Seasonal variation of aerosol water uptake and its impact on the direct radiative effect at Ny-Ålesund, Svalbard

© Author(s) 2014. This work is distributed under the Creative Commons Attribution 3.0 LicenseIn this study we investigated the impact of water uptake by aerosol particles in ambient atmosphere on their optical properties and their direct radiative effect (ADRE, W m-2) in the Arctic at Ny-Ålesund, Svalbard, during 2008. To achieve this, we combined three models, a hygroscopic growth model, a Mie model and a radiative transfer model, with an extensive set of observational data. We found that the seasonal variation of dry aerosol scattering coefficients showed minimum values during the summer season and the beginning of fall (July-August-September), when small particles (< 100 nm in diameter) dominate the aerosol number size distribution. The maximum scattering by dry particles was observed during the Arctic haze period (March-April-May) when the average size of the particles was larger. Considering the hygroscopic growth of aerosol particles in the ambient atmosphere had a significant impact on the aerosol scattering coefficients: the aerosol scattering coefficients were enhanced by on average a factor of 4.30 ± 2.26 (mean ± standard deviation), with lower values during the haze period (March-April-May) as compared to summer and fall. Hygroscopic growth of aerosol particles was found to cause 1.6 to 3.7 times more negative ADRE at the surface, with the smallest effect during the haze period (March-April-May) and the highest during late summer and beginning of fall (July-August-September).Peer reviewe

An improved criterion for new particle formation in diverse atmospheric environments

A dimensionless theory for new particle formation (NPF) was developed, using an aerosol population balance model incorporating recent developments in nucleation rates and measured particle growth rates. Based on this theoretical analysis, it was shown that a dimensionless parameter &lt;i&gt;L&lt;/i&gt;&lt;sub&gt;&amp;Gamma;&lt;/sub&gt;, characterizing the ratio of the particle scavenging loss rate to the particle growth rate, exclusively determined whether or not NPF would occur on a particular day. This parameter determines the probability that a nucleated particle will grow to a detectable size before being lost by coagulation with the pre-existing aerosol. Cluster-cluster coagulation was shown to contribute negligibly to this survival probability under conditions pertinent to the atmosphere. Data acquired during intensive measurement campaigns in Tecamac (MILAGRO), Atlanta (ANARChE), Boulder, and Hyytiälä (QUEST II, QUEST IV, and EUCAARI) were used to test the validity of &lt;i&gt;L&lt;/i&gt;&lt;sub&gt;&amp;Gamma;&lt;/sub&gt; as an NPF criterion. Measurements included aerosol size distributions down to 3 nm and gas-phase sulfuric acid concentrations. The model was applied to seventy-seven NPF events and nineteen non-events (characterized by growth of pre-existing aerosol without NPF) measured in diverse environments with broad ranges in sulfuric acid concentrations, ultrafine number concentrations, aerosol surface areas, and particle growth rates (nearly two orders of magnitude). Across this diverse data set, a nominal value of &lt;i&gt;L&lt;/i&gt;&lt;sub&gt;&amp;Gamma;&lt;/sub&gt;=0.7 was found to determine the boundary for the occurrence of NPF, with NPF occurring when &lt;i&gt;L&lt;/i&gt;&lt;sub&gt;&amp;Gamma;&lt;/sub&gt;&lt;0.7 and being suppressed when &lt;i&gt;L&lt;/i&gt;&lt;sub&gt;&amp;Gamma;&lt;/sub&gt;&gt;0.7. Moreover, nearly 45% of measured &lt;i&gt;L&lt;/i&gt;&lt;sub&gt;&amp;Gamma;&lt;/sub&gt; values associated with NPF fell in the relatively narrow range of 0.1&lt;&lt;i&gt;L&lt;/i&gt;&lt;sub&gt;&amp;Gamma;&lt;/sub&gt;&lt;0.3

Habitat selection of the mud crab Rhithropanopeus harrisii in its newly invaded range

Information on the habitat selection by non-indigenous species is crucial for understanding their effects on the communities to which they are introduced, since the effects are often focused on the invaded habitats. The North American mud crab Rhithropanopeus harrisii is a new invader in the northern Baltic Sea, on the coasts of Finland and Estonia. In the Finnish Archipelago Sea, it has been found in two very distinct habitats: reed belts of Phragmites australis and algal zones with Fucus vesiculosus as the main habitat-forming species. In previous studies in the Baltic Sea, R. harrisii has preferred F. vesiculosus and has locally driven a shift in the structure of F. vesiculosus-associated invertebrate communities. Here, we disentangled whether habitat choice was determined by habitat structure or the availability of food. First, we conducted a habitat selection experiment with P. australis and F. vesiculosus habitats and varying food availability, and found that R. harrisii preferred F. vesiculosus, with food having no effect on the habitat choice. Second, we studied if the preference for F. vesiculosus was due to the alga itself or the rocks it grows on. We found that R. harrisii preferred the shelter of the rock habitat, indicating that R. harrisii choose their habitat based on habitat structure rather than food availability in the habitat. However, the preference for sheltered rocky bottom habitats also exposes the associated F. vesiculosus communities to the impacts of R. harrisii through predation.Peer reviewe

Identification and classification of the formation of intermediate ions measured in boreal forest

International audienceWe have measured the size distributions of air ions (0.42?7.5 nm in diameter) with the Balanced Scanning Mobility Analyzer in boreal forest, in Southern Finland since spring 2003. The size range covers the size range of cluster ions (approximately 0.42?1.6 nm) and naturally charged nanometre aerosol particles (1.6?7.5 nm) or intermediate air ions. Based on the measurements from April 2003 to March 2006 we studied the characteristics of charged aerosol particle formation by classifying each day either as a particle formation event, undefined or non-event day. The principal of the classification, as well as the statistical description of the charged aerosol particle formation events are given. We found in total 270 (26% of the analysed days) and 226 (22% of the analysed days) particle formation days for negative and positive intermediate ions, respectively. For negatively charged particles we classified 411 (40% of the analysed days) undefined and 348 (34% of the analysed days) non-event days whereas for positively charged particles 343 (33% of the analysed days) undefined and 460 (45% of the analysed days) non-event days. The results were compared with the ordinary classification based on the Differential Mobility Particle Sizer (DMPS) measurements carried out at the same place. The above-presented values differed slightly from that found from the DMPS data, with a lower particle diameter of 3 nm. In addition, we have found the rain-induced intermediate ion bursts frequently. The rain effect was detected on 163 days by means of negative ions and on 105 days by positive ones. Another interesting phenomenon among the charged aerosol particles was the appearance and existence of intermediate ions during the snowfall. We observed this phenomenon 24 times with negatively charged particles and 21 times with positively charged ones during winter months (October?April). These intermediate air ions were seen during the snowfall and may be caused by ice crystals, although the origin of these intermediate ions is unclear at the moment

Aerosol dynamics simulations on the connection of sulphuric acid and new particle formation

International audienceWe have performed a series of simulations with an aerosol dynamics box model to study the connection between new particle formation and sulphuric acid concentration. For nucleation either activation mechanism with a linear dependence on the sulphuric acid concentration or ternary H2O-H2SO4-NH3 nucleation was assumed. We investigated the factors that affect the sulphuric acid dependence during the early stages of particle growth, and tried to find conditions which would yield the linear dependence between the particle number concentration at 3?6 nm and sulphuric acid, as observed in field experiments. The simulations showed that the correlation with sulphuric acid may change during the growth from nucleation size to 3?6 nm size range, the main reason being the size dependent growth rate between 1 and 3 nm. In addition, the assumed size for the nucleated clusters had a crucial impact on the sulphuric acid dependence at 3 nm. The simulations yielded a linear dependence between the particle number concentration at 3 nm and sulphuric acid, when a low saturation vapour pressure for the condensable organic vapour was assumed, or when nucleation took place at ~2 nm instead of ~1 nm. Comparison of results with activation and ternary nucleation showed that ternary nucleation cannot explain the experimentally observed linear or square dependence on sulphuric acid

Classifying previously undefined days from eleven years of aerosol-particle-size distribution data from the SMEAR II station, Hyytiälä, Finland

Peer reviewe

Formation and growth of nucleated particles into cloud condensation nuclei: Model-measurement comparison

Aerosol nucleation occurs frequently in the atmosphere and is an important source of particle number. Observations suggest that nucleated particles are capable of growing to sufficiently large sizes that they act as cloud condensation nuclei (CCN), but some global models have reported that CCN concentrations are only modestly sensitive to large changes in nucleation rates. Here we present a novel approach for using long-term size distribution observations to evaluate a global aerosol model's ability to predict formation rates of CCN from nucleation and growth events. We derive from observations at five locations nucleation-relevant metrics such as nucleation rate of particles at diameter of 3 nm (J3), diameter growth rate (GR), particle survival probability (SP), condensation and coagulation sinks, and CCN formation rate (J100). These quantities are also derived for a global microphysical model, GEOS-Chem-TOMAS, and compared to the observations on a daily basis. Using GEOS-Chem-TOMAS, we simulate nucleation events predicted by ternary (with a 10−5 tuning factor) or activation nucleation over one year and find that the model slightly understates the observed annual-average CCN formation mostly due to bias in the nucleation rate predictions, but by no more than 50% in the ternary simulations. At the two locations expected to be most impacted by large-scale regional nucleation, Hyytiälä and San Pietro Capofiume, predicted annual-average CCN formation rates are within 34 and 2% of the observations, respectively. Model-predicted annual-average growth rates are within 25% across all sites but also show a slight tendency to underestimate the observations, at least in the ternary nucleation simulations. On days that the growing nucleation mode reaches 100 nm, median single-day survival probabilities to 100 nm for the model and measurements range from less than 1–6% across the five locations we considered; however, this does not include particles that may eventually grow to 100 nm after the first day. This detailed exploration of new particle formation and growth dynamics adds support to the use of global models as tools for assessing the contribution of microphysical processes such as nucleation to the total number and CCN budget

The roles of the atmosphere and ocean in driving Arctic warming due to European aerosol reductions

Clean air policies can have significant impacts on climate in remote regions. Previous modeling studies have shown that the temperature response to European sulfate aerosol reductions is largest in the Arctic. Here, we investigate the atmospheric and ocean roles in driving this enhanced Arctic warming using a set of fully‐coupled and slab‐ocean simulations (specified ocean heat convergence fluxes) with the Norwegian Earth system model (NorESM), under scenarios with high and low European aerosol emissions relative to year 2000. We show that atmospheric processes drive most of the Arctic response. The ocean pathway plays a secondary role inducing small temperature changes mostly in the opposite direction of the atmospheric response. Important modulators of the temperature response patterns are changes in sea‐ice extent and subsequent turbulent heat flux exchange, suggesting that a proper representation of Arctic sea‐ice and turbulent changes are key to predicting the Arctic response to mid‐latitude aerosol forcing

Connections between atmospheric sulphuric acid and new particle formation during QUEST III–IV campaigns in Heidelberg and Hyytiälä

This study investigates the connections between atmospheric sulphuric acid and new particle formation during QUEST III and BACCI/QUEST IV campaigns. The campaigns have been conducted in Heidelberg (2004) and Hyytiälä (2005), the first representing a polluted site surrounded by deciduous forest, and the second a rural site in a boreal forest environment. We have studied the role of sulphuric acid in particle formation and growth by determining 1) the power-law dependencies between sulphuric acid ([H2SO4]), and particle concentrations (N3−6) or formation rates at 1 nm and 3 nm (J1 and J3); 2) the time delays between [H2SO4] and N3−6 or J3, and the growth rates for 1–3 nm particles; 3) the empirical nucleation coefficients A and K in relations J1=A[H2SO4] and J1=K[H2SO4]^2, respectively; 4) theoretical predictions for J1 and J3 for the days when no significant particle formation is observed, based on the observed sulphuric acid concentrations and condensation sinks. In both environments, N3−6 or J3 and [H2SO4] were linked via a power-law relation with exponents typically ranging from 1 to 2. The result suggests that the cluster activation theory and kinetic nucleation have the potential to explain the observed particle formation. However, some differences between the sites existed: The nucleation coefficients were about an order of magnitude greater in Heidelberg than in Hyytiälä conditions. The time lags between J3 and [H2SO4] were consistently lower than the corresponding delays between N3−6 and [H2SO4]. The exponents in the J3/[H2SO4]^n_(J3)-connection were consistently higher than or equal to the exponents in the relation N3−6/[H2SO4]^n_(N36). In the J1 values, no significant differences were found between the observed rates on particle formation event days and the predictions on non-event days. The J3 values predicted by the cluster activation or kinetic nucleation hypotheses, on the other hand, were considerably lower on non-event days than the rates observed on particle formation event days. This study provides clear evidence implying that the main process limiting the observable particle formation is the competition between the growth of the freshly formed particles and their loss by scavenging, rather than the initial particle production by nucleation of sulphuric acid. In general, it can be concluded that the simple models based on sulphuric acid concentrations and particle formation by cluster activation or kinetic nucleation can predict the occurence of atmospheric particle formation and growth well, if the particle scavenging is accurately accounted for