Abstract
Abstract. We investigated the natural aerosol evolution of biogenic monoterpene emissions over the northern boreal forest area as a function of temperature using long-term field measurements of aerosol size distributions and back trajectories at two SMEAR (Station for Measuring Ecosystem–Atmosphere Relations) stations, SMEAR I and SMEAR II, in Finland. Similar to earlier studies, we found that new particles were formed via nucleation when originally clean air from the ocean entered the land, after which these particles continuously grew to larger sizes during the air mass transport. Both the travelling hour over land and temperature influenced the evolution of the particle number size distribution and aerosol mass yield from biogenic emissions. Average concentrations of nucleation mode particles were higher at lower temperatures, whereas the opposite was true for accumulation mode particles. Thus, more cloud condensation nuclei (CCN) may be formed at higher temperatures. The overall apparent aerosol yield, derived from the aerosol masses against accumulated monoterpene emissions, ranges from 13 to 37% with a minor, yet complicating, temperature dependence.
Highlights
Natural aerosol particles – including sea spray, mineral dust, and primary and secondary biogenic particles – are central to our understanding of the earth’s climate system (Carslaw et al, 2010)
We extended earlier studies to evaluate the potential temperature impacts on the natural aerosol dynamics and mass yield from biogenic momoterpene emissions among northern boreal forest area, using long-term field measurements of aerosol size distributions and back trajectories at two Finnish SMEAR stations
We found that nucleation prefers to take place in originally clean marine air masses after they have arrived at the boreal forest area
Summary
Natural aerosol particles – including sea spray, mineral dust, and primary and secondary biogenic particles – are central to our understanding of the earth’s climate system (Carslaw et al, 2010). This is, first of all, because the atmospheric concentration levels and properties of natural aerosols need to be known in order to determine which fraction of the atmospheric aerosol is of anthropogenic origin. Since potential BSOA precursor emissions from terrestrial ecosystems strongly increase with increasing temperatures (Guenther et al, 2012), the natural CCN production associated with BSOA may be enhanced in warmer future climate, which would lead to a negative climate feedback mechanism (Kulmala et al, 2004). A major reason for this is that the temperature influences the BSOA precursor emissions, and their atmospheric oxidation, resulting
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