On spatial scales of local aerosol production in boreal ecosystems

Abstract. Quantification of the climate impact of land use is important for the development of effective climate change mitigation and adaptation practices. Ecosystems emit compounds that participate in the formation and growth of aerosol particles. Particles of few nm size can be produced locally as compared to regional aerosol growth processes at larger sizes, and in boreal environment, higher concentrations of small particles were observed over agricultural lands than over forests. The aim of this study is to provide estimates of spatial scales of an ecosystem needed to produce small particles predominantly from own emissions. Here, we consider forest and agricultural ecosystems, and distinguish situations in which aerosol production is relatively slow and vertically distributed within the well-mixed boundary layer and when it can occur quickly close to the surface. For the latter, we introduce source contribution function of local aerosol production, which is based on the concentration footprint function modified to account for aerosol growth. We quantify the contributing area for neutral stratification and a typical wind speed. For below-canopy forest, the relevant distance is at 100–500 m, whereas it is at 0.9–5.5 km in agricultural fields, depending on the growth rate and the initial size distribution. For the distribution close to measurements, the contribution of the nearby 100–500 m is approximately 30 % in agricultural fields. To improve estimates, more research is needed on the dynamics of small aerosol, including contributions of chemical compounds to aerosol growth and the impact of meteorological conditions.