Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 12659-12675, 2017
https://doi.org/10.5194/acp-17-12659-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
25 Oct 2017
A new balance formula to estimate new particle formation rate: reevaluating the effect of coagulation scavenging
Runlong Cai and Jingkun Jiang State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China
Abstract. A new balance formula to estimate new particle formation rate is proposed. It is derived from the aerosol general dynamic equation in the discrete form and then converted into an approximately continuous form for analyzing data from new particle formation (NPF) field campaigns. The new formula corrects the underestimation of the coagulation scavenging effect that occurred in the previously used formulae. It also clarifies the criteria for determining the upper size bound in measured aerosol size distributions for estimating new particle formation rate. An NPF field campaign was carried out from 7 March to 7 April 2016 in urban Beijing, and a diethylene glycol scanning mobility particle spectrometer equipped with a miniature cylindrical differential mobility analyzer was used to measure aerosol size distributions down to ∼ 1 nm. Eleven typical NPF events were observed during this period. Measured aerosol size distributions from 1 nm to 10 µm were used to test the new formula and the formulae widely used in the literature. The previously used formulae that perform well in a relatively clean atmosphere in which nucleation intensity is not strong were found to underestimate the comparatively high new particle formation rate in urban Beijing because of their underestimation or neglect of the coagulation scavenging effect. The coagulation sink term is the governing component of the estimated formation rate in the observed NPF events in Beijing, and coagulation among newly formed particles contributes a large fraction to the coagulation sink term. Previously reported formation rates in Beijing and in other locations with intense NPF events might be underestimated because the coagulation scavenging effect was not fully considered; e.g., estimated formation rates of 1.5 nm particles in this campaign using the new formula are 1.3–4.3 times those estimated using the formula neglecting coagulation among particles in the nucleation mode.

Citation: Cai, R. and Jiang, J.: A new balance formula to estimate new particle formation rate: reevaluating the effect of coagulation scavenging, Atmos. Chem. Phys., 17, 12659-12675, https://doi.org/10.5194/acp-17-12659-2017, 2017.
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Short summary
Widely used formulae underestimate the atmospheric new particle formation (NPF) rate when intense NPF events are analyzed. This is caused by the underestimation or neglect of the coagulation scavenging effect. To address this issue, a new formula was theoretically derived. Aerosol down to ~ 1 nm was measured in Beijing and used together with data reported in the literature to test the new formula and others. Implications for NPF rates in various atmospheric environments are discussed.
Widely used formulae underestimate the atmospheric new particle formation (NPF) rate when...
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