A minute fraction of atmospheric particles exert a disproportionate effect on the phase of mixed-phase clouds by acting as ice-nucleating particles (INPs). To understand the effects of these particles on weather and climate, both now and into the future, we must first develop a quantitative understanding of the major INP sources worldwide. Previous work has demonstrated that aerosols such as desert dusts are globally important INPs, but the role of biogenic INPs is unclear, with conflicting evidence for their importance. Here, we show that at a temperate site all INPs active above −18 °C at concentrations >0.1 L−1 are destroyed on heating, consistent with these INPs being of biological origin. Furthermore, we show that a global model of desert dust INPs dramatically underestimates the measured INP concentrations, but is consistent with the thermally-stable component. Notably, the heat sensitive INPs are active at temperatures where shallow cloud layers in Northern Europe are frequently observed to glaciate. Hence, we suggest that biogenic material is important for primary ice production in this region. The prevalence of heat sensitive, most likely biogenic, INPs in this region highlights that, as a community, we need to quantify the sources and transport of these particles as well as determine their atmospheric abundance across the globe and at cloud altitudes.

Abstract. Atmospheric aerosol particles are important for our planet's climate because they interact with radiation and clouds. Hence, having characterised methods to collect aerosol from aircraft for detailed offline analysis are valuable. However, collecting aerosol, particularly coarse-mode aerosol, onto substrates from a fast-moving aircraft is challenging and can result in both losses and enhancement in particles. Here we present the characterisation of an inlet system designed for collection of aerosol onto filters on board the Facility for Airborne Atmospheric Measurements (FAAM) BAe-146-301 Atmospheric Research Aircraft. We also present an offline scanning electron microscopy (SEM) technique for quantifying both the size distribution and size-resolved composition of the collected aerosol. We use this SEM technique in parallel with online underwing optical probes in order to experimentally characterise the efficiency of the inlet system. We find that the coarse-mode aerosol is sub-isokinetically enhanced, with a peak enhancement at around 10 µm up to a factor of 2 under recommended operating conditions. Calculations show that the efficiency of collection then decreases rapidly at larger sizes. In order to minimise the isokinetic enhancement of coarse-mode aerosol, we recommend sampling with total flow rates above 50 L min−1; operating the inlet with the bypass fully open helps achieve this by increasing the flow rate through the inlet nozzle. With the inlet characterised, we also present single-particle chemical information obtained from X-ray spectroscopy analysis, which allows us to group the particles into composition categories.

Cytochrome c has been immobilized onto functionalized, optically transparent indium tin oxide (ITO) electrodes by covalent and electrostatic techniques. Covalent immobilization was achieved by the formation of a disulfide bond between N-succinimidyl 3-(2-pyridyldithio)propionate-(SPDP-) modified cytochrome c and SPDP-silanized ITO. Additionally, ITO electrodes have been modified with the bifunctional reagent 1,12-dodecanedicarboxylic acid (DDCA), resulting in formation of a carboxylic acid-terminated monolayer. Covalent protein attachment to the DDCA-functionalized ITO was achieved with the cross-linker 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride. Electrostatic attachment of the protein involved ion-pair and hydrogen-bond interactions between the terminating carboxylic acid groups of the DDCA-functionalized ITO and the primary amine groups of the lysine residues of cytochrome c. The electrostatic interaction between the cytochrome c and the functionalized ITO resulted in greater rotational mobility of the protein at the electrode surface, leading to ca. 63% electroactivity, as compared to ca. 41% electroactivity for the covalently immobilized protein. The redox state of the electrostatically bound cytochrome c monolayers could be electrochemically switched between ferric and ferrous forms. Electrochemical control of the bound protein was used to regenerate the biosensing surface following binding of nitric oxide (NO). Ligation of NO with the cytochrome c was monitored by measurement of the change of absorbance intensity at 416 nm. Through application of a negative potential, the cytochrome c was reduced from the ferric to the ferrous form, which led to the removal of the ligated NO. Application of a positive potential regenerated the ferric cytochrome c, enabling multiple repeat measurements of NO. Such electrochemical control of proteins immobilized on transparent electrodes enables the optical biosensing of analyte targets without recourse to exogenous reagents.

11Atmospheric aerosol particles are important for our planet's climate because they interact with 12 radiation and clouds. Hence, having characterised methods to collect aerosol from aircraft for detailed 13 offline analysis are valuable. However, collecting aerosol, particularly coarse mode aerosol, onto 14substrates from a fast moving aircraft is challenging and can result in both losses and enhancement in 15 aerosol. Here we present the characterisation of an inlet system designed for collection of aerosol 16 onto filters on board the UK's BAe 146 Facility for Airborne Atmospheric Measurements (FAAM) 17research aircraft. We also present an offline Scanning Electron Microscopy (SEM) technique for 18 quantifying both the size distribution and size resolved composition of the collected aerosol. We use 19 this SEM technique in parallel with online underwing optical probes in order to experimentally 20 characterise the efficiency of the inlet system. We find that the coarse mode aerosol is sub-21 isokinetically enhanced, with a peak enhancement at around 10 μm up to a factor of three under 22 typical operating conditions. Calculations show that the efficiency of collection then decreases rapidly 23 at larger sizes. In order to minimise the isokinetic enhancement of coarse mode aerosol we 24 recommend sampling with total flow rates above 50 L min -1 ; operating the inlet with the bypass fully 25 open helps achieve this by increasing the flow rate through the inlet nozzle. With the inlet 26 characterised, we also present single particle chemical information obtained from X-ray spectroscopy 27 analysis which allows us to group the particles into composition categories. Our intention is to use the 28 composition information in parallel with filter based ice nucleating particle measurements in order to 29 correlate composition and ice nucleating particle concentrations. 30 31 Atmos. Meas. Tech. Discuss., https://doi.

No abstract