International audienc

In early spring the Baltic region is frequently affected by high-pollution events due to biomass burning in that area. Here we present a comprehensive study to investigate the impact of biomass/grass burning (BB) on the evolution and composition of aerosol in Preila, Lithuania, during springtime open fires. Non-refractory submicron particulate matter (NR-PM 1 ) was measured by an Aerodyne aerosol chemical speciation monitor (ACSM) and a source apportionment with the multilinear engine (ME-2) running the positive matrix factorization (PMF) model was applied to the organic aerosol fraction to investigate the impact of biomass/grass burning. Satellite observations over regions of biomass burning activity supported the results and identification of air mass transport to the area of investigation. Sharp increases in biomass burning tracers, such as levoglucosan up to 683 ng m −3 and black carbon (BC) up to 17 µg m −3 were observed during this period. A further separation between fossil and non-fossil primary and secondary contributions was obtained by coupling ACSM PMF results and radiocarbon ( 14 C) measurements of the elemental (EC) and organic (OC) carbon fractions. Non-fossil organic carbon (OC nf ) was the dominant fraction of PM 1 , with the primary (POC nf ) and secondary (SOC nf ) fractions contributing 26-44 % and 13-23 % to the total carbon (TC), respectively. 5-8 % of the TC had a primary fossil origin (POC f ), whereas the contribution of fossil secondary organic carbon (SOC f ) was 4-13 %. Nonfossil EC (EC nf ) and fossil EC (EC f ) ranged from 13-24 and 7-13 %, respectively. Isotope ratios of stable carbon and nitrogen isotopes were used to distinguish aerosol particles associated with solid and liquid fossil fuel burning. Published by CopernicusPublications on behalf of the European Geosciences Union. 5514 V. Ulevicius et al.: Fossil and non-fossil source contributions to atmospheric carbonaceous aerosols

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Predicted climate changings can affect hemi-boreal forests especially for soil conditions with low water-holding capacity and susceptibility to soil water deficits. In our study, species-specific sap flux, transpiration and water use efficiency of growth WUE were investigated at a mixed hemi-boreal forest ecosystems, especially during temporary moderate dry periods in the main growing season. Therefore, two representative forest sites with different drought susceptibility were selected in Northwest-Lithuania. The aim of our investigations was to identify the responsible factors influencing transpiration and WUE from Scots pine Pinus sylvestris L. , Norway spruce Picea abies L. H. Karst. and birch silver birch: Betula pendula Roth. and downy birch: B. pubescens Ehrh. during temporary drought incidents at a water-limited, oligitrophic sand dominated forest site and at a water saturated, mesoeutrophic organic peat forest site for the whole vegetation period and two moderate short-term drought incidents in 2016. During the dry periods Norway spruce trees exhibited lowest sap flux compared to Scot pine and birch while similarly showing highest WUE. Up-scaled to a virtual pure stand none of the species were differing in species specific transpiration. Thus, we found no evidence for extended drought sensitivity of Norway spruce at the water limited site during the first investigation year. Sap flux of Scots pine trees was more or less constantly high during the main growing season and the dry periods at both plots, while WUE was quite low during the "dry periods". Thus, we assume that Scots pine trees are less affected by temporarily drought events than Norway spruce. Birch trees exhibited significantly highest sap flux during dry periods at the water limited site whereas quite low WUE was not differing between sites. Thus, birch may compete with Scots pine trees at the study sites in terms of water consumption and growth in future.

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