Am Booth

Meteorology, air quality, and health in London: The ClearfLo project

AbstractAir quality and heat are strong health drivers, and their accurate assessment and forecast are important in densely populated urban areas. However, the sources and processes leading to high concentrations of main pollutants, such as ozone, nitrogen dioxide, and fine and coarse particulate matter, in complex urban areas are not fully understood, limiting our ability to forecast air quality accurately. This paper introduces the Clean Air for London (ClearfLo; www.clearflo.ac.uk) project’s interdisciplinary approach to investigate the processes leading to poor air quality and elevated temperatures.Within ClearfLo, a large multi-institutional project funded by the U.K. Natural Environment Research Council (NERC), integrated measurements of meteorology and gaseous, and particulate composition/loading within the atmosphere of London, United Kingdom, were undertaken to understand the processes underlying poor air quality. Long-term measurement infrastructure installed at multiple levels (street and eleva...

Surface tension of mixed inorganic and dicarboxylic acid aqueous solutions at 298.15 K and their importance for cloud activation predictions

The following study extends previous work on modelling multicomponent surface tensions and the impact they have on aerosol and climate modelling. Mixed dicarboxylic acid and ammonium sulfate solution surface tensions have been measured experimentally and were modelled using an additive, a semi-empirical and two thermodynamic methods. A thermodynamic method with parameters fitted to binary solution data reproduced experimental results most closely with average absolute deviation from the experimental data over all measurements of 2.6%, compared with 7.7% for the additive, 8.1% for the semi-empirical and 7.3% for the other thermodynamic method. The choice of surface tension modelling method can lead to differences of up to 50% in the critical saturation ratios of aerosol particles. When applied to a trimodal aerosol distribution this leads to a difference in dry diameter for activation of 30 to 40 nm. This is greater than the difference induced by changing inorganic to organic mass ratios (>10 nm).

An assessment of vapour pressure estimation methods

Laboratory measurements of vapour pressures for atmospherically relevant compounds were collated and used to assess the accuracy of vapour pressure estimates generated by seven estimation methods and impacts on predicted secondary organic aerosol. Of the vapour pressure estimation methods that were applicable to all the test set compounds, the Lee-Kesler [Reid et al., The Properties of Gases and Liquids, 1987] method showed the lowest mean absolute error and the Nannoolal et al. [Nannoonal et al., Fluid Phase Equilib., 2008, 269, 117-133] method showed the lowest mean bias error (when both used normal boiling points estimated using the Nannoolal et al. [Nannoolal et al., Fluid Phase Equilib., 2004, 226, 45-63] method). The effect of varying vapour pressure estimation methods on secondary organic aerosol (SOA) mass loading and composition was investigated using an absorptive partitioning equilibrium model. The Myrdal and Yalkowsky [Myrdal and Yalkowsky, Ind. Eng. Chem. Res., 1997, 36, 2494-2499] vapour pressure estimation method using the Nannoolal et al. [Nannoolal et al., Fluid Phase Equilib., 2004, 226, 45-63] normal boiling point gave the most accurate estimation of SOA loading despite not being the most accurate for vapour pressures alone.

The role of ortho, meta, para isomerism in measured solid state and derived sub-cooled liquid vapour pressures of substituted benzoic acids

Knudsen Effusion Mass Spectrometry (KEMS) has been used to measure solid state equilibrium vapour pressures of several multifunctional aromatic compounds; phthalic, isophthalic, terephthalic, para-anisic, ortho-amino benzoic, meta-amino benzoic, para-amino benzoic, vanillic, syringic, 1,2,4-tricarboxylic benzoic, 3,5-dihydroxy-4-methyl benzoic and 4-methyl phthalic acids and nitrocatechol. Sub-cooled liquid vapour pressures were derived using Differential Scanning Calorimetry (DSC) measured thermochemical properties for the compounds measured here, as well as for other substituted benzoic acids using literature values. Unusual trends in the sub-cooled liquid vapour pressure, not represented by currently available vapour pressure estimation methods, are explained using a newly constructed Structure–Activity Relationship (SAR) with a combination of resonance and steric effects. This was then tested against further measurements of ortho-dimethyl amino benzoic and meta-dimethyl amino benzoic acids.