Coagulation Sink Research Articles

Atmospheric Cluster Dynamics Code: a flexible method for solution of the birth-death equations

Abstract. The Atmospheric Cluster Dynamics Code (ACDC) is presented and explored. This program was created to study the first steps of atmospheric new particle formation by examining the formation of molecular clusters from atmospherically relevant molecules. The program models the cluster kinetics by explicit solution of the birth–death equations, using an efficient computer script for their generation and the MATLAB ode15s routine for their solution. Through the use of evaporation rate coefficients derived from formation free energies calculated by quantum chemical methods for clusters containing dimethylamine or ammonia and sulphuric acid, we have explored the effect of changing various parameters at atmospherically relevant monomer concentrations. We have included in our model clusters with 0–4 base molecules and 0–4 sulfuric acid molecules for which we have commensurable quantum chemical data. The tests demonstrate that large effects can be seen for even small changes in different parameters, due to the non-linearity of the system. In particular, changing the temperature had a significant impact on the steady-state concentrations of all clusters, while the boundary effects (allowing clusters to grow to sizes beyond the largest cluster that the code keeps track of, or forbidding such processes), coagulation sink terms, non-monomer collisions, sticking probabilities and monomer concentrations did not show as large effects under the conditions studied. Removal of coagulation sink terms prevented the system from reaching the steady state when all the initial cluster concentrations were set to the default value of 1 m−3, which is probably an effect caused by studying only relatively small cluster sizes.

Estimating the direct and indirect effects of secondary organic aerosols using ECHAM5-HAM

Abstract. Secondary organic aerosol (SOA) has been introduced into the global climate-aerosol model ECHAM5/HAM. The SOA module handles aerosols originating from both biogenic and anthropogenic sources. The model simulates the emission of precursor gases, their chemical conversion into condensable gases, the partitioning of semi-volatile condenable species into the gas and aerosol phases. As ECHAM5/HAM is a size-resolved model, a new method that permits the calculation of partitioning of semi-volatile species between different size classes is introduced. We compare results of modelled organic aerosol concentrations against measurements from extensive measurement networks in Europe and the United States, running the model with and without SOA. We also compare modelled aerosol optical depth against measurements from the AERONET network of grond stations. We find that SOA improves agreement between model and measurements in both organic aerosol mass and aerosol optical depth, but does not fully correct the low bias that is present in the model for both of these quantities. Although many models now include SOA, any overall estimate of the direct and indirect effects of these aerosols is still lacking. This paper makes a first step in that direction. The model is applied to estimate the direct and indirect effects of SOA under simulated year 2000 conditions. The modelled SOA spatial distribution indicates that SOA is likely to be an important source of free and upper tropospheric aerosol. We find a negative shortwave (SW) forcing from the direct effect, amounting to −0.31 Wm−2 on the global annual mean. In contrast, the model indicates a positive indirect effect of SOA of +0.23 Wm−2, arising from the enlargement of particles due to condensation of SOA, together with an enhanced coagulation sink of small particles. In the longwave, model results are a direct effect of +0.02 Wm−2 and an indirect effect of −0.03 Wm−2.

Physical characterization of aerosol particles during the Chinese New Year’s firework events

Abstract Measurements for particles 10 nm to 10 μm were taken using a Wide-range Particle Spectrometer during the Chinese New Year (CNY) celebrations in 2009 in Shanghai, China. These celebrations provided an opportunity to study the number concentration and size distribution of particles in an especial atmospheric pollution situation due to firework displays. The firework activities had a clear contribution to the number concentration of small accumulation mode particles (100–500 nm) and PM1 mass concentration, with a maximum total number concentration of 3.8 × 104 cm−3. A clear shift of particles from nucleation and Aitken mode to small accumulation mode was observed at the peak of the CNY firework event, which can be explained by reduced atmospheric lifetimes of smaller particles via the concept of the coagulation sink. High particle density (2.7 g cm−3) was identified as being particularly characteristic of the firework aerosols. Recalculated fine particles PM1 exhibited on average above 150 μg m−3 for more than 12 hours, which was a health risk to susceptible individuals. Integral physical parameters of firework aerosols were calculated for understanding their physical properties and further model simulation.

Competition of coagulation sink and source rate: New particle formation in the Pearl River Delta of China

The coagulation sink and its role in new particle formation are investigated based on data obtained during the PRIDE-PRD2004 campaign at Xinken of Pearl River Delta, China. Analysis of size distributions and mode contributions of the coagulation sink show that the observed higher load of accumulation mode particles impose a significant effect on the coagulation sink and result in higher coagulation sinks at Xinken despite of the lower total particle number compared with other areas. Hence it is concluded that the higher coagulation sink may depress the occurrence frequency of new particle formation events. The strategies targeting at controlling accumulation mode particles may have influences on the frequency of new particle formation events at this area. The factors affecting the coagulation sink are evaluated. The relatively lower ambient relative humidities may weaken the coagulation sink and facilitate the occurrence of new particle formation events during noontime, while the surmise of nucleation and growth involving organic matter may imply an actually higher coagulation sink than expected. These factors have a significant influence on the ultimate fate of the newly formed nuclei and new particle formation. A comparison of event and non-event days indicates that the coagulation sink is not the only decisive factor affecting new particle formation, other factors including the precursor vapors and photochemical activity are none the less important either. Competition of coagulation sink and high source rate leads to the occurrence of new particle formation events at Xinken.

Impact of krypton-85 beta radiation on aerosol particle formation and transformation

In this study the effect of the air ionization by 85 Kr beta radiation on the new particle formation and evolution of aerosol particle size distribution in the experimental chamber was investigated. During the experiments the interaction between air ionization and gas-to-particle conversion processes was distinctly observed. Results showed that the amplitude of the ionic current was dependent both on the chemical impurity concentration and the ionization source activity. Calculated values of parameters (growth and formation rates) of the particle nucleation process were larger when in the experimental chamber concentrations of SO2 and 85 Kr were higher. The growth rate values (42.1 and 45.3 nm=h) were by one order of magnitude higher than the environmental ones (1.2n9.9 nm=h at the Preila station, Lithuania). Experimental data showed that after injection of high SO2 and 85 Kr concentrations in the chamber during the 20 min interval nanometre-size particles created by nucleation were produced in large amounts. Thus, a larger amount of SO2 signicantly inuenced the formation of new particles. During the rst 5 min the concentration of 10 nm particles increased by 3 orders of magnitude with the formation rate of 7.47 cm i3 s i1 . The formation rate of 0.06 cm i3 s i1 in the experiment with the average ambient SO2 concentration (2n3 „g=m 3 ) was analogous to the environmental one (0.14 cm i3 s i1 ). The coagulation sink (CoagS 1;2;3 ) was higher in the experiment with the ambient SO2 concentration and resulted in the lower concentration of particles. The smaller values of the coagulation sink at the higher concentration of SO2 gas have shown that these nano-particles in the air could persist for a longer time, probably in a stable size due to the ion charge.

Suppression of nucleation mode particles by biomass burning in an urban environment: a case study

Measurements of concentrations and size distributions of particles 4.7 to 160 nm were taken using an SMPS during the bonfire and firework celebrations on Bonfire Night in Leeds, UK, 2006. These celebrations provided an opportunity to study size distributions in a unique atmospheric pollution situation during and following a significant emission event due to open biomass burning. A log-normal fitting program was used to determine the characteristics of the modal groups present within hourly averaged size distributions. Results from the modal fitting showed that on bonfire night the smallest nucleation mode, which was present before and after the bonfire event and on comparison weekends, was not detected within the size distribution. In addition, there was a significant shift in the modal diameters of the remaining modes during the peak of the pollution event. Using the concept of a coagulation sink, the atmospheric lifetimes of smaller particles were significantly reduced during the pollution event, and thus were used to explain the disappearance of the smallest nucleation mode as well as changes in particle count mean diameters. The significance for particle mixing state is discussed.

Estimating nucleation rates from apparent particle formation rates and vice versa: Revised formulation of the Kerminen–Kulmala equation

Connections between observed particle formation rates (typically at diameter 3 nm or larger) and the actual nucleation rates have important applications in atmospheric science. First, nucleation theories can be evaluated and second, semi-empirical particle formation rates can be developed for large scale models that neglect the cumbersome initial steps of formation and growth. Kerminen and Kulmala, by estimating the particle formation rate, nucleation mode growth rate and scavenging rate onto background particles (coagulation sink) from measured size distribution evolution, derived a simple yet rather accurate formula for this purpose [Kerminen V.-M., Kulmala, M. (2002). Analytical formulae connecting the “real” and the “apparent” 25 nucleation rate and the nuclei number concentration for atmospheric nucleation events, Journal of Aerosol Science 33, 609–622]. The present work reformulates the original theory in a way that two drawbacks are eliminated: (1) the original expression was derived using a slightly inaccurate coagulation sink dependence on particle size and (2) was based on knowing the condensation sink which requires knowledge of the condensing vapors.

Relationship and variations of aerosol number and PM10 mass concentrations in a highly polluted urban environment?New Delhi, India

Abstract Measurements of the aerosol number concentration and the PM 10 mass concentrations of urban background aerosols in different seasons were performed in New Delhi 2002, including the simultaneous measurements of NO 2 , SO 2 and CO concentrations. The results indicate an interesting relationship between the aerosol number and the PM 10 mass concentrations. The number concentration increases with the mass concentration up to 300 μg m −3 . However, after this point, the number concentration decreases even if the mass concentration increases. An explanation for this nonlinear behavior is proposed through a dynamic model involving the coagulation sink concept. The linear relationship between the mass and the number concentration in ambient air is valid if the mass concentration is relatively low. A high sink, however, means that the number concentration cannot be high—resulting in a decline in the number vs. mass plot. Clear diurnal, weekly and seasonal variations in concentrations were observed. High number concentrations of aerosols were observed in the mornings (7–8 a.m.) and in the evenings (7–10 p.m.). The number concentration was highest in March and lowest in June and the mass concentration was highest in November and lowest in June. The number concentration was higher during weekdays, but the mass concentration was higher during weekends. The number concentration correlates with the NO 2 concentration, which indicates that one major source of aerosol particles for the monitored site in New Delhi may be vehicular emission, but also domestic use of fossil fuels and biofuels cannot be neglected.

Condensation and coagulation sinks and formation of nucleation mode particles in coastal and boreal forest boundary layers

The formation and growth of new particles has been evaluated using a revised version of a simple, but novel, theoretical tool. The concentration of condensable vapors and their source rates has been estimated using the aerosol condensation sink together with the measured particle growth rate. Also, by adding the coagulation sink and the measured formation rate of 3 nm particles, the formation rate of 1 nm particles and their concentration can be estimated. Condensation and coagulation sinks can be obtained from ambient aerosol size distribution data. The method has been applied to analyze the particle formation and growth rates observed during coastal and boreal forest nucleation events. The condensation sinks are typically 4–7 × 10−3 s−1 in the forest and 2 × 10−3 s−1 under coastal conditions, while the coagulation sinks for 1, 2, and 3 nm particles are typically smaller by factors 1.5–2, 5–7, and 11–15, respectively. The measured growth rates are 2–10 nm/h for the boreal forest and range from 15 to 180 nm/h at the coast, corresponding to a vapor concentration of 2–13 × 107 cm−3 and 108 cm−3 to 109 cm−3, respectively. The vapor source rate was 1–2 × 105 cm−3s−1 in the boreal forest and 2–5 × 106 cm−3s−1 in the coastal environment. The estimated formation rate of 1 nm particles in the forest environment was 8–20 cm−3s−1 and 300–10,000 cm−3s−1 at the coast. The concentration of 1 nm particles was estimated to be 2000–5000 and 4 × 104–7 × 106 particles cm−3 in forest and at coast, respectively.

On the formation, growth and composition of nucleation mode particles

Taking advantage of only the measured aerosol particles spectral evolution as a function of time, a new analytical tool is developed to derive formation and growth properties of nucleation mode aerosols. This method, when used with hygroscopic growth-factors, can also estimate basic composition properties of these recently-formed particles. From size spectra the diameter growth-rate can be obtained, and aerosol condensation and coagulation sinks can be calculated. Using this growth-rate and condensation sink, the concentration of condensable vapours and their source rate can be estimated. Then, combining the coagulation sink together with measured number concentrations and apparent source rates of 3 nm particles, 1 nm particle nucleation rates and concentration can be estimated. To estimate nucleation rates and vapour concentration source rates producing new particle bursts over the Boreal forest regions, three cases from the BIOFOR project were examined using this analytical tool. In this environment, the nucleation mode growth-rate was observed to be 2–3 nm hour−1, which required a condensable vapour concentration of 2.5–4×107 cm−3 and a source rate of approximately 7.5–11×104 cm−3 s−1 to be sustained. The formation rate of 3 nm particles was =1 particle cm−3 s−1 in all three cases. The estimated formation rate of 1 nm particles was 10–100 particles cm−3 s−1, while their concentration was estimated to be between 10,000 and 100,000 particles cm−3. Using hygroscopicity data and mass flux expressions, the mass flux of insoluble vapour is estimated to be of the same order of magnitude as that of soluble vapour, with a soluble to insoluble vapour flux ratio ranging from 0.7 to 1.4 during these nucleation events.

On the formation, growth and composition of nucleation mode particles

Taking advantage of only the measured aerosol particles spectral evolution as a function of time, a new analytical tool is developed to derive formation and growth properties of nucleation mode aerosols. This method, when used with hygroscopic growth-factors, can also estimate basic composition properties of these recently-formed particles. From size spectra the diameter growth-rate can be obtained, and aerosol condensation and coagulation sinks can be calculated. Using this growth-rate and condensation sink, the concentration of condensable vapours and their source rate can be estimated. Then, combining the coagulation sink together with measured number concentrations and apparent source rates of 3 nm particles, 1 nm particle nucleation rates and concentration can be estimated. To estimate nucleation rates and vapour concentration source rates producing new particle bursts over the Boreal forest regions, three cases from the BIOFOR project were examined using this analytical tool. In this environment, the nucleation mode growth-rate was observed to be 2–3 nm hour−1, which required a condensable vapour concentration of 2.5–4×107 cm−3 and a source rate of approximately 7.5–11×104 cm−3 s−1 to be sustained. The formation rate of 3 nm particles was =1 particle cm−3 s−1 in all three cases. The estimated formation rate of 1 nm particles was 10–100 particles cm−3 s−1, while their concentration was estimated to be between 10,000 and 100,000 particles cm−3. Using hygroscopicity data and mass flux expressions, the mass flux of insoluble vapour is estimated to be of the same order of magnitude as that of soluble vapour, with a soluble to insoluble vapour flux ratio ranging from 0.7 to 1.4 during these nucleation events.