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Flux measurements of nitrogen oxides (NOx) were made over London using airborne eddy-covariance from a low flying aircraft. Seven low altitude flights were conducted over Greater London performing multiple over-passes across the city during eight days in July 2014. NOx fluxes across the Greater London region exhibited high heterogeneity and strong diurnal variability, with central areas responsible for the highest emission rates (20 - 30 mg m-2 h-1). Other high emission areas included the M25 orbital motorway. The complexity of London's emission characteristics makes it challenging to pinpoint single emission sources definitively using airborne measurements. Multiple sources, including road transport and residential, commercial and industrial combustion sources are all likely to contribute to measured fluxes. Measured flux estimates were compared to scaled National Atmospheric Emissions Inventory (NAEI) estimates, accounting for; monthly, daily and hourly variability. Significant differences were found between the flux-driven emissions and the NAEI estimates across Greater London, with measured values up to two times higher in Central London than those predicted by the inventory. To overcome the limitations of using the national inventory to contextualise measured fluxes, we used physics-guided flux data fusion to train environmental response functions (ERF) between measured flux and environmental drivers (meteorological and surface). The aim was to generate time-of-day emission surfaces using calculated ERF relationships for the entire Greater London region (GLR). 98% spatial coverage was achieved across GLR at 400 m² spatial resolution. All flight leg projections showed substantial heterogeneity across the domain, with high emissions emanating from Central London and major road infrastructure. The diurnal emission structure of the GLR was also investigated, through ERF, with the morning rush-hour distinguished from lower emissions during the early afternoon. Overall, the integration of airborne fluxes with an ERF-driven strategy enabled the first independent generation of surface NOx emissions, at high resolution using an eddy-covariance approach, for an entire city region. [ABSTRACT FROM AUTHOR]

Direct measurements of NOx , CO and aromatic volatile organic compound (VOC) (benzene, toluene, C 2 -benzenes and C 3 -benzenes) flux were made for a central area of Beijing using the eddy-covariance technique. Measurements were made during two intensive field campaigns in central Beijing as part of the Air Pollution and Human Health (APHH) project, the first in November–December 2016 and the second during May–June 2017, to contrast wintertime and summertime emission rates. There was little difference in the magnitude of NOx flux between the two seasons (mean NOx flux was 4.41 mg m -2 h -1 in the winter compared to 3.55 mg m -2 h -1 in the summer). CO showed greater seasonal variation, with mean CO flux in the winter campaign (34.7 mg m -2 h -1) being over twice that of the summer campaign (15.2 mg m -2 h -1). Larger emissions of aromatic VOCs in summer were attributed to increased evaporation due to higher temperatures. The largest fluxes in NOx and CO generally occurred during the morning and evening rush hour periods, indicating a major traffic source with high midday emissions of CO, indicating an additional influence from cooking fuel. Measured NOx and CO fluxes were then compared to the MEIC 2013 emissions inventory, which was found to significantly overestimate emissions for this region, providing evidence that proxy-based emissions inventories have positive biases in urban centres. This first set of pollutant fluxes measured in Beijing provides an important benchmark of emissions from the city which can help to inform and evaluate current emissions inventories. [ABSTRACT FROM AUTHOR]

Isoprene (C5H8) emissions by terrestrial vegetation vary with temperature and light intensity, and play an important role in biosphere–chemistry–climate interactions. Such interactions were probably substantially modified by Pleistocene climate and CO2 cycles. Central to understanding the nature of these modifications is assessment and analysis of how emissions changed under glacial environmental conditions. Currently, even the net direction of change is difficult to predict because a CO2-depleted atmosphere may have stimulated emissions compensating for the negative impacts of a cooler climate. Here, we address this issue and attempt to determine the direction of change from an experimental standpoint by investigating the interaction between isoprene emissions and plant growth of two known isoprene-emitting herbaceous species (Mucuna pruriensandArundo donax) grown at glacial (180 ppm) to present (366 ppm) CO2 levels. We found a significant enhancement of isoprene emissions per unit leaf area inM. pruriensunder subambient CO2 concentrations relative to ambient controls but not forA. donax. In contrast, canopy emissions remained unaltered for both plant species because enhanced leaf emissions were offset by reductions in biomass and leaf area. Separate growth experiments withM. pruriensrevealed that lowering day/night temperatures by 5°C decreased canopy isoprene emissions irrespective of the CO2 level. Incorporation of these results into a simple canopy emissions model highlights their potential to attenuate reductions in the total isoprene flux from forests under glacial conditions predicted by standard models. [ABSTRACT FROM AUTHOR]

Describes the polynuclear aromatic hydrocarbons (PAH) deposition in air adjacent to two inland water bodies in Great Britain. Experiences of increased atmospheric loadings of suspended particulates; Indications of particle size distribution; Effect of precipitation on air concentrations and phase distributions; Impact of PAH volatilization.

Investigates the effect of ozone on four adsorbents and hydrocarbons adsorbed on Tenax-GR during passive sampling of air. Tenax-TA; Tenax-GR; Carbotrap; Chromosorb 106; Effect of ozone on adsorbents during passive sampling; Effect of ozone on organic compounds adsorbed on adsorbents during passive sampling.

The atmospheric composition of trace gases and aerosols is determined by the emission of compounds from the marine and terrestrial biospheres, anthropogenic sources and their chemistry and deposition processes. Biogenic emissions depend upon physiological processes and climate, and the atmospheric chemistry is governed by climate and feedbacks involving greenhouse gases themselves. Understanding and predicting the biogeochemistry of trace gases in past, present and future climates therefore demands an interdisciplinary approach integrating across physiology, atmospheric chemistry, physics and meteorology. Here, we highlight critical issues raised by recent findings in all of these key areas to provide a framework for better understanding the past and possible future evolution of the atmosphere. Incorporating recent experimental and observational findings, especially the influence of CO2 on trace gas emissions from marine algae and terrestrial plants, into earth system models remains a major research priority. As we move towards this goal, archives of the concentration and isotopes of N2O and CH4 from polar ice cores extending back over 650,000 years will provide a valuable benchmark for evaluating such models. In the Pre-Quaternary, synthesis of theoretical modelling with geochemical and palaeontological evidence is also uncovering the roles played by trace gases in episodes of abrupt climatic warming and ozone depletion. Finally, observations and palaeorecords across a range of timescales allow assessment of the Earth's climate sensitivity, a metric influencing our ability to decide what constitutes 'dangerous' climate change.