Measurement Report: New particle formation characteristics at an urban and a mountain station in Northern China

Abstract. Atmospheric new particle formation (NPF) events have attracted increasing attention for their contribution to the global aerosol number budget, and therefore their effects on climate, air quality, and human health. NPF events are regarded as a regional phenomenon, occurring over a large area. However, the spatial variation of NPF intensity has not been investigated in detail by incorporating both urban and regional measurements. Urban environments have more heterogeneous and freshly emitted NPF precursors as compared to environments with less anthropogenic activity. Here, we provide a comparison of NPF event characteristics – NPF event frequency, particle formation rate, and growth rate – by comparing an urban Beijing site and a background mountain site separated by ~80 km from June 14 to July 14, 2019 as well as give insights into the connection between both locations. During the measurement period, 12 and 13 NPF events were observed at the urban and background mountain sites, respectively, with 9 NPF events observed on the same day at both sites. Although the median condensation sink during the first two hours of the common NPF events was around 0.01 s−1 at both sites, there were notable differences in particle formation rates between the two locations (median of 5.42 cm−3 s−1 at the urban site and 1.13 cm−3 s−1 at the mountain site during the first two hours of common NPF events). Yet, the particle growth rates in the 7–15 nm range for common NPF events were comparable (median of 7.6 nm.h−1 at the urban site and 6.5 nm.h−1 at the mountain site as median values). To understand whether the observed events were connected, we compared air mass trajectories as well as meteorological conditions at both stations. Favorable conditions for the occurrence of regional NPF events were largely affected by air mass transport. Overall, our results demonstrate a clear inhomogeneity of regional NPF within a distance of ~100 km, which should be considered in regional-scale aerosol models when estimating the budget of aerosol load and cloud condensation nuclei.