New particle formation (NPF) is the source of over half of the atmosphere's cloud condensation nuclei, thus influencing cloud properties and Earth's energy balance. Unlike in the planetary boundary ...layer, few observations of NPF in the free troposphere exist. We provide observational evidence that at high altitudes, NPF occurs mainly through condensation of highly oxygenated molecules (HOMs), in addition to taking place through sulfuric acid–ammonia nucleation. Neutral nucleation is more than 10 times faster than ion-induced nucleation, and growth rates are size-dependent. NPF is restricted to a time window of 1 to 2 days after contact of the air masses with the planetary boundary layer; this is related to the time needed for oxidation of organic compounds to form HOMs. These findings require improved NPF parameterization in atmospheric models.
Formation of new aerosol particles from trace gases is a major source of cloud condensation nuclei (CCN) in the global atmosphere, with potentially large effects on cloud optical properties and ...Earth's radiative balance. Controlled laboratory experiments have resolved, in detail, the different nucleation pathways likely responsible for atmospheric new particle formation, yet very little is known from field studies about the molecular steps and compounds involved in different regions of the atmosphere. The scarcity of primary particle sources makes secondary aerosol formation particularly important in the Antarctic atmosphere. Here, we report on the observation of ion-induced nucleation of sulfuric acid and ammonia-a process experimentally investigated by the CERN CLOUD experiment-as a major source of secondary aerosol particles over coastal Antarctica. We further show that measured high sulfuric acid concentrations, exceeding 10
molecules cm
, are sufficient to explain the observed new particle growth rates. Our findings show that ion-induced nucleation is the dominant particle formation mechanism, implying that galactic cosmic radiation plays a key role in new particle formation in the pristine Antarctic atmosphere.
The formation of new aerosol particles in the atmosphere is a key process influencing the aerosol number concentration as well as the climate, in particular at high altitude, where the newly formed ...particles directly influence cloud formation. However, free tropospheric new particle formation (NPF) is poorly documented due to logistic limitations and complex atmospheric dynamics around high-altitude stations that make the observation of this day-time process challenging. Recent improvements in measurement techniques make now possible the detection of neutral clusters down to ~ 1 nm sizes, which opens new horizons in our understanding of the nucleation process. Indeed, only the charged fraction of clusters has been reported in the upper troposphere up to now. Here we report day-time concentrations of charged and neutral clusters (1 to 2.5 nm mobility diameter) recorded at the interface between the boundary layer (BL) and the FT as well as in the FT at the altitude site of Puy de Dôme (1465 m a.s.l.), central France, between 10 and 29 February 2012. Our findings demonstrate that in the FT, and especially at the interface between the BL and the FT, the formation of 1.5 nm neutral clusters significantly exceeds the one of ionic clusters during NPF events, clearly indicating that they dominate in the nucleation process. We also observe that the total cluster concentration significantly increases during NPF events compared to the other days, which was not clearly observed for the charged cluster population in the past. During the studied period, the nucleation process does not seem to be sulfuric acid-limited and could be promoted by the transport of pollutants to the upper troposphere, coupled with low temperatures.
The significance of ion–ion recombination for atmospheric new particle formation is not well quantified. Here we present and evaluate a method for determining the size distribution of recombination ...products from the size distributions of neutral and charged clusters. Our method takes into account the production of recombination products in the collisions between oppositely charged ions and the loss due to coagulation. Furthermore, unlike previous studies, we also consider the effect of condensational growth on the size distribution of recombination products. We applied our method to the data measured in Hyytiälä, Finland, to estimate the contribution of ion–ion recombination to the concentrations of atmospheric clusters in the size range of 0.9–2.1 nm. We observed that the concentration of recombination products was highest in the size classes between 1.5 and 1.9 nm. The median concentrations of recombination products were between 6 and 69 cm−3 in different size classes, which resulted in a small proportion of all neutral clusters, varying between 0.2 and 13%. When examining the whole size range between 0.9 and 2.1 nm, the median fraction of recombination products of all neutral clusters was only 1.5%. We also investigated how the results change if the effect of condensational growth is neglected. It seems that with that assumption the fragmentation of newly formed recombination products has to be taken into account, or else the concentration of recombination products is overestimated. Overall, we concluded that our method provides reasonable results, which are consistent with the earlier estimates on the contribution of recombination products to atmospheric cluster population in Hyytiälä. Still, in order to determine the size distribution of recombination products more accurately in the future, more precise measurements of the size distribution of atmospheric clusters would be needed.
The number of experiments characterizing sub-3nm aerosol particle dynamics has increased significantly over the recent years. In these experiments, it is essential to know/determine size resolved ...particle number concentrations accurately. Despite particle concentration measurement being relatively simple experiment, it can contain large uncertainties from various sources in the sub-3nm size range. In this study we aim to identify and examine some of these sources. We simulated four different condensation particle counters (CPCs) (TSI 3777, ADI vWCPC, Airmodus A11 and an ideal CPC with d50 (lowest detection threshold) of 1.5nm) and one differential mobility analyzer (DMA) (TSI nano DMA) and study the resulting uncertainties when using them to measure three different particle size distributions. First, we show that Poisson counting uncertainty √N represents the standard deviation, σ, of the number of counted particles in all CPC and DMPS counting experiments. Second, the state-of-the-art DMA-CPC particle sizing system is examined with respect to counting statistics. Third, the performance of the instruments is assumed to be well-known, and instrumental non-idealities and the inversion routine are assessed. Fourth, ± 0.5nm offset is inserted to the CPC d50, and its effect on the measured particle concentration is examined. Our results highlight the importance of knowing the CPC d50 accurately to narrow down the particle concentration uncertainty. Furthermore, the results show that the current DMA-CPC measurements are subject to considerable counting uncertainty in low particle concentration environments. Based on the analysis we summarize suggestions for further research and instrumental development for more accurate sub-3nm particle concentration measurements in the future.
•Uncertainties of sub-3nm particle concentration measurement were analysed.•Main sources of concentration uncertainty: steep size distributions and CPC cutoff.•DMPS counting uncertainties non-negligible in low particle concentration environments.
New particle formation (NPF) is one of the major sources of atmospheric ultrafine particles. Due to the high aerosol and trace gas concentrations, the mechanism and governing factors for NPF in the ...polluted atmospheric boundary layer may be quite different from those in clean environments, which is however less understood. Herein, based on long-term atmospheric measurements from January 2018 to March 2019 in Beijing, the nucleation mechanism and the influences of H2SO4 concentration, amine concentrations, and aerosol concentration on NPF are quantified. The
collision of H2SO4–amine clusters is found to be the dominating mechanism to initialize NPF in urban Beijing. The coagulation scavenging due to the high aerosol concentration is a governing factor as it limits the concentration of H2SO4–amine clusters and new particle formation rates. The formation of H2SO4–amine clusters in Beijing is sometimes limited by low amine concentrations. Summarizing the synergistic effects of H2SO4 concentration, amine concentrations, and aerosol concentration, we elucidate the governing factors for H2SO4–amine nucleation for various conditions.
Atmospheric new particle formation (NPF) occurs by the
formation of nanometer-sized molecular clusters and their subsequent growth
to larger particles. NPF involving sulfuric acid, bases and oxidized ...organic
compounds is an important source of atmospheric aerosol particles. One of the
mechanisms suggested to depict this process is nano-Köhler theory, which
describes the activation of inorganic molecular clusters to growth by a
soluble organic vapor. In this work, we studied the capability of
nano-Köhler theory to describe the initial growth of atmospheric
molecular clusters by simulating the dynamics of a cluster population in the
presence of a sulfuric acid–base mixture and an organic compound. We
observed nano-Köhler-type activation in our simulations when the
saturation ratio of the organic vapor and the ratio between organic and
inorganic vapor concentrations were in a suitable range. However,
nano-Köhler theory was unable to predict the exact size at which the
activation occurred in the simulations. In some conditions, apparent cluster
growth rate (GR) started to increase close to the activation size determined
from the simulations. Nevertheless, because the behavior of GR is also
affected by other dynamic processes, GR alone cannot be used to deduce the
cluster growth mechanism.
Atmospheric new particle formation (NPF) events are regularly observed in
urban Beijing, despite high concentrations of background particles which,
based on theory, should inhibit NPF due to high ...values of coagulation sink
(CoagS). The survival probability, which depends on both CoagS and particle
growth rate (GR), is a key parameter in determining the occurrence of NPF events
as it describes the fraction of newly formed particles that survive from a
smaller diameter to a larger diameter. In this study, we investigate and
compare survival probabilities from 1.5 to 3 nm (J3/J1.5), from 3 to
6 nm (J6/J3), and from 6 to 10 nm (J10/J6) based on analytical
formulae, cluster population simulations, and atmospheric observations from
Beijing. We find that survival probabilities based on the cluster population
simulations and one of the analytical formulae are in a good agreement.
However, at low ratios between the background condensation sink (CS) and GR,
and at high concentrations of sub-3 nm clusters, cluster–cluster collisions
efficiently lower survival probabilities in the cluster population
simulations. Due to the large concentrations of clusters and small particles
required to considerably affect the survival probabilities, we consider it
unlikely that cluster–cluster collisions significantly affect atmospheric
survival probabilities. The values of J10/J6 observed in Beijing show
high variability, most likely due to influences of primary particle
emissions, but are on average in relatively good agreement with the values
based on the simulations and the analytical formulae. The observed values of
J6/J3 are mostly lower than those predicted based on the simulations
and the analytical formulae, which could be explained by uncertainties in CS
and GR. The observed values of J3/J1.5 at high CS / GR are much higher
than predicted based on the simulations and the analytical formulae. We argue
that uncertainties in GR or CS are unlikely to solely explain the observed
values of J3/J1.5 under high CS conditions. Thus, further work is
needed to better understand the factors influencing survival probabilities
of sub-3 nm atmospheric particles in polluted environments.
New particle formation (NPF) events have been observed all around the world and are known to be a major source of atmospheric aerosol particles. Here we combine 20 years of observations in a boreal ...forest at the SMEAR II station (Station for Measuring Ecosystem–Atmosphere Relations) in Hyytiälä, Finland, by building on previously accumulated knowledge and by focusing on clear-sky (noncloudy) conditions. We first investigated the effect of cloudiness on NPF and then compared the NPF event and nonevent days during clear-sky conditions. In this comparison we considered, for example, the effects of calculated particle formation rates, condensation sink, trace gas concentrations and various meteorological quantities in discriminating NPF events from nonevents. The formation rate of 1.5 nm particles was calculated by using proxies for gaseous sulfuric acid and oxidized products of low volatile organic compounds, together with an empirical nucleation rate coefficient. As expected, our results indicate an increase in the frequency of NPF events under clear-sky conditions in comparison to cloudy ones. Also, focusing on clear-sky conditions enabled us to find a clear separation of many variables related to NPF. For instance, oxidized organic vapors showed a higher concentration during the clear-sky NPF event days, whereas the condensation sink (CS) and some trace gases had higher concentrations during the nonevent days. The calculated formation rate of 3 nm particles showed a notable difference between the NPF event and nonevent days during clear-sky conditions, especially in winter and spring. For springtime, we are able to find a threshold equation for the combined values of ambient temperature and CS, (CS (s−1) > −3.091 × 10−5 × T (in Kelvin) + 0.0120), above which practically no clear-sky NPF event could be observed. Finally, we present a probability distribution for the frequency of NPF events at a specific CS and temperature.
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