Rate Of New Particle Formation Research Articles

Effect of Relative Humidity on the Rate of New Particle Formation for Different VOCs

Atmospheric new particle formation (NPF) is an important source of aerosol particles and cloud condensation nuclei, which affect both climate and human health. In pristine environments, oxidation of biogenic volatile organic compounds (VOCs) is a major contributor to NPF. However, the impact of relative humidity (RH) on NPF from these precursors remains poorly understood. Herein, we report on NPF, as inferred from measurements of total particle number density with a particle diameter (dp) > 7 nm, from three VOCs (sabinene, α-terpineol, and myrtenol) subjected to dark ozonolysis. From a series of comparative experiments under humid (60% RH) and dry (~0% RH) conditions and a variety of VOC mixing ratios (ξVOC, parts per billion by volume, ppbv), we show varied behavior in NPF at elevated RH depending on the VOC and ξVOC. In general, RH-dependent enhancement of NPF at an ξVOC between <1 ppbv and 20 ppbv was observed for select VOCs. Our results suggest that gaseous water at particle genesis enhances NPF by promoting the formation of low-volatility organic compound gas-phase products (LVOCs). This is supported by measurements of the rate of NPF for α-pinene-derived SOA, where RH had a greater influence on the initial rate of NPF than did ξVOC and ξO3.

Organosulfate produced from consumption of SO3 speeds up sulfuric acid–dimethylamine atmospheric nucleation

Abstract. Although sulfuric acid (SA) and dimethylamine (DMA)-driven nucleation mainly dominates the new particle formation (NPF) process in the atmosphere, seeking the involvement of other gaseous species remains crucial for a better understanding of the NPF. Organosulfate has been detected in the gas phase and abundantly in atmospheric fine particles. However, its molecular formation mechanism and its impact on the NPF are still much less understood. Here, we explored the gas-phase reaction of glycolic acid (GA) with SO3 and evaluated the enhancing potential of its products on the SA–DMA-driven NPF using a combination of quantum chemical calculations and kinetics modeling. We found that the considerable concentration of glycolic acid sulfate (GAS) is thermodynamically accessible from the reaction of GA with SO3, efficiently catalyzed by SA or H2O molecules. The produced GAS can form stable clusters with SA and DMA and speeds up the nucleation rate of the SA–DMA system obviously. Notably, the enhancement by GAS in the SA–DMA-based particle formation rate can be up to ∼ 800 times in the region where the concentration of SA is about 104 molec. cm−3. Supported by observations of atmospheric NPF events at Mt. Tai in China, our proposed ternary GAS–SA–DMA nucleation mechanism further indicates that the organosulfates produced from the consumption of SO3 may play an important role in the unexpected high NPF rates observed in areas with relatively low concentrations of SA. The presented reaction and nucleation mechanisms provide a new feasible source of organosulfates in atmospheric new particles. Based on our findings, the impact of organosulfates on the atmospheric NPF in multiple regions around the world was estimated and discussed.

Evidence of nitrate-based nighttime atmospheric nucleation driven by marine microorganisms in the South Pacific.

Our understanding of ocean-cloud interactions and their effect on climate lacks insight into a key pathway: do biogenic marine emissions form new particles in the open ocean atmosphere? Using measurements collected in ship-borne air-sea interface tanks deployed in the Southwestern Pacific Ocean, we identified new particle formation (NPF) during nighttime that was related to plankton community composition. We show that nitrate ions are the only species for which abundance could support NPF rates in our semicontrolled experiments. Nitrate ions also prevailed in the natural pristine marine atmosphere and were elevated under higher sub-10 nm particle concentrations. We hypothesize that these nucleation events were fueled by complex, short-term biogeochemical cycling involving the microbial loop. These findings suggest a new perspective with a previously unidentified role of nitrate of marine biogeochemical origin in aerosol nucleation.

Comprehensive simulations of new particle formation events in Beijing with a cluster dynamics–multicomponent sectional model

Abstract. New particle formation (NPF) and growth are a major source of atmospheric fine particles. In polluted urban environments, NPF events are frequently observed with characteristics distinct from those in clean environments. Here we simulate NPF events in urban Beijing with a discrete-sectional model that couples cluster dynamics and multicomponent particle growth. In the model, new particles are formed by sulfuric acid–dimethylamine nucleation, while particle growth is driven by particle coagulation and the condensation of sulfuric acid, its clusters, and oxygenated organic molecules (OOMs). A variable simulation domain in the particle size space is applied to isolate newly formed particles from preexisting ones, which allows us to focus on new particle formation and growth rather than the evolution of particles of non-NPF origin. The simulation yields a rich set of information including the time-dependent NPF rates, the cluster concentrations, the particle size distributions, and the time- and size-specific particle chemical compositions. These can be compared with the field observations to comprehensively assess the simulation–observation agreement. Sensitivity analysis with the model further quantifies how metrics of NPF events (e.g., particle survival probability) respond to model input variations and serves as a diagnostic tool to pinpoint the key parameter that leads to simulation–observation discrepancies. Seven typical NPF events in urban Beijing were analyzed. We found that with the observed gaseous precursor concentrations and coagulation sink as model inputs, the simulations roughly captured the evolution of the observed particle size distributions; however, the simulated particle growth rate was insufficient to yield the observed particle number concentrations, survival probability, and mode diameter. With the aid of sensitivity analysis, we identified under-detected OOMs as a likely cause for the discrepancy, and the agreement between the simulation and the observation was improved after we modulated particle growth rates in the simulation by adjusting the abundance of OOMs.

Atmospheric Sulfuric Acid-Multi-Base New Particle Formation Revealed through Quantum Chemistry Enhanced by Machine Learning.

The formation of molecular clusters and secondary aerosols in the atmosphere has a significant impact on the climate. Studies typically focus on the new particle formation (NPF) of sulfuric acid (SA) with a single base molecule (e.g., dimethylamine or ammonia). In this work, we examine the combinations and synergy of several bases. Specifically, we used computational quantum chemistry to perform configurational sampling (CS) of (SA)0-4(base)0-4 clusters with five different types of bases: ammonia (AM), methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), and ethylenediamine (EDA). Overall, we studied 316 different clusters. We used a traditional multilevel funnelling sampling approach augmented by a machine-learning (ML) step. The ML made the CS of these clusters possible by significantly enhancing the speed and quality of the search for the lowest free energy configurations. Subsequently, the cluster thermodynamics properties were evaluated at the DLPNO-CCSD(T0)/aug-cc-pVTZ//ωB97X-D/6-31++G(d,p) level of theory. The calculated binding free energies were used to evaluate the cluster stabilities for population dynamics simulations. The resultant SA-driven NPF rates and synergies of the studied bases are presented to show that DMA and EDA act as nucleators (although EDA becomes weak in large clusters), TMA acts as a catalyzer, and AM/MA is often overshadowed by strong bases.

Look Up: Probing the Vertical Profile of New Particle Formation and Growth in the Planetary Boundary Layer With Models and Observations

AbstractThe processes of new particle formation (NPF) and growth are important contributors to cloud condensation nuclei (CCN) concentrations, and CCN are important for climate from their impact on planetary radiative forcing. While the general ubiquity and importance of NPF is understood, the vertical extent and governing mechanisms of NPF and growth in the lower troposphere are uncertain. We present an analysis of four NPF events and two non‐NPF events during the HI‐SCALE field campaign at the Southern Great Plains observatory in Oklahoma, USA. First, we analyzed airborne and ground‐based observations of aerosol and gas‐phase properties. Second, we used a column aerosol chemistry and microphysics model to probe factors that influence the vertical profile of NPF. During HI‐SCALE, we found several instances of enhanced NPF occurring several hundred meters above the surface; however, the spatio‐temporal characteristics of the observed NPF made comparisons between airborne‐ and ground‐based observations difficult. The model represented the observed NPF (or lack of NPF) and particle growth at the surface to final diameters within 10 nm. The model predicted enhanced NPF rates in the upper mixed layer, and this enhancement is primarily due to the temperature dependence in the NPF schemes, but this was also dependent on the vertical profile of gas‐phase precursors measured during HI‐SCALE. We found vertical mixing in the model either enhanced or suppressed NPF rates, aerosol number concentrations, and particle growth rates at the surface. Finally, our analysis provides insights for future field campaigns and modeling efforts investigating the vertical profile of NPF.

The missing base molecules in atmospheric acid–base nucleation

Transformation of low-volatility gaseous precursors to new particles affects aerosol number concentration, cloud formation and hence the climate. The clustering of acid and base molecules is a major mechanism driving fast nucleation and initial growth of new particles in the atmosphere. However, the acid–base cluster composition, measured using state-of-the-art mass spectrometers, cannot explain the measured high formation rate of new particles. Here we present strong evidence for the existence of base molecules such as amines in the smallest atmospheric sulfuric acid clusters prior to their detection by mass spectrometers. We demonstrate that forming (H2SO4)1(amine)1 is the rate-limiting step in atmospheric H2SO4-amine nucleation and the uptake of (H2SO4)1(amine)1 is a major pathway for the initial growth of H2SO4 clusters. The proposed mechanism is very consistent with measured new particle formation in urban Beijing, in which dimethylamine is the key base for H2SO4 nucleation while other bases such as ammonia may contribute to the growth of larger clusters. Our findings further underline the fact that strong amines, even at low concentrations and when undetected in the smallest clusters, can be crucial to particle formation in the planetary boundary layer.

The driving factors of new particle formation and growth in the polluted boundary layer

Abstract. New particle formation (NPF) is a significant source of atmospheric particles, affecting climate and air quality. Understanding the mechanisms involved in urban aerosols is important to develop effective mitigation strategies. However, NPF rates reported in the polluted boundary layer span more than 4 orders of magnitude, and the reasons behind this variability are the subject of intense scientific debate. Multiple atmospheric vapours have been postulated to participate in NPF, including sulfuric acid, ammonia, amines and organics, but their relative roles remain unclear. We investigated NPF in the CLOUD chamber using mixtures of anthropogenic vapours that simulate polluted boundary layer conditions. We demonstrate that NPF in polluted environments is largely driven by the formation of sulfuric acid–base clusters, stabilized by the presence of amines, high ammonia concentrations and lower temperatures. Aromatic oxidation products, despite their extremely low volatility, play a minor role in NPF in the chosen urban environment but can be important for particle growth and hence for the survival of newly formed particles. Our measurements quantitatively account for NPF in highly diverse urban environments and explain its large observed variability. Such quantitative information obtained under controlled laboratory conditions will help the interpretation of future ambient observations of NPF rates in polluted atmospheres.

In situ observation of new particle formation (NPF) in the tropical tropopause layer of the 2017 Asian monsoon anticyclone – Part 2: NPF inside ice clouds

Abstract. From 27 July to 10 August 2017, the airborne StratoClim mission took place in Kathmandu, Nepal, where eight mission flights were conducted with the M-55 Geophysica up to altitudes of 20 km. New particle formation (NPF) was identified by the abundant presence of nucleation-mode aerosols, with particle diameters dp smaller than 15 nm, which were in-situ-detected by means of condensation nuclei (CN) counter techniques. NPF fields in clear skies as well as in the presence of cloud ice particles (dp > 3 µm) were encountered at upper troposphere–lowermost stratosphere (UTLS) levels and within the Asian monsoon anticyclone (AMA). NPF-generated nucleation-mode particles in elevated concentrations (Nnm) were frequently found together with cloud ice (in number concentrations Nice of up to 3 cm−3) at heights between ∼ 11 and 16 km. From a total measurement time of ∼ 22.5 h above 10 km altitude, in-cloud NPF was in sum detected over ∼ 1.3 h (∼ 50 % of all NPF records throughout StratoClim). Maximum Nnm of up to ∼ 11 000 cm−3 was detected coincidently with intermediate ice particle concentrations Nice of 0.05–0.1 cm−3 at comparatively moderate carbon monoxide (CO) contents of ∼ 90–100 nmol mol−1. Neither under clear-sky nor during in-cloud NPF do the highest Nnm concentrations correlate with the highest CO mixing ratios, suggesting that an elevated pollutant load is not a prerequisite for NPF. Under clear-air conditions, NPF with elevated Nnm (> 8000 cm−3) occurred slightly less often than within clouds. In the presence of cloud ice, NPF with Nnm between 1500–4000 cm−3 was observed about twice as often as under clear-air conditions. NPF was not found when ice water contents exceeded 1000 µmol mol−1 in very cold air (< 195 K) at tropopause levels. This indicates a reduction in NPF once deep convection is prevalent together with the presence of mainly liquid-origin ice particles. Within in situ cirrus near the cold point tropopause, recent NPF or intense events with mixing ration nnm larger than 5000 mg−1 were observed only in about 6 % of the in-cloud NPF data. In determining whether the cloud-internal NPF is attenuated or prevented by the microphysical properties of cloud elements, the integral radius (IR) of the ice cloud population turned out to be indicative. Neither the number of ice particles nor the free distance between the ice particles is clearly related to the NPF rate detected. While the increase in ice particles' mass per time dmdt is proportional to the IR and mainly due to the condensation of water vapour, additional condensation of NPF precursors proceeds at the expense of the NPF rate as the precursor's saturation ratio declines. Numerical simulations show the impact of the IR on the supersaturation of a condensable vapour, such as sulfuric acid, and furthermore illustrate that the IR of the cloud ice determines the effective limitation of NPF rates.

Factors Influencing New Atmospheric Particle Formation in Ordos During Summer and Autumn 2019

In this study, the aerosol number size distribution in the range of 10 nm-10 μm was collected from August 16 to October 04, 2019 at Ordos using a wide-range particle spectrometer (WPS). Combined with PM (PM2.5 and PM10), pollution gases, meteorological data, and the HYSPLIT model, the characteristics and impact factors of new particle formation (NPF) were discussed. The results indicated that there were 19 NPF events during the observation period, which have different effects on diurnal variation in aerosol number concentration in different modes. The NPF events caused a sharp increase in the number concentration of nucleation and Aitken mode aerosols, but had little effect on the number concentration of accumulation and coarse mode aerosols. The temperature, wind speed, and total solar radiation during NPF days were usually higher than those in non-NPF days, and the RH during NPF days was lower. On NPF days, the mass concentrations of PM2.5, PM10, CO, and NO2 were lower than those on non-NPF days, while the mass concentrations of O3 and SO2 were higher. NPF events were observed in 40.0% of northern air masses and 29.6% of southern air masses. There were significant differences in meteorological elements in different NPF event air mass types. The southern NPF event air mass type had the lowest wind speed and the highest RH, with averages of (2.4±1.5) m·s-1 and (48.8±10.8)%, respectively. The northern NPF event air mass type had the highest wind speed and total solar radiation, with averages of (4.2±1.9) m·s-1 and (664.5±255.6) W·m-2, respectively. The western air mass type of NPF event had the lowest RH, with an average of (29.8±12.7)%. The formation rates of new particles in the different air mass types of NPF events were similar, ranging from 1.5 to 1.8 cm-3·s-1. The largest growth rate was (12.7±13.6) nm·h-1 in the southern NPF event air mass type, which was 1.2 times and 1.4 times higher than the NPF events of northern air masses and western air masses.

High concentration of ultrafine particles in the Amazon free troposphere produced by organic new particle formation

The large concentrations of ultrafine particles consistently observed at high altitudes over the tropics represent one of the world's largest aerosol reservoirs, which may be providing a globally important source of cloud condensation nuclei. However, the sources and chemical processes contributing to the formation of these particles remain unclear. Here we investigate new particle formation (NPF) mechanisms in the Amazon free troposphere by integrating insights from laboratory measurements, chemical transport modeling, and field measurements. To account for organic NPF, we develop a comprehensive model representation of the temperature-dependent formation chemistry and thermodynamics of extremely low volatility organic compounds as well as their roles in NPF processes. We find that pure-organic NPF driven by natural biogenic emissions dominates in the uppermost troposphere above 13 km and accounts for 65 to 83% of the column total NPF rate under relatively pristine conditions, while ternary NPF involving organics and sulfuric acid dominates between 8 and 13 km. The large organic NPF rates at high altitudes mainly result from decreased volatility of organics and increased NPF efficiency at low temperatures, somewhat counterbalanced by a reduced chemical formation rate of extremely low volatility organic compounds. These findings imply a key role of naturally occurring organic NPF in high-altitude preindustrial environments and will help better quantify anthropogenic aerosol forcing from preindustrial times to the present day.

Atmospheric Sulfuric Acid‐Dimethylamine Nucleation Enhanced by Trifluoroacetic Acid

AbstractSulfuric acid (SA)‐dimethylamine (DMA)‐H2O cluster formation has been proven to be responsible for a significant part of new particle formation (NPF) in a Chinese megacity. However, the possible involvement of common atmospheric acids in the subsequent growth of SA‐DMA clusters remains elusive. We simulated formation and growth of clusters using atmospheric relevant concentrations of SA, DMA, and trifluoroacetic acid (TFA), a commonly observed atmospheric perfluorocarboxylic acid, using Density Functional Theory combined with Atmospheric Cluster Dynamics Code. The presence of TFA leads to complex cluster formation routes and an enhancement of NPF rates by up to 2.3 ([TFA] = 5.0 × 106 molecules cm−3, [SA] = 1.0 × 106 molecules cm−3, and [DMA] = 1.5 × 109 molecules cm−3). The agreement of (SA)1·(DMA)1‐2·(TFA)1 concentrations between simulations and ambient measurements during NPF events validates model predictions and implies that perfluorocarboxylic acids could potentially boost atmospheric SA‐DMA NPF rates.

Influence of atmospheric conditions on sulfuric acid-dimethylamine-ammonia-based new particle formation.

A recent quantitative measurement of rates of new particle formation (NPF) in urban Shanghai showed that the high rates of NPF can be largely attributed to the sulfuric acid (SA)-dimethylamine (DMA) nucleation due to relatively high DMA concentration in urban atmosphere (Yao etal., Science. 2018, 361, 278). In certain atmospheric conditions, the release of DMA is accompanied with the emission of high concentration of ammonia. As a result, the ammonia (A) may participate in SA-DMA-based NPF. However, the main sources of DMA and A can be different, thereby leading to different mechanism for the SA-DMA-A-based nucleation under different atmospheric conditions. Near industrial sources with relatively high DMA concentration of 108 molecules cm-3, the contribution of binary SA-DMA nucleation to cluster formation is 61% at 278K, representing a dominant pathway for NPF. However, in the region not too close to major source of DMA emission, e.g., near agriculture farmland, the routes involving ternary SA-DMA-A nucleation make a 64% contribution at 278K with DMA concentration of 107 molecules cm-3, showing that A has marked impact on the cluster formation. Under such a condition, we predict that coexisting DMA and A could be detected in the process of NPF. Moreover, at winter temperatures or at higher altitudes, our calculations suggest that the clustering of initial clusters likely involve ternary SA-DMA-A clusters rather than binary SA-DMA clusters. These new insights may be helpful to analyze and predict atmospheric-condition-dependent NFP in either urban or rural regions and/or in different season of the year.

Effect of the molecular structure of volatile organic compounds on atmospheric nucleation: A modeling study based on gas kinetic theory and graph theory

Severe PM2.5 (particulate matter with aerodynamic diameter smaller than 2.5 μm) pollution in China, with adverse impact on human health and global climate change, has raised great concern in recent years. The volatile organic compound (VOC) is suggested to be a significant precursor of PM2.5, but which VOC structure contributes the most to the aerosol particulate formation is still an open question. With large space occupation and complex structures (cyclic, linear and branched), VOCs together with inorganics may play a critical role in atmospheric new particle formation (NPF). To explore the effect of molecular structure on nucleation in NPF, a multi-component (H2SO4-HNO3-NH3-VOC) kinetic model is established based on the gas kinetic theory and graph theory. As the most common VOCs in the atmosphere, alkanes with 2–15 carbons are selected for model analysis. The results show that alkanes especially those with a cyclic structure or carbon number ≥4 results in the highest rate of NPF within the species considered in this study. The dominant size of nuclei, as well as the concentration of particles (larger than 1 nm), is enhanced by the increasing carbon number in alkanes. Taking the alkanes with same carbon number for comparison, the contribution to the nucleation by molecular structure is found to follow the order cyclic>linear>branched, and inversely proportion to branching number.

New particle formation in the marine atmosphere during seven cruise campaigns

Abstract. We measured the particle number concentration, size distribution, and new particle formation (NPF) events in the marine atmosphere during six cruise campaigns over the marginal seas of China in 2011–2016 and one campaign from the marginal seas to the Northwest Pacific Ocean (NWPO) in 2014. We observed relatively frequent NPF events in the atmosphere over the marginal seas of China, i.e., on 23 out of 126 observational days, with the highest frequency of occurrence in fall, followed by spring and summer. In total, 22 out of 23 NPF events were found to be associated with the long-range transport of continental pollutants based on 24 h air mass back trajectories and pre-existing particle number concentrations, which largely exceeded the clean marine background, leaving one much weaker NPF event that was likely induced by oceanic precursors alone, as supported by multiple independent pieces of evidence. Although the long-range transport signal of continental pollutants can be clearly observed in the remote marine atmosphere over the NWPO, NPF events were observed on only 2 out of 36 days. The nucleation-mode particles (<30 nm), however, accounted for as high as 35 %±13 % of the total particle number concentration during the NWPO cruise campaign, implying the existence of many undetected NPF events in the near-sea-level atmosphere or above. To better characterize NPF events, we introduce a term called the net maximum increase in the nucleation-mode particle number concentration (NMINP) and correlate it with the formation rate of new particles (FR). We find a moderately good linear correlation between NMINP and FR at FR≤8 cm−3 s−1, but no correlation exists at FR>8 cm−3 s−1. The possible mechanisms are argued in terms of the roles of different vapor precursors. We also find that a ceiling exists for the growth of new particles from 10 nm to larger sizes in most NPF events. We thereby introduce a term called the maximum geometric median diameter of new particles (Dpgmax) and correlate it with the growth rate of new particles (GR). A moderately good linear correlation is also obtained between the Dpgmax and GR, and only GR values larger than 7.9 nm h−1 can lead to new particles growing with a Dpgmax beyond 50 nm based on the equation. By combining simultaneous measurements of the particle number size distributions and cloud condensation nuclei (CCN) at different super saturations (SS), we observed a clear increase in CCN when the Dpg of new particles exceeded 50 nm at SS=0.4 %. However, this case did not occur for SS=0.2 %. Consistent with the results of previous studies in the continental atmosphere, our results imply that particles smaller than 50 nm are unlikely activated as CCN at SS=0.4 % in the marine atmosphere. Moreover, κ decrease from 0.4 to 0.1 during the growth period of new particles, implying that organics likely overwhelm the growth of new particles to CCN size. The chemical analysis of nano-Micro-Orifice Uniform Deposit Impactor (nano-MOUDI) samples reveals that trimethylamine (TMA) and oxalic acid might appreciably contribute to the growth of new particles in some cases.

The influence of wind speed on new particle formation events in an urban environment

New particle formation (NPF) is a common occurrence in urban environments where it is promoted by a ready supply of gaseous precursors such as sulfuric acid, ammonium and volatile organic compounds originating mainly from motor vehicle emissions. In this paper, we investigate the influence of wind speed on the occurrence of NPF events in a subtropical urban environment. The analysis was based on a large data set obtained with a neutral cluster and air ion spectrometer (NAIS) over 485 days of observations, out of which NPF events were observed on 213 days. Particles formation was most likely to occur during the morning hours and we observed NPF events between 8 am and noon on 123 of these days. In order to assess its influence, we estimated the mean wind speed between 8 and 9 am on these 123 days and on the days with no NPF. We found a statistically significant difference in average wind speeds during days with NPF (1.31 m s−1) and days with no NPF (1.84 m s−1) (p < 0.05). Several studies have shown that increasing wind speed enhances NPF in polluted megacities by removing pre-existing particles. Our observations indicate that this effect is less important in smaller cities, so that higher wind speeds can mitigate NPF by the removal of condensable gases. The wind speed does not affect the rate of NPF in clean environments.

Self-Catalytic Reaction of SO3 and NH3 To Produce Sulfamic Acid and Its Implication to Atmospheric Particle Formation.

Sulfur trioxide (SO3) is one of the most active chemical species in the atmosphere, and its atmospheric fate has profound implications to air quality and human health. The dominant gas-phase loss pathway for SO3 is generally believed to be the reaction with water molecules, resulting in sulfuric acid. The latter is viewed as a critical component in the new particle formation (NPF). Herein, a new and competitive loss pathway for SO3 in the presence of abundant gas-phase ammonia (NH3) species is identified. Specifically, the reaction between SO3 and NH3, which produces sulfamic acid, can be self-catalyzed by the reactant (NH3). In dry and heavily polluted areas with relatively high concentrations of NH3, the effective rate constant for the bimolecular SO3-NH3 reaction can be sufficiently fast through this new loss pathway for SO3 to become competitive with the conventional loss pathway for SO3 with water. Furthermore, this study shows that the final product of the reaction, namely, sulfamic acid, can enhance the fastest possible rate of NPF from sulfuric acid and dimethylamine (DMA) by about a factor of 2. An alternative source of stabilizer for acid-base clustering in the atmosphere is suggested, and this new mechanism for NPF has potential to improve atmospheric modeling in highly polluted regions.

Atmospheric new particle formation from sulfuric acid and amines in a Chinese megacity.

Atmospheric new particle formation (NPF) is an important global phenomenon that is nevertheless sensitive to ambient conditions. According to both observation and theoretical arguments, NPF usually requires a relatively high sulfuric acid (H2SO4) concentration to promote the formation of new particles and a low preexisting aerosol loading to minimize the sink of new particles. We investigated NPF in Shanghai and were able to observe both precursor vapors (H2SO4) and initial clusters at a molecular level in a megacity. High NPF rates were observed to coincide with several familiar markers suggestive of H2SO4-dimethylamine (DMA)-water (H2O) nucleation, including sulfuric acid dimers and H2SO4-DMA clusters. In a cluster kinetics simulation, the observed concentration of sulfuric acid was high enough to explain the particle growth to ~3 nanometers under the very high condensation sink, whereas the subsequent higher growth rate beyond this size is believed to result from the added contribution of condensing organic species. These findings will help in understanding urban NPF and its air quality and climate effects, as well as in formulating policies to mitigate secondary particle formation in China.

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

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).

Experimental particle formation rates spanning tropospheric sulfuric acid and ammonia abundances, ion production rates, and temperatures

AbstractBinary nucleation of sulfuric acid and water as well as ternary nucleation involving ammonia are thought to be the dominant processes responsible for new particle formation (NPF) in the cold temperatures of the middle and upper troposphere. Ions are also thought to be important for particle nucleation in these regions. However, global models presently lack experimentally measured NPF rates under controlled laboratory conditions and so at present must rely on theoretical or empirical parameterizations. Here with data obtained in the European Organization for Nuclear Research CLOUD (Cosmics Leaving OUtdoor Droplets) chamber, we present the first experimental survey of NPF rates spanning free tropospheric conditions. The conditions during nucleation cover a temperature range from 208 to 298 K, sulfuric acid concentrations between 5 × 105 and 1 × 109 cm−3, and ammonia mixing ratios from zero added ammonia, i.e., nominally pure binary, to a maximum of ~1400 parts per trillion by volume (pptv). We performed nucleation studies under pure neutral conditions with zero ions being present in the chamber and at ionization rates of up to 75 ion pairs cm−3 s−1 to study neutral and ion‐induced nucleation. We found that the contribution from ion‐induced nucleation is small at temperatures between 208 and 248 K when ammonia is present at several pptv or higher. However, the presence of charges significantly enhances the nucleation rates, especially at 248 K with zero added ammonia, and for higher temperatures independent of NH3 levels. We compare these experimental data with calculated cluster formation rates from the Atmospheric Cluster Dynamics Code with cluster evaporation rates obtained from quantum chemistry.