forest foliage (approximately 0.5%), and moorland foliage (approximately 0.1%). Although TCA is clearly taken up into foliage, which consequently may be important for the vegetation, this was a relatively minor process for TCA at the catchment scale. If it is assumed, on the basis of laboratory extraction experiments, that only approximately 20% of "whole soil" TCA measured in this work was water extractable, then total mass of TCA in the catchment is reduced from approximately 13 to approximately 3.5 kg. Comparing the latter value with the annual flux yields an average steady-state residence time for TCA in the catchment of approximately 1-2 y, if all TCA is involved in catchment turnover. Considering that other evidence indicates the lifetime of TCA in soil and biota is considerably shorter than this (weeks rather than years), the magnitude of the TCA reservoir is suggested to be strong evidence for net natural TCA production in soils and/or that the majority of TCA in the reservoir is not involved with external fluxes.

The environmental importance of methyl bromide (CH 3 Br) arises from its contribution to stratospheric ozone loss processes and, as a consequence, its emissions from anthropogenic sources are subject to the Montreal Protocol. A better understanding of the natural budget of CH 3 Br is required for assessing the benefit of anthropogenic emission reductions and for understanding any potential effects of environmental change on global CH 3 Br concentrations. Measurements of CH 3 Br flux in temperate woodland ecosystems, in particular, are very sparse, yet these cover a large fraction of terrestrial land surface. Results presented here from 18 months of field measurements of CH 3 Br fluxes in four static flux chambers in a woodland in Scotland and from enclosures of rotting wood and deciduous and coniferous leaf litter suggest net emissions from temperate woodlands. Net CH 3 Br fluxes in the woodland varied between the chambers, fluctuating between net uptake and net emissions (À73 to 279 ng m À2 h À1 across 161 individual measurements), and with no strong seasonality, but with time-averaged net emission overall [27 AE 57 (1 SD)] ng m À2 h À1 ]. This work demonstrates that scale-up needs to be based on sufficient individual measurements to provide a reasonably constrained estimate of the long-term mean. Mean ( AE 1 SD) net CH 3 Br emissions from deciduous and coniferous leaf litter were 43 ( AE 33) ng kg À1 (dry weight) h À1 and 80 ( AE 37) ng kg À1 (dry weight) h À1 , respectively, and $ 1-2 ng kg À1 (fresh weight) h À1 from rotting woody litter. Despite the intrinsic variability, data obtained here consistently point to the conclusion that the temperate forest soil/litter ecosystem is a net source of CH 3 Br to the atmosphere.