Towards a UK Airborne Bioaerosol Climatology

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Primary biological aerosols (PBA), or bioaerosols, are a poorly understood component of organic carbonaceous aerosols (OC), contributing a significant fraction to airborne particulate matter (PM) and comprising mixtures of many thousands of organic compounds. PBA include live or dead cells and cell fragments, fungal spores and pollens, and plant, insect and animal fragments. They have a major influence on the physico-chemical, biological, health and even climate related behaviour of atmospheric aerosols and chemical processes. The detection, characterization and classification of these aerosols and their descriptions in atmospheric transport models has remained a major challenge to the science community. Indeed the US national Academies of Science concluded that "The overall understanding of their impacts on atmospheric composition, climate, and human health remains weak." (NAS, 2016). Global and regional bioaerosol (PBA) emission and transport modelling studies have demonstrated very large uncertainties and thus provide limited understanding of these important atmospheric constituents. This is primarily due to a lack lack of observational data on their fluxes and airborne concentrations for many different ecosystems. Important, as yet unanswered, questions raised recently include: the relative importance of continuous versus intermittent emission and transport of PBA to ambient concentrations and subsequent impacts; whether PBA significantly influence cloud and precipitation processes via the "bioprecipitation" hypothesis; the degree to which they can reproduce via atmospheric ecosystem niches from the tropics to the poles; and whether they can influence chemical processes through degradation of organic compounds. All recent studies and reviews have similarly concluded that in order to start to address the many and growing challenges associated with PBA we need to acquire a better knowledge of their atmospheric concentrations and distributions and in particular knowledge of their vertical concentration profiles. The most recent in depth review of PBA, Fröhlich-Nowoisky et al. (2016), concluded that "major challenges include the quantitative characterization of exchange between surface, planetary boundary layer, and free troposphere. For this purpose, ground based measurements have to be combined with tall tower and aircraft measurements... to obtain information on the vertical and horizontal distribution of bioparticles." We aim to do just this, delivering new data sets to enable emissions modelling for the UK environment. We will use existing measurement facilities on the NERC FAAM aircraft together with surface measurements to deliver vertical and horizontal PBA concentration profiles over UK regions including urban, rural-cropland, grassland, forest & coastal. We will use aircraft bioaerosol sampling methodologies recently developed in the US together with real-time bioaerosol instruments. These data will provide the first such information on UK boundary layer concentration profiles of bioaerosol for over 50 years. High quality UK airborne data sets suitable for constraining & testing UK bio-emissions models for the first time.Our new vertically & horizontally resolved PBA-climate database will support a raft of scientific research and policy applications well beyond the timescale of the project. In situ PBA concentrations will be correlated with airborne meteorological, trace gas and other aerosol composition data, for air mass classification, using tools developed for the FAAM aircraft over many years for source tracking & identification. This will allow us to deliver quality controlled, assimilation-ready case studies able to constrain a wide range of potential PBA emissions models. We will also conduct laboratory experiments to deliver UK specific bioaerosol reference data sets designed to improve interpretation of current and future PBA field data collected using real-time UVLIF bioaerosol instruments.