scholarly journals New particle formation in the sulfuric acid–dimethylamine–water system: reevaluation of CLOUD chamber measurements and comparison to an aerosol nucleation and growth model

2018 ◽  
Vol 18 (2) ◽  
pp. 845-863 ◽  
Author(s):  
Andreas Kürten ◽  
Chenxi Li ◽  
Federico Bianchi ◽  
Joachim Curtius ◽  
António Dias ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Detection Threshold ◽  
Sulfuric Acid Concentration ◽  
Water System ◽  
Particle Formation ◽  
New Particle Formation ◽  
Flow Tube ◽  
Aerosol Model ◽  
Wide Range ◽  
Good Agreement

Abstract. A recent CLOUD (Cosmics Leaving OUtdoor Droplets) chamber study showed that sulfuric acid and dimethylamine produce new aerosols very efficiently and yield particle formation rates that are compatible with boundary layer observations. These previously published new particle formation (NPF) rates are reanalyzed in the present study with an advanced method. The results show that the NPF rates at 1.7 nm are more than a factor of 10 faster than previously published due to earlier approximations in correcting particle measurements made at a larger detection threshold. The revised NPF rates agree almost perfectly with calculated rates from a kinetic aerosol model at different sizes (1.7 and 4.3 nm mobility diameter). In addition, modeled and measured size distributions show good agreement over a wide range of sizes (up to ca. 30 nm). Furthermore, the aerosol model is modified such that evaporation rates for some clusters can be taken into account; these evaporation rates were previously published from a flow tube study. Using this model, the findings from the present study and the flow tube experiment can be brought into good agreement for the high base-to-acid ratios (∼ 100) relevant for this study. This confirms that nucleation proceeds at rates that are compatible with collision-controlled (a.k.a. kinetically controlled) NPF for the conditions during the CLOUD7 experiment (278 K, 38 % relative humidity, sulfuric acid concentration between 1 × 106 and 3 × 107 cm−3, and dimethylamine mixing ratio of ∼ 40 pptv, i.e., 1 × 109 cm−3).

scholarly journals New particle formation in the sulfuric acid-dimethy lamine-water system: Reevaluation of CLOUD chamber measurements and comparison to an aerosol nucleation and growth model

2017 ◽  
Author(s):  
Andreas Kürten ◽  
Chenxi Li ◽  
Federico Bianchi ◽  
Joachim Curtius ◽  
António Dias ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sulfuric Acid ◽  
Detection Threshold ◽  
Sulfuric Acid Concentration ◽  
Particle Formation ◽  
New Particle Formation ◽  
Flow Tube ◽  
Aerosol Model ◽  
Wide Range ◽  
Good Agreement

Abstract. A recent CLOUD (Cosmics Leaving OUtdoor Droplets) chamber study showed that sulfuric acid and dimethylamine produce new aerosols very efficiently, and yield particle formation rates that are compatible with boundary layer observations. These previously published new particle formation (NPF) rates are re-analyzed in the present study with an advanced method. The results show that the NPF rates at 1.7 nm are more than a factor of 10 faster than previously published due to earlier approximations in correcting particle measurements made at larger detection threshold. The revised NPF rates agree almost perfectly with calculated rates from a kinetic aerosol model at different sizes (1.7 nm and 4.3 nm mobility diameter). In addition, modeled and measured size distributions show good agreement over a wide range (up to ca. 30 nm). Furthermore, the aerosol model is modified such that evaporation rates for some clusters can be taken into account; these evaporation rates were previously published from a flow tube study. Using this model, the findings from the present study and the flow tube experiment can be brought into good agreement. This confirms that nucleation proceeds at rates that are compatible with collision-controlled (a.k.a. kinetically-controlled) new particle formation for the conditions during the CLOUD7 experiment (278 K, 38 % RH, sulfuric acid concentration between 1 × 106 and 3 × 107 cm−3 and dimethylamine mixing ratio of ~ 40 pptv). Finally, the simulation of atmospheric new particle formation reveals that even tiny mixing ratios of dimethylamine (0.1 pptv) yield NPF rates that could explain significant boundary layer particle formation. This highlights the need for improved speciation and quantification techniques for atmospheric gas-phase amine measurements.

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

2017 ◽  
Author(s):  
Runlong Cai ◽  
Dongsen Yang ◽  
Yueyun Fu ◽  
Xing Wang ◽  
Xiaoxiao Li ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Surface Area ◽  
Acid Concentration ◽  
Mass Concentration ◽  
Sulfuric Acid Concentration ◽  
Particle Formation ◽  
Atmospheric Environment ◽  
Geometric Standard Deviation ◽  
Growth Enhancement ◽  
New Particle Formation

Abstract. The predominating role of aerosol Fuchs surface area, AFuchs, 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 12th to April 6th, 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, LΓ, 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 LΓ are sulfuric acid concentration, the growth enhancement factor characterizing contribution of other gaseous precursors to particle growth, Γ, and AFuchs. 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, J1.5, 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, AFuchs 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 AFuchs and LΓ in Beijing (R2 = 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 AFuchs that determines the occurrence of NPF event in Beijing. 10 in 11 NPF events occurred when AFuchs is smaller than 200 μm2/cm3, and the NPF event was suppressed due to coagulation scavenging when AFuchs is larger than 200 μm2/cm3. Measured AFuchs is in good correlation with PM2.5 mass concentration (R2 = 0.85) since AFuchs in Beijing is mainly determined by particles in the size range of 50–500 nm that also contribute to PM2.5 mass concentration.

Improved identification of evaporation rates and thermodynamic data by Monte-Carlo method

2020 ◽  
Author(s):  
Anna Shcherbacheva ◽  
Tapio Helin ◽  
Heikki Haario ◽  
Hanna Vehkamäki
Keyword(s):  
Monte Carlo ◽  
Sulfuric Acid ◽  
Thermodynamic Data ◽  
Particle Formation ◽  
Forward Problem ◽  
Dependent Data ◽  
New Particle Formation ◽  
Free Energies ◽  
Wide Range ◽  
Cluster Composition

<p>Atmospheric new particle formation and successive cluster growth to aerosol particles is an important field of research, in particular due to climate change phenomena and air quality monitoring. Recent developments in the instrumentation have enabled quantification of ionic clusters formed in the gas phase at the first steps of particle formation under atmospherically relevant mixing ratios. However, electrically neutral clusters are prevalent in atmospheric conditions, and thus must be charged prior to detection by mass spectrometer. The charging process can lead to cluster fragmentation and thus alter the measured cluster composition.</p><p>Even when the cluster composition can be measured directly, this does not quantify individual cluster-level properties, such as cluster collision and evaporation rates. Collision rates contain relatively small uncertainties in comparison to evaporation rates, which are computed using detailed balance assumption together with the free energies of cluster formation, which can in turn be obtained from Quantum chemistry (QC) methods. As evaporation rates depend exponentially on the free energies, even difference by several kcal/mol between different QC methods results in orders of magnitude differences in evaporation rates.</p><p>On the other hand, in spite of the error margins associated with the evaporation rates, simulations of cluster populations, which incorporate collision and evaporation rates as free parameters (such as Becker-Döring models), have demonstrated good qualitative agreement with experimental data. The Becker-Döring equations are a system of Ordinary Differential equations (ODE) which account for cluster birth and death processes, as well as external sinks and sources. In mathematical terms, prediction of cluster concentrations using kinetic simulations with given cluster collision and evaporation rates is called a forward problem.</p><p>In the present study, we focus on the so-called inverse problem of how to derive the evaporation rates and thermodynamic data (enthalpy change and entropy change due to addition or removal of molecule) from available measurements, rather than on the forward problem. We do this by Delayed Rejection Adaptive Monte Carlo (DRAM) method for the system containing sulfuric acid and ammonia with the maximal size of the pentamer. Initially, we tested the method on the synthetic data created from Atmospheric Cluster Dynamic Code (ACDC) simulations. By so doing, we identify the combination of fitted parameters and concentration measurements, which leads to the best identification of the evaporation rates. Additionally, we demonstrated that the temperature-dependent data yield better estimates of the evaporation rates as compared to the time-dependent data measured before the system has reached the steady state.</p><p>Next, we apply the technique to improve the identification of the evaporation rates from CLOUD chamber data, which contain cluster concentrations and new particle formation rates measured at different temperatures and a wide range of atmospherically relevant sulfuric acid and ammonia concentrations. As a result, we were able to obtain the probability density functions (PDFs) that show small standard variations for thermodynamic data. By using the values from the PDFs as parameters in the ACDC model, we achieve a fair agreement with the measured NPFs and cluster concentrations for a wide range of temperatures.</p>

scholarly journals New particle formation from sulfuric acid and ammonia: nucleation and growth model based on thermodynamics derived from CLOUD measurements for a wide range of conditions

2019 ◽  
Author(s):  
Andreas Kürten
Keyword(s):  
Sulfuric Acid ◽  
Growth Model ◽  
Thermodynamic Data ◽  
Particle Formation ◽  
Nucleation And Growth ◽  
Aerosol Size Distribution ◽  
Formation Mechanisms ◽  
Strong Impact ◽  
New Particle Formation ◽  
Wide Range

Abstract. Understanding new particle formation and growth is important because of the strong impact of these processes on climate and air quality. Measurements to elucidate the main new particle formation mechanisms are essential; however, these mechanisms have to be implemented in models to estimate their impact on the regional and global scale. Parameterizations are computationally cheap ways of implementing nucleation schemes in models but they have their limitations, as they do not necessarily include all relevant parameters. Process models using sophisticated nucleation schemes can be useful for the generation of look-up tables in large-scale models or for the analysis of individual new particle formation events. In addition, some other important properties can be derived from a process model that implicitly calculates the evolution of the full aerosol size distribution, e.g., the particle growth rates. Within this study, a model (SANTIAGO, Sulfuric acid Ammonia NucleaTIon And GrOwth model) is constructed that simulates new particle formation starting from the monomer of sulfuric acid up to a particle size of several hundred nanometers. The smallest sulfuric acid clusters containing one to four acid molecules and varying amount of base (ammonia) are allowed to evaporate in the model, whereas growth beyond the pentamer (5 sulfuric acid molecules) is assumed to be entirely collision-controlled. The main goal of the present study is to derive appropriate thermodynamic data needed to calculate the cluster evaporation rates as a function of temperature. These data are derived numerically from CLOUD (Cosmics Leaving OUtdoor Droplets) chamber new particle formation rates for neutral sulfuric acid-water-ammonia nucleation at temperatures between 208 K and 292 K. The numeric methods include an optimization scheme to derive the best estimates for the thermodynamic data (dH and dS) and a Monte Carlo method to derive their probability density functions. The derived data are compared to literature values. Using different data sets for dH and dS in SANTIAGO detailed comparison between model results and measured CLOUD new particle formation rates is discussed.

scholarly journals New particle formation from sulfuric acid and ammonia: nucleation and growth model based on thermodynamics derived from CLOUD measurements for a wide range of conditions

2019 ◽  
Vol 19 (7) ◽  
pp. 5033-5050 ◽  
Author(s):  
Andreas Kürten
Keyword(s):  
Sulfuric Acid ◽  
Growth Model ◽  
Thermodynamic Data ◽  
Particle Formation ◽  
Nucleation And Growth ◽  
Aerosol Size Distribution ◽  
Formation Mechanisms ◽  
Strong Impact ◽  
New Particle Formation ◽  
Wide Range

Abstract. Understanding new particle formation and growth is important because of the strong impact of these processes on climate and air quality. Measurements to elucidate the main new particle formation mechanisms are essential; however, these mechanisms have to be implemented in models to estimate their impact on the regional and global scale. Parameterizations are computationally cheap ways of implementing nucleation schemes in models, but they have their limitations, as they do not necessarily include all relevant parameters. Process models using sophisticated nucleation schemes can be useful for the generation of look-up tables in large-scale models or for the analysis of individual new particle formation events. In addition, some other important properties can be derived from a process model that implicitly calculates the evolution of the full aerosol size distribution, e.g., the particle growth rates. Within this study, a model (SANTIAGO – Sulfuric acid Ammonia NucleaTIon And GrOwth model) is constructed that simulates new particle formation starting from the monomer of sulfuric acid up to a particle size of several hundred nanometers. The smallest sulfuric acid clusters containing one to four acid molecules and a varying amount of base (ammonia) are allowed to evaporate in the model, whereas growth beyond the pentamer (five sulfuric acid molecules) is assumed to be entirely collision-controlled. The main goal of the present study is to derive appropriate thermodynamic data needed to calculate the cluster evaporation rates as a function of temperature. These data are derived numerically from CLOUD (Cosmics Leaving OUtdoor Droplets) chamber new particle formation rates for neutral sulfuric acid–water–ammonia nucleation at temperatures between 208 and 292 K. The numeric methods include an optimization scheme to derive the best estimates for the thermodynamic data (dH and dS) and a Monte Carlo method to derive their probability density functions. The derived data are compared to literature values. Using different data sets for dH and dS in SANTIAGO detailed comparison between model results and measured CLOUD new particle formation rates is discussed.

scholarly journals On the composition of ammonia-sulfuric acid clusters during aerosol particle formation

2014 ◽  
Vol 14 (9) ◽  
pp. 13413-13464 ◽  
Author(s):  
S. Schobesberger ◽  
A. Franchin ◽  
F. Bianchi ◽  
L. Rondo ◽  
J. Duplissy ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sulfuric Acid ◽  
Gas Phase ◽  
Particle Formation ◽  
Atmospheric Conditions ◽  
New Particle Formation ◽  
Acid Base ◽  
Wide Range ◽  
Charged Clusters ◽  
Positively Charged

Abstract. The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD) facility at CERN tries to elucidate which vapors are responsible for this new particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH3) and sulfuric acid (H2SO4). Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH3-H2SO4 clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH3] in the range from <2 to 1400 pptv, [H2SO4] from 3.3 × 106 to 1.4 × 109 cm−3, and a temperature range from −25 to +20 °C. Negatively and positively charged clusters were directly measured by an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer, as they initially formed from gas-phase NH3 and H2SO4, and then grew to larger clusters containing more than 50 molecules of NH3 and H2SO4, corresponding to mobility-equivalent diameters greater than 2 nm. Water molecules evaporate from these clusters during sampling and are not observed. We found that the composition of the NH3-H2SO4 clusters is primarily determined by the ratio of gas-phase concentrations [NH3] / [H2SO4], as well as by temperature. Pure binary H2O-H2SO4 clusters (observed as clusters of only H2SO4) only form at [NH3] / [H2SO4]<0.1 to 1. For larger values of [NH3] / [H2SO4], the composition of NH3-H2SO4 clusters was characterized by the number of NH3 molecules m added for each added H2SO4 molecule n (Δm / Δn), where n is in the range 4–18 (negatively charged clusters) or 1–17 (positively charged clusters). For negatively charged clusters, Δm / Δn saturated between 1 and 1.4 for [NH3] / [H2SO4]>10. Positively charged clusters grew on average by Δm / Δn = 1.05 and were only observed at sufficiently high [NH3] / [H2SO4]. The H2SO4 molecules of these clusters are partially neutralized by NH3, in close resemblance to the acid-base bindings of ammonium bisulfate. Supported by model simulations, we substantiate previous evidence for acid-base reactions being the essential mechanism behind the formation of these clusters under atmospheric conditions and up to sizes of at least 2 nm. Our results also suggest that yet unobservable electrically neutral NH3-H2SO4 clusters grow by generally the same mechanism as ionic clusters, particularly for [NH3] / [H2SO4]>10. We expect that NH3-H2SO4 clusters form and grow also mostly by Δm / Δn>1 in the atmosphere's boundary layer, as [NH3] / [H2SO4] is mostly larger than 10. We compared our results from CLOUD with APi-TOF measurements of NH3-H2SO4 anion clusters during new particle formation in the Finnish boreal forest. However, the exact role of NH3-H2SO4 clusters in boundary layer particle formation remains to be resolved.

scholarly journals Molecular insights into new particle formation in Barcelona, Spain

2020 ◽  
Vol 20 (16) ◽  
pp. 10029-10045 ◽  
Author(s):  
James Brean ◽  
David C. S. Beddows ◽  
Zongbo Shi ◽  
Brice Temime-Roussel ◽  
Nicolas Marchand ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Organic Compounds ◽  
Radiative Forcing ◽  
Cloud Condensation Nuclei ◽  
Sulfuric Acid Concentration ◽  
Particle Growth ◽  
Particle Formation ◽  
Necessary Condition ◽  
New Particle Formation ◽  
High Concentrations

Abstract. Atmospheric aerosols contribute some of the greatest uncertainties to estimates of global radiative forcing and have significant effects on human health. New particle formation (NPF) is the process by which new aerosols of sub-2 nm diameter form from gas-phase precursors and contributes significantly to particle numbers in the atmosphere, accounting for approximately 50 % of cloud condensation nuclei globally. Here, we study summertime NPF in urban Barcelona in north-eastern Spain utilising particle counting instruments down to 1.9 nm and a Nitrate Chemical Ionisation Atmospheric Pressure interface Time of Flight Mass Spectrometer (CI-APi-ToF). The rate of formation of new particles is seen to increase linearly with sulfuric acid concentration, although particle formation rates fall short of chamber studies of H2SO4–DMA–H2O while exceeding those of H2SO4–BioOxOrg–H2O nucleation, although a role of highly oxygenated molecules (HOMs) cannot be ruled out. The sulfuric acid dimer : monomer ratio is significantly lower than that seen in experiments involving sulfuric acid and dimethylamine (DMA) in chambers, indicating that stabilisation of sulfuric acid clusters by bases is weaker in this dataset than in chambers, either due to rapid evaporation due to high summertime temperatures or limited pools of stabilising amines. Such a mechanism cannot be verified in these data, as no higher-order H2SO4–amine clusters nor H2SO4–HOM clusters were measured. The high concentrations of HOMs arise from isoprene, alkylbenzene, monoterpene and polycyclic aromatic hydrocarbon (PAH) oxidation, with alkylbenzenes providing greater concentrations of HOMs due to significant local sources. The concentration of these HOMs shows a dependence on temperature. The organic compounds measured primarily fall into the semivolatile organic compound (SVOC) volatility class arising from alkylbenzene and isoprene oxidation. Low-volatility organic compounds (LVOCs) largely arise from oxidation of alkylbenzenes, PAHs and monoterpenes, whereas extremely low-volatility organic compounds (ELVOCs) arise from primarily PAH and monoterpene oxidation. New particle formation without growth past 10 nm is also observed, and on these days oxygenated organic concentrations are lower than on days with growth by a factor of 1.6, and thus high concentrations of low-volatility oxygenated organics which primarily derive from traffic-emitted volatile organic compounds (VOCs) appear to be a necessary condition for the growth of newly formed particles in Barcelona. These results are consistent with prior observations of new particle formation from sulfuric acid–amine reactions in both chambers and the real atmosphere and are likely representative of the urban background of many European Mediterranean cities. A role for HOMs in the nucleation process cannot be confirmed or ruled out, and there is strong circumstantial evidence of the participation of HOMs across multiple volatility classes in particle growth.

scholarly journals Effect of ions on the measurement of sulfuric acid in the CLOUD experiment at CERN

2014 ◽  
Vol 7 (11) ◽  
pp. 3849-3859 ◽  
Author(s):  
L. Rondo ◽  
A. Kürten ◽  
S. Ehrhart ◽  
S. Schobesberger ◽  
A. Franchin ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Mass Spectrometer ◽  
Acid Concentration ◽  
Uv Light ◽  
Sulfuric Acid Concentration ◽  
Particle Formation ◽  
Galactic Cosmic Rays ◽  
Cloud Chamber ◽  
Proton Synchrotron ◽  
New Particle Formation

Abstract. Ternary aerosol nucleation experiments were conducted in the CLOUD chamber at CERN in order to investigate the influence of ions on new particle formation. Neutral and ion-induced nucleation experiments, i.e. without and with the presence of ions, respectively, were carried out under precisely controlled conditions. The sulfuric acid concentration was measured with a chemical ionisation mass spectrometer (CIMS) during the new particle formation experiments. The added ternary trace gases were ammonia (NH3), dimethylamine (DMA, C2H7N) or oxidised products of pinanediol (PD, C10H18O2). When pinanediol was introduced into the chamber, an increase in the mass spectrometric signal used to determine the sulfuric acid concentration (m/z 97, i.e. HSO4−) was observed due to ions from the CLOUD chamber. The enhancement was only observed during ion-induced nucleation measurements by using either galactic cosmic rays (GCRs) or the proton synchrotron (PS) pion beam for the ion generation, respectively. The ion effect typically involved an increase in the apparent sulfuric acid concentration by a factor of ~ 2 to 3 and was qualitatively verified by the ion measurements with an atmospheric-pressure interface-time of flight (APi-TOF) mass spectrometer. By applying a high-voltage (HV) clearing field inside the CLOUD chamber, the ion effect on the CIMS measurement was completely eliminated since, under these conditions, small ions are swept from the chamber in about 1 s. In order to exclude the ion effect and to provide corrected sulfuric acid concentrations during the GCR and PS beam nucleation experiments, a parameterisation was derived that utilises the trace gas concentrations and the UV light intensity as input parameters. Atmospheric sulfuric acid measurements with a CIMS showed an insignificant ion effect.

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

2017 ◽  
Vol 17 (20) ◽  
pp. 12327-12340 ◽  
Author(s):  
Runlong Cai ◽  
Dongsen Yang ◽  
Yueyun Fu ◽  
Xing Wang ◽  
Xiaoxiao Li ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Surface Area ◽  
Acid Concentration ◽  
Mass Concentration ◽  
Sulfuric Acid Concentration ◽  
Particle Formation ◽  
Geometric Standard Deviation ◽  
Daily Maximum ◽  
Growth Enhancement ◽  
New Particle Formation

Abstract. The predominating role of aerosol Fuchs surface area, AFuchs, 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, LΓ, 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 LΓ are sulfuric acid concentration, the growth enhancement factor characterized by contribution of other gaseous precursors to particle growth, Γ, and AFuchs. Different from other atmospheric environments, such as in Boulder and Hyytiälä, the daily-maximum sulfuric acid concentration and Γ 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, J1.5, 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, AFuchs in Beijing varied greatly among days with a geometric standard deviation of 2.56, whereas the variabilities of AFuchs in Tecamac, Atlanta, and Boulder were reported to be much smaller. In addition, there was a good correlation between AFuchs and LΓ in Beijing (R2 = 0.88). Therefore, it was AFuchs that fundamentally determined the occurrence of NPF events. Among 11 observed NPF events, 10 events occurred when AFuchs was smaller than 200 µm2 cm−3. NPF events were suppressed due to the coagulation scavenging when AFuchs was greater than 200 µm2 cm−3. Measured AFuchs in Beijing had a good correlation with its PM2.5 mass concentration (R2 = 0.85) since AFuchs in Beijing was mainly determined by particles in the size range of 50–500 nm that also contribute to the PM2.5 mass concentration.

Sign in / Sign up

Export Citation Format

Share Document