Evaluation on the role of sulfuric acid in the mechanisms of new particle formation for Beijing case

103

Abstract. The predominating role of aerosol Fuchs surface area, A Fuchs , in determining the occurrence of new particle formation (NPF) events in Beijing was elucidated in this study. The analysis was based on a field campaign from 12 March to 6 April 2016 in Beijing, during which aerosol size distributions down to ∼ 1 nm and sulfuric acid concentrations were simultaneously monitored. The 26 days were classified into 11 typical NPF days, 2 undefined days, and 13 non-event days. A dimensionless factor, L , characterized by the relative ratio of the coagulation scavenging rate over the condensational growth rate (Kuang et al., 2010), was applied in this work to reveal the governing factors for NPF events in Beijing. The three parameters determining L are sulfuric acid concentration, the growth enhancement factor characterized by contribution of other gaseous precursors to particle growth, , and A Fuchs . Different from other atmospheric environments, such as in Boulder and Hyytiälä, the dailymaximum sulfuric acid concentration and in Beijing varied in a narrow range with geometric standard deviations of 1.40 and 1.31, respectively. A positive correlation between the estimated new particle formation rate, J 1.5 , and sulfuric acid concentration was found with a mean fitted exponent of 2.4. However, the maximum sulfuric acid concentrations on NPF days were not significantly higher (even lower, sometimes) than those on non-event days, indicating that the abundance of sulfuric acid in Beijing was high enough to initiate nucleation, but may not necessarily lead to NPF events. Instead, A Fuchs in Beijing varied greatly among days with a geometric standard deviation of 2.56, whereas the variabilities of A Fuchs in Tecamac, Atlanta, and Boulder were reported to be much smaller. In addition, there was a good correlation between A Fuchs and L in Beijing (R 2 = 0.88). Therefore, it was A Fuchs that fundamentally determined the occurrence of NPF events. Among 11 observed NPF events, 10 events occurred when A Fuchs was smaller than 200 µm 2 cm −3 . NPF events were suppressed due to the coagulation scavenging when A Fuchs was greater than 200 µm 2 cm −3 . Measured A Fuchs in Beijing had a good correlation with its PM 2.5 mass concentration (R 2 = 0.85) since A Fuchs in Beijing was mainly determined by particles in the size range of 50-500 nm that also contribute to the PM 2.5 mass concentration.

Section: Methodssupporting

confidence: 51%

Aerosol surface area concentration: a governing factor in new particle formation in Beijing

Cai¹,

Yang²,

Fu³

et al. 2017

103

“…A and K refer to the activation and kinetic nucleation coefficients, respectively, with values of 3.0 × 10 −6 s −1 and 8.0 × 10 −13 cm 3 s −1 . These values are close to the measured median values of 17 NPF event days during CAREBeijing 2008 (Wang et al, 2013b), however, several times higher compared to the results derived from other field measurements and model simulations in clean environments (Boy et al, 2008a;Paasonen et al, 2010;Riipinen et al, 2007;Wang et al, 2011). Recent research results indicate that sulfuric acid is not the only compound taking part in new particle formation, but low-volatile organic vapours are also needed Lauros et al, 2011;Metzger et al, 2010;Riipinen et al, 2012).…”

Section: Aerosolsupporting

confidence: 49%

The simulations of sulfuric acid concentration and new particle formation in an urban atmosphere in China

Wang

Mogensen

et al. 2013

Self Cite

Abstract. Simulations of sulfuric acid concentration and new particle formation are performed by using the zerodimensional version of the model MALTE (Model to predict new Aerosol formation in the Lower TropospherE) and measurements from the Campaign of Air Quality Research in Beijing and Surrounding areas (CAREBeijing) in 2008. Chemical reactions from the Master Chemical Mechanism version 3.2 (MCM v3.2) are used in the model. High correlation (slope = 0.72, R = 0.74) between the modelled and observed sulfuric acid concentrations is found during daytime (06:00-18:00). The aerosol dynamics are simulated by the University of Helsinki Multicomponent Aerosol (UHMA) model including several nucleation mechanisms. The results indicate that the model is able to predict the on-and offset of new particle formation in an urban atmosphere in China. In addition, the number concentrations of newly formed particles in kinetic-type nucleation including homogenous homomolecular (J = K[H 2 SO 4 ] 2 ) and homogenous heteromolecular nucleation involving organic vapours (J = K het [H 2 SO 4 ][Org]) are in satisfactory agreement with the observations. However, the specific organic compounds that possibly participate in the nucleation process should be investigated in further studies. For the particle growth, only a small fraction of the oxidized total organics condense onto the particles in polluted environments. Meanwhile, the OH and O 3 oxidation mechanism contribute 5.5 % and 94.5 % to the volume concentration of small particles, indicating the particle growth is more controlled by the precursor gases and their oxidation by O 3 .

“…The upper bound, d u , is selected as 6 nm is some recent studies (Sihto et al, 2006;Riipinen et al, 2007;Paasonen et al, 2009;Wang et al, 2011;Vuollekoski et al, 2012; as shown in Eq. (8).…”

Section: Previous Formulae For Comparisonmentioning

confidence: 99%

“…Kulmala et al (2004) recommended the upper size bound as the maximum size that the critical cluster can reach during a short time interval of growth. There are also studies using narrower size ranges, such as from 3 to 6 nm (Sihto et al, 2006;Paasonen et al, 2009;Wang et al, 2011;Vuollekoski et al, 2012) and from 1.34 to 3 nm (Xiao et al, 2015). In principle, the estimated formation rates may vary when different particle size ranges are used.…”

Section: Introductionmentioning

confidence: 99%

A new balance formula to estimate new particle formation rate: reevaluating the effect of coagulation scavenging

Cai

Jiang

2017

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.