Strategic Aerosol Observation and Modelling Capacities for Northern and Polar Climate and Pollution

Atmospheric aerosol particles influence climate by scattering incoming solar radiation back into space (direct climate effect, cooling), and absorbing infrared radiation emitted by the Earth surface, thus heating the atmosphere (semi-direct effect, warming). They also influence climate by increasing cloud reflectivity and lifetime (indirect effect, cooling). They can adversely affect human health by influencing the respiratory and cardiovascular system. The project addresses these challenges in the context of the research priorities defined by the Norwegian Environment Agency and the Norwegian Research Council: WP1: Observations Tailored to Assessing the Indirect Aerosol Climate Effect Insufficient understanding of the indirect aerosol climate effect is one of the most significant causes for the uncertainty in current climate predictions. Climate models need constraining data on the number of cloud condensation nuclei (CCN) to reduce their uncertainty. To achieve this for continental Norway and elsewhere, this WP established these observations at Birkenes observatory in Southern Norway, and collects the corresponding data from stations in Europe and around the globe. A corresponding instrument, a CCN counter (CCNC), was taken into operation at Birkenes, matching data reporting routines for stations around the globe to the WMO World Data Centre for Aerosol at NILU were established, the first years of data were collected. During the present reporting period, an overview publication was initialised in collaboration with the EU-FP7 research infrastructure ACTRIS. The publication plans to summarise these observations across Europe, and relate them to collocated measurements of online aerosol chemical composition. This will facilitate the intended use of the data for improving the respective processes in climate models and reduce model uncertainty. WP2: Global Transport Pathways of Particle-Bound Air Pollution with Focus on Southern Polar Latitudes Changes in climate become visible first at high and polar latitudes as compared to lower latitudes. With a national territory largely located at high latitudes and with a focus on climate research, Norwegian authorities emphasize polar climate research. This WP addresses this emphasis by investigating data on aerosol properties collected at the NILU operated atmospheric observatory at Norway's Antarctic station Troll. Subject was the synchronous annual cycle in the baseline of physical (particle number size distribution) and optical (scattering coefficient) aerosol properties. The analysis showed that Central Antarctic baseline air (ABA) is transported upward at mid-latitudes or in the tropics, transported to Antarctica in the upper free troposphere or lower stratosphere, and descends over Central Antarctica. The aerosol particles in ABA are largely produced by photochemical oxidation of precursor substances during this transport. The analysis facilitates a better understanding of natural versus anthropogenic aerosol processes. It will contribute to a better distinction between natural and man-made climate change (Fiebig et al., Atmos. Chem Phys. 14(6), 3083-3093, 2014). Following a successful NFR proposal, future work will try to collect filter samples of ABA in order to understand its sources, natural or anthropogenic. WP3: Past, Present, and Future Air Pollution Transport to Norway Source attributions of climate forcing agents and pollutants are a prerequisite for emission policies. The atmospheric observatory at Birkenes in Southern Norway has been upgraded with observations of microphysical, optical, and chemical atmospheric aerosol properties (EMEP supersite and WMO GAW station in 2009). In this WP, the set of observed aerosol properties is extended by the levoglucosan concentration, a tracer for biomass burning. During the reporting period, a cluster analysis was finished for the years 2010-2012 to group the data by similarity and to determine the dominating air mass types, assisted by cluster specific transport modelling to identify source regions. The analysis yielded 8 air mass types, including some with very well defined source regions in continental Europe, but also polar marine air masses, and those dominated by domestic heating (winter) or biogenic aerosol production (summer). It was shown that aerosol parameters with high time resolution (optical properties, particle size distribution), contain maximum achievable information on air mass type. The inclusion of aerosol chemical composition data did not result in further information on air mass type because of much lower time resolution (one day vs. one hour) of these data. As intended, the transport model FLEXPART was coupled to the NorESM climate model to extend this climatology into the future; a publication on this issue is in preparation.

Atmospheric aerosol is an important agent in climate forcing, air quality, and health. Several of the related issues have been prioritised in national Norwegian research strategies, and SACC will target three of them. The first focus will be on aerosol-cl oud interaction, the largest source of uncertainty in current climate predictions, especially at boreal and polar latitudes with frequent cloud cover. Since the main source for this uncertainty is lack of corresponding long-term observations, the project will install this capacity at the EMEP supersite Birkenes, and connect these observations at Zeppelin Mountain to international networks. The data will be analysed into a form readily usable by climate models to improve climate predictions for Norway, bor eal, polar latitudes. The second focus continues the successful IPY efforts at Norway's Antarctic station Troll. Based on the aerosol observations at Troll, a climatology of transport through the boundary layer and upper troposphere / lower stratosphere w ill be established as a benchmark test for aerosol representation in climate models, thus improving these. Using climate predictions and transport modelling, the climatology will be extended into the future to allow for pollution mitigation strategies in this climate sensitive region. In the third focus, the project will reanalyse archived aerosol filter samples collected at Birkenes observatory with modern methods for obtaining an improved source apportionment of air pollution reaching Norway. This sourc e apportionment will be extended into the future by dispersion transport modelling driven by climate predictions. This will allow for advance adaption planning of this aspect of climate change. The project will contribute to better climate predictions for Norway and polar latitudes, meeting and adapting to climate change, improve Norwegian atmospheric research infrastructure, and feed into Norway's contributions to international frameworks (EMEP, WMO GAW).