Abstract
Abstract. A synthesis of UK based airborne in-situ measurements of aerosol properties representing air masses from North-West Europe and the North-East Atlantic is presented. The major focus of the study is the vertical distribution of sub-micron aerosol chemical composition. Vertical profiles are derived from a Quadrupole Aerosol Mass Spectrometer (Q-AMS). Background sub-micron aerosol vertical profiles are identified and are primarily composed of organic matter and sulphate aerosol. Such background conditions occurred predominantly during periods associated with long-range air mass transport across the Atlantic. These instances may serve as useful model input of aerosol to Western Europe. Increased mass concentration episodes are coincident with European outflow and periods of stagnant/recirculating air masses. Such periods are characterised by significantly enhanced concentrations of nitrate aerosol relative to those of organic matter and sulphate. Periods of enhanced ground level PM2.5 loadings are coincident with instances of high nitrate mass fractions measured on-board the aircraft, indicating that nitrate is a significant contributor to regional pollution episodes. The vertical structure of the sulphate and organic aerosol profiles were shown to be primarily driven by large-scale dynamical processes. The vertical distribution of nitrate is likely determined by both dynamic and thermodynamic processes, with chemical partitioning of gas phase precursors to the particle phase occurring at lower temperatures at the top of the boundary layer. Such effects have profound implications for the aerosol's lifetime and subsequent impacts, highlighting the requirement for accurate representation of the aerosol vertical distribution.
Highlights
Uncertainty surrounding the impact of atmospheric aerosol is a major barrier to accurate prediction of future anthropogenically induced climate change (Forster et al, 2007)
Size distributions from the PCASP were available on 82 Straight Level Runs (SLRs)
The vertical distribution of aerosol chemical composition has been characterised for the UK region
Summary
Uncertainty surrounding the impact of atmospheric aerosol is a major barrier to accurate prediction of future anthropogenically induced climate change (Forster et al, 2007). The AeroCom exercise (Kinne et al, 2006; Schulz et al, 2006; Textor et al, 2006) established significant differences between participating models in terms of vertical aerosol dispersion (Textor et al, 2006) This variance contributes significantly to uncertainties in estimates of aerosol lifetimes in the atmosphere, which in turn impacts their climate effect. Novel online techniques are required to accurately measure the vertical distribution of aerosol composition Examples of such instruments are the Particle-Into-Liquid Sampler (PILS, Weber et al, 2001) and the Aerodyne Aerosol Mass Spectrometer (AMS, Jayne et al, 2000; Canagaratna et al, 2007). Dynamical processes control the advection of aerosol and their precursors to the sampling region This has been shown to modify the concentration and relative distribution of chemical species of sub-micron aerosol in the planetary boundary layer High pollution episodes identified via the UK ground based measurement network will be examined using the aircraft data coupled with the back trajectory analysis
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