Measurement report: Three years of size-resolved eddy-covariance particle number flux measurements in an urban environment

Straaten, Agnes; Weber, Stephan

Size-resolved particle number fluxes in the size range of 10 nm inline-formula< particle diameter (inline-formulaDp) inline-formula< 200 nm were measured over a 3-year period (April 2017–March 2020) using the eddy-covariance technique at an urban site in Berlin, Germany. The observations indicated the site as a net source of particles with a median total particle number flux of inline-formulaFTNC=0.86inline-formula× 10inline-formula8 minline-formula−2 sinline-formula−1. The turbulent surface–atmosphere exchange of particles was clearly dominated by ultrafine particles (inline-formulaDpinline-formula< 100 nm) with a share of 96 % of total particle number flux (inline-formulaFUFP=0.83 inline-formula× 10inline-formula8 minline-formula−2 sinline-formula−1).

Annual estimates of median inline-formulaFTNC and inline-formulaFUFP slightly decreased by inline-formula−9.6 % (inline-formula−8.9 % for inline-formulaFUFP) from the first to the second observation year and a further inline-formula−5.9 % (inline-formula−6.1 % for inline-formulaFUFP) from the second to the third year. The annual variation might be due to different reasons such as the variation of flux footprints in the individual years, a slight reduction of traffic intensity in the third year, or a progressive transition of the vehicle fleet towards a higher share of low-emission standards or electric drive. Size-resolved measurements illustrated events of bidirectional fluxes, i.e. simultaneous emission and deposition fluxes within the size spectrum, which occurred more often in spring, late summer, and autumn than in winter. Multi-year observations of size-resolved particle fluxes proved to be important for a deeper understanding of particle exchange processes with the urban surface and the pronounced influence of traffic at this urban site.

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Straaten, Agnes / Weber, Stephan: Measurement report: Three years of size-resolved eddy-covariance particle number flux measurements in an urban environment. 2021. Copernicus Publications.

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