Abstract
Aerosol particles cool the climate by scattering solar radiation and by acting as cloud condensation nuclei. Higher temperatures resulting from increased greenhouse gas levels have been suggested to lead to increased biogenic secondary organic aerosol and cloud condensation nuclei concentrations creating a negative climate feedback mechanism. Here, we present direct observations on this feedback mechanism utilizing collocated long term aerosol chemical composition measurements and remote sensing observations on aerosol and cloud properties. Summer time organic aerosol loadings showed a clear increase with temperature, with simultaneous increase in cloud condensation nuclei concentration in a boreal forest environment. Remote sensing observations revealed a change in cloud properties with an increase in cloud reflectivity in concert with increasing organic aerosol loadings in the area. The results provide direct observational evidence on the significance of this negative climate feedback mechanism.
Highlights
Aerosol particles cool the climate by scattering solar radiation and by acting as cloud condensation nuclei
We investigate the “biogenic secondary organic aerosol (BSOA) driven feedback” at a boreal site by studying the relationship between organic aerosol loadings of biogenic origin and temperature, and further the consequences on direct and indirect aerosol effects using field and remote sensing observations
Our analysis was based on observations from summertime when the precursor concentrations and likely BSOA-driven climate feedback are at their annual maximum[16,17]
Summary
Aerosol particles cool the climate by scattering solar radiation and by acting as cloud condensation nuclei. Paasonen et al.[17] observed increasing number concentration of CCN-sized particles with increasing temperature at several measurement sites, while direct evidence on the link to organic aerosol formation lacked, and some previous studies report an increase in aerosol optical thickness with temperature above forested area[18,19]. When these steps are put together in climate models, simulations predict such feedback[14]. Our results provide observation-based evidence for full BSOA-driven feedback cycle starting from temperaturedriven increase in organic aerosol mass, continuing to increasing CCN concentration, and to cloud physical and radiative properties
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