The determination of highly time resolved and source separated black carbon emission rates using radon as a tracer of atmospheric dynamics

Abstract

Abstract. We present a new method for the determination of the source specific black carbon emission rates. The methodology was applied in two different environments: an urban location in Ljubljana and a rural one in the Vipava valley (Slovenia, Europe), which differ in pollution sources and topography. The atmospheric dynamics was quantified using the atmospheric radon (222Rn) concentration to determine the mixing layer height for periods of thermally driven planetary boundary layer evolution. The black carbon emission rate was determined using an improved box model taking into account boundary layer depth and a horizontal advection term, describing the temporal and spatial exponential decay of black carbon concentration. The rural Vipava valley is impacted by a significantly higher contribution to black carbon concentration from biomass burning during winter (62 %) in comparison to Ljubljana (31 %). Results of the calculated black carbon emission rates in Ljubljana were in the range from 280 to 300 μg m−2 h−1 in spring and winter, respectively. Overall black carbon emission rate in Vipava valley were only 25 % lower compared to Ljubljana and were in the range from 210 to 240 μg m−2 h−1 in spring and winter, respectively. As expected, black carbon emissions from traffic prevail in Ljubljana and account for 80 % of emissions during winter; the traffic contribution in the Vipava valley was only 42 %. Different daily dynamics of biomass burning and traffic emissions was responsible for higher contribution of biomass burning to measured black carbon concentration, compared to the fraction of its emission rate. Coupling the high time resolution measurements of black carbon concentration with atmospheric radon concentration measurements can provide a useful tool for direct, highly time resolved measurements of the intensity of emission sources. Source specific emission rates can be used to assess the efficiency of pollution mitigation measures over longer time periods, thereby avoiding the influence of variable meteorology.