Aerosol Surface Area Concentration: a Governing Factor for New Particle Formation in Beijing

Abstract

<p><strong>Abstract.</strong> The predominating role of aerosol Fuchs surface area, <i>A</i><sub>Fuchs</sub>, in determining the occurrence of new particle formation (NPF) events in Beijing was elucidated in this study. Analysis was based on a field campaign from March 12<sup>th</sup> to April 6<sup>th</sup>, 2016, in Beijing, during which aerosol size distributions down to ~ 1 nm and sulfuric acid concentration were simultaneously monitored. The 26 days were classified into 11 typical NPF days, 2 undefined days, and 13 non-event days. A dimensionless factor, <i>L</i><sub>Γ</sub>, characterizing the relative ratio of the coagulation scavenging rate over the condensational growth rate and predicting whether or not a NPF event would occur (Kuang et al., 2010), was applied. The three parameters determining <i>L</i><sub>Γ</sub> are sulfuric acid concentration, the growth enhancement factor characterizing contribution of other gaseous precursors to particle growth, Γ, and <i>A</i><sub>Fuchs</sub>. Different from other atmospheric environment such as in Boulder and Hyytiälä, the variations of daily maximum sulfuric acid concentration and Γ in Beijing are in a narrow range with geometric standard deviations of 1.40 and 1.31, respectively. Positive correlation was found between estimated new particle formation rate, <i>J</i><sub>1.5</sub>, and sulfuric acid concentration with a mean fitted exponent of 2.4. However, sulfuric acid concentration on NPF days is not significantly higher than that on non-event days. Instead, <i>A</i><sub>Fuchs</sub> varies greatly among days in Beijing with a geometric standard deviation of 2.56, while it is relatively stable at other locations such as Tecamac, Atlanta, and Boulder. Good correlation was found between <i>A</i><sub>Fuchs</sub> and <i>L</i><sub>Γ</sub> in Beijing (R<sup>2</sup> = 0.88). It appears that the abundance of gaseous precursors such as sulfuric acid in Beijing is high enough to have nucleation, however, it is <i>A</i><sub>Fuchs</sub> that determines the occurrence of NPF event in Beijing. 10 in 11 NPF events occurred when <i>A</i><sub>Fuchs</sub> is smaller than 200 μm<sup>2</sup>/cm<sup>3</sup>, and the NPF event was suppressed due to coagulation scavenging when <i>A</i><sub>Fuchs</sub> is larger than 200 μm<sup>2</sup>/cm<sup>3</sup>. Measured <i>A</i><sub>Fuchs</sub> is in good correlation with PM<sub>2.5</sub> mass concentration (R<sup>2</sup> = 0.85) since <i>A</i><sub>Fuchs</sub> in Beijing is mainly determined by particles in the size range of 50–500 nm that also contribute to PM<sub>2.5</sub> mass concentration.</p>

New Particle Formation Occurrence in the Urban Atmosphere of Beijing During 2013–2020

“…This finding is consistent with the study conducted in the boreal forest (Dada et al, 2017). The reason may be that when RH increases, the particle surface area will increase due to hygroscopic growth, thus restraining the level of NPF precursors (Cai et al, 2017). Also, the RH demonstrated a negative correlation with UVB, particularly during the summer (R = −0.66, p < 0.05), and to a lesser extent during the winter (R = −0.43, p < 0.05), spring (R = −0.33, p < 0.05), and fall (R = −0.17, p < 0.05).…”

“…A clear boundary around 0.01-0.03 s −1 was found in CS distributions (Figure 3g) between NPF and non-NPF days. Previous studies in the atmosphere of Beijing stated that aerosol surface area which correlated with CS is the decisive parameter (Cai et al, 2017). Similar to CS, NO X (Figure 3h) was markedly lower in NPF days, due to its restraining effects on the condensational particle growth by reducing the yields of HOMs in VOC oxidation (Yan et al, 2020).…”

“…The NPF frequency (NPF-freq) varied between 5% and 80% globally (Nieminen et al, 2018). The level of SA was not higher during days with NPF events ("NPF days" hereinafter) compared with days without NPF events (non-NPF days) (Yan et al, 2021), and the level of the condensational sink (CS) or particle surface area is the critical parameter to separate the NPF and non-NPF days (Cai et al, 2017;Deng et al, 2020). The ratio between particle growth rate and CS was proposed to indicate the survival probability of nucleated clusters under coagulation, as well as the NPF occurrence (Kuang et al, 2010;Kulmala et al, 2017;McMurry et al, 2005).…”