Richard T. Lidster

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...

The application of two total transfer valve modulators for comprehensive two‐dimensional gas chromatography of volatile organic compounds

Rotary and diaphragm 6-port 2-position valves have been evaluated as modulators for comprehensive GC. A total transfer methodology was used such that all analyte materials from the primary column were passed to the second separating column. The transfer methodology used repeated short periods of stop flow, but retained good primary column performance since primary carrier flow was partially maintained as pressure equilibrated along the length of the first column. Highly resolved separations of complex samples such as petrol and essential oils were achieved with equivalent performance (in terms of second column resolution) to thermal modulation with flame ionisation detection (FID). The valve modulators tested could outperform thermal modulators for very highly volatile organic species since the modulation process was insensitive to analyte vapour pressure. The diaphragm valve tested showed the best performance and was incorporated with a thermal desorption system to provide a high sensitivity separation of volatile organic compounds (VOCs) in air with LODs for individual VOCs of 2-4  pptV for a 1-L air sample.

A compact comprehensive two-dimensional gas chromatography (GC×GC) approach for the analysis of biogenic VOCs

We describe the development of a compact comprehensive two-dimensional gas chromatograph suitable for the measurement of biogenic VOCs in the atmosphere at part per billion mixing ratios. The design seeks to minimise instrument size and power consumption and maximise portability and autonomy. The instrument concept is to achieve high analyte selectivity for complex VOC mixture analysis using comprehensive two-dimensional GC (GC×GC), rather than hyphenation with larger more expensive detectors such as MS. Key features of the analytical approach are a custom-built miniature thermal desorption trap to collect and concentrate VOCs from the sample gas stream, a copper conducting direct column heating system and a valve-modulated interface to enable GC×GC. The high power and large form-factor turbulent GC oven is replaced by direct column heating (and cooling below ambient) by thermal transfer from copper bobbin holders with heating and cooling input from Peltier devices. The combination of two independent copper bobbins allows for independent control of the two columns needed for comprehensive GC. A heated two position 1/16′′ diaphragm valve is used to enable flow modulation between two columns, with analyte detection at the outlet of the second column using a miniaturised low cost photo-ionisation detector. The instrument sub-components are controlled by a Compact RIO computer (National Instruments) and purpose designed software written in LabVIEW allowing autonomous measurements. The complete system weighs 15 kg, is around the size of a desktop computer and has a mean power demand of 112 W when battery powered. Results on the sensitivity and linearity for isoprene collection and analysis of standard gas mixtures are presented along with a discussion of limiting factors that hinder field device performance.

Improving the Quantification of Secondary Organic Aerosol Using a Microflow Reactor Coupled to HPLC-MS and NMR to Manufacture Ad Hoc Calibration Standards

Secondary organic aerosol (SOA) is a key uncertainty in quantifying the impact of humans on Earths climate. SOA is a complex mixture of oxidized organic species, and a fundamental hurdle in determining its composition is the lack of authentic standards for comparison and quantification. Organic synthesis can be used to produce pure standards, but is limited to compounds for which there is a degree of confidence in the proposed structure and can be expensive and time-consuming. In this study, a flow reactor was developed to form SOA in sufficient quantities to be collected and pure compounds subsequently isolated from the mixture using semipreparative high performance liquid chromatography. The purity and yield of each isolated compound were obtained using proton nuclear magnetic resonance ((1)H NMR), whereas molecular formulas were confirmed by high resolution Fourier transform ion cyclotron mass spectrometry (FTICR-MS). The effectiveness of the methodology has been evaluated here by using α-pinene as the precursor because it is the monoterpene with the most well characterized SOA chemistry. Eleven individual α-pinene SOA compounds were produced from α-pinene oxidation experiments and used for quantitative analysis of SOA formed during chamber experiments carried out close to ambient conditions. These compounds represented 25% of the total SOA mass, a significant improvement in mass balance compared to previous studies. This relatively simple approach may be extended to produce other SOA components not available commercially to improve quantification of aerosol sources.