[1] Lidar observations of volcanic ash are reported, that have been obtained during six flights of the Facility for Airborne Atmospheric Measurements BAe-146 research aircraft over the United Kingdom and the surrounding seas in May 2010, after the eruption of Eyjafjallajökull. Due to safety restrictions, sampling has only been done in areas where forecasted concentrations were smaller than 2000 mg/m 3 . Aircraft in situ measurements of size-distribution permitted evaluation of a coarse extinction fraction (ranging 0.5-1) and a coarse mode specific extinction (0.6-0.9 m 2 /g) for each flight. These quantities were then used to convert the lidar-derived aerosol extinction to ash concentration (with an estimated uncertainty of a factor of two). The data highlight the very variable nature of the ash plume in both time and space, with layers 0.5-3 km deep observed between 2 and 8 km above sea level, and featuring an along-track horizontal extent of 85-550 km. Flights on 14-17 May showed typical concentrations of 300-650 mg/m 3 , and maxima of 800-1900 mg/m 3 in relatively small high density patches. Column loads for these flights were typically 0.25-0.5 g/m 2 (maxima 0.8-1.3 g/m 2 ). Relatively small regions characterized by a larger ash content have been selected, and the distribution of ash concentrations and column loadings within them proved rather broad, showing how fractal and patchy the observed ash layers are. A visual comparison of our data set with the "dust RGB" maps from SEVIRI showed a good spatial correlation for the larger ash content days. Moreover, ash prediction maps output from the NAME dispersion model show reasonable agreement with the overall magnitude of the observed concentrations; in some cases, however, there are positional errors in the predicted plume location, due to uncertainties in the eruption source details, driving meteorology, and in the model itself.

The Clean Air for London (ClearfLo) project provides integrated measurements of the meteorology, composition, and particulate loading of the urban atmosphere in London, United Kingdom, to improve predictive capability for air quality. METEOROLOGY, AIR QUALITY, AND HEALTH IN LONDONThe ClearfLo Project Economic and Social Affairs 2013). Urban populations are exposed to stressful environmental conditions, such as local and nonlocal pollutants, that cause poor air quality and microclimates that exacerbate heat stress during heat waves. These are projected to increase in a warming climate. Our cities are therefore nexus points for several environmental health stresses that we currently face (Rydin et al. 2012) and the interacting issues around sustainability and human health.The purpose of this paper is to introduce the Clean Air for London (ClearfLo) project, which investigates the atmospheric science that underpins these health stresses, with a particular focus on the urban increment in atmospheric drivers. We focused on three atmospheric drivers of environmental health stress in cities, namely, heat, gas-phase pollutants, and particulate matter (PM). Health stresses from the urban atmospheric environment.Heat waves have an impact on human health. Populations typically display an optimal temperature range at which the (daily or weekly) mortality rate is lowest. Mortality rates rise as temperatures exceed this optimal range (e.g., Rydin et al. 2012). The 2003 European heat wave (Stedman 2004) in combination with air pollution was responsible for more than 2000 excess deaths in the United Kingdom (Johnson et al. 2005). Under a warming climate, the risks posed by heat stress are predicted to increase (Hacker et al. 2005). People living in urban environments are exposed to higher temperatures than in nonurban regions. Thus, heat-related deaths could be higher within urban areas (Mavrogianni et al. 2011). Hence, ClearfLo is concerned with measuring the factors controlling the urban atmospheric boundary layer, that is, the surface energy balance.The World Health Organization (WHO) reported (WHO 2006) that the strongest effects of air quality 779MAY 2015 AMERICAN METEOROLOGICAL SOCIETY | on health are attributable to PM, followed by ozone (O 3 ) and nitrogen dioxide (NO 2 ). A recent report (Guerreiro et al. 2013) indicates that in 2011 up to 88% of the urban population in Europe was exposed to concentrations exceeding the WHO air quality guidelines for PM 10 (defined as particles that pass through a size-selective inlet with a 50% efficiency cutoff at 10-µm aerodynamic diameter, representative of the inhalable fraction). It is estimated that a reduction of PM 10 to the WHO annual-mean guideline of 20 µg m −3 would reduce attributable deaths per year in Europe by 22,000. Further, this would lead to a substantial improvement in the quality of life for millions with a preexisting respiratory or cardiovascular disease (COMEAP 2010).Epidemiological studies consistently demonstrate an association between the PM mass concentr...

To study why, where, and when deep convection

No abstract