Ion production rate in a boreal forest based on ion, particle and radiation measurements

Laakso, Lauri; Petäj̈ä, Tuukka; Lehtinen, K. E. J.; Kulmala, Markku; Paatero, Jussi; Hõrrak, Urmas; Tammet, Hannes; Joutsensaari, Jorma

doi:10.5194/acp-4-1933-2004

Cited by 133 publications

(138 citation statements)

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“…As the relative humidity at our site is very low during the particle formation and growth period (on average, 37 %), and the hygroscopic growth factors of the particles not known, CS was calculated for dry particle sizes. The hygroscopic growth of ambient aerosol particles is usually quite moderate at relative humidities below 50 % (Zhou, 2001;Laakso et al, 2004;Birmili et al, 2009;Wiedensohler et al, 2012) so our assumption of a dry particle radius should not cause a major error in calculating the value of CS.…”

Section: Data Analysis Methods Used On Measurement Datamentioning

confidence: 99%

Boundary layer nucleation as a source of new CCN in savannah environment

et al. 2013

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The South African savannah region is a complex environment of air pollution and natural emissions influenced by a strong seasonal cycle in biomass burning and strong precipitation. However, the scarcity of long-term observations means that the knowledge of controlling aerosol processes in this environment is limited. Here we use a recent dataset of 18 months of aerosol size distribution observations trying to understand the annual cycle of cloud condensation nuclei (CCN). Our observations show that the concentration of CCN-sized particles remains, in line with previous studies, high throughout the year with the highest concentrations during the dry winter and the lowest during the wet summer. During the wet season with reduced anthropogenic and biomass burning primary emissions, this pool of CCN is partly filled by boundary layer nucleation with subsequent growth. The enhanced importance of formation and growth during the wet season is addressed to increased biogenic activity together with enhanced free tropospheric removal decreasing the concentration of pre-existing CCN. During the dry season, while frequent new particle formation takes place, particle growth is reduced due to reduced condensing vapour concentrations. Thus in the dry season particles are not able to grow to sizes where they may act as CCN nearly as efficiently as during the wet season. The observations are compared to simulations by a global aerosol model GLOMAP. To our surprise, the global aerosol model utilized to explain the observations was not capable of re-producing the characteristics of particle formation and the annual CCN cycle, despite earlier good performance in predicting the particle concentrations in a number of diverse environments, including the South African savannah region. While the average yearly CCN concentrations of modelled CCN is close to observed concentrations, the characteristics of nucleation bursts and subsequent growth are not captured satisfactory by the model. Our sensitivity tests using different nucleation parameterizations and condensing organic vapour production rates show that neither of these is likely to explain the differences between observed and modelled nucleation and growth rates. A sensitivity study varying 28 modelling parameters indicates that the main uncertainties in the result are due to uncertainties in biomass burning emissions during the dry season, and anthropogenic sulphur emissions during the wet season, both in terms or emitted mass and particle sizes. The uncertainties appear to be mostly related to uncertainties in primary particle emissions, including the emissions variability not captured by monthly emission inventories. The results of this paper also highlights the fact that deficiencies in emissions estimates may result in deficiencies in particle production fluxes, while the end product such as modelled CCN concentration may be in line with observations

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Section: Data Analysis Methods Used On Measurement Datamentioning

confidence: 99%

Boundary layer nucleation as a source of new CCN in savannah environment

et al. 2013

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“…In the planetary boundary layer, the nucleation of H 2 SO 4 and an organic compound can be considered using either the cluster activation scheme of Kulmala et al (2006) and Riipinen et al (2007), or the kinetic nucleation scheme of Laakso et al (2004) and Kuang et al (2008) implementation these processes (when switched on) are limited to forested areas. Sensitivity experiments are performed with both schemes (HAM2 cluster and HAM2 kinetic in Table 4).…”

Section: Boundary Layer Nucleationmentioning

confidence: 99%

The global aerosol-climate model ECHAM-HAM, version 2: sensitivity to improvements in process representations

et al. 2012

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Abstract. This paper introduces and evaluates the second version of the global aerosol-climate model ECHAM-HAM. Major changes have been brought into the model, including new parameterizations for aerosol nucleation and water uptake, an explicit treatment of secondary organic aerosols, modified emission calculations for sea salt and mineral dust, the coupling of aerosol microphysics to a two-moment stratiform cloud microphysics scheme, and alternative wet scavenging parameterizations. These revisions extend the model's capability to represent details of the aerosol lifecycle and its interaction with climate. Nudged simulations of the year 2000 are carried out to compare the aerosol properties and global distribution in HAM1 and HAM2, and to evaluate them against various observations. Sensitivity experiments are performed to help identify the impact of each individual update in model formulation.Results indicate that from HAM1 to HAM2 there is a marked weakening of aerosol water uptake in the lower troposphere, reducing the total aerosol water burden from 75 Tg to 51 Tg. The main reason is the newly introduced κ-Köhler-theory-based water uptake scheme uses a lower value for the maximum relative humidity cutoff. Particulate organic matter loading in HAM2 is considerably higher in the upper troposphere, because the explicit treatment of secondary organic aerosols allows highly volatile oxidation products of the precursors to be vertically transported to regions of very low temperature and to form aerosols there. Sulfate, black carbon, particulate organic matter and mineral dust in HAM2 have longer lifetimes than in HAM1 because of weaker incloud scavenging, which is in turn related to lower autoconversion efficiency in the newly introduced two-moment cloud microphysics scheme. Modification in the sea salt emission scheme causes a significant increase in the ratio (from 1.6 to 7.7) between accumulation mode and coarse mode emission fluxes of aerosol number concentration. This leads to a general increase in the number concentration of smaller particles over the oceans in HAM2, as reflected by the higher Angström parameters.Evaluation against observation reveals that in terms of model performance, main improvements in HAM2 include a marked decrease of the systematic negative bias in the absorption aerosol optical depth, as well as smaller biases over the oceans inÅngström parameter and in the accumulation mode number concentration. The simulated geographical distribution of aerosol optical depth (AOD) is better correlated with the MODIS data, while the surface aerosol mass concentrations are very similar to those in the old version. The total aerosol water content in HAM2 is considerably Published by Copernicus Publications on behalf of the European Geosciences Union. K. Zhang et al.: Aerosol properties in ECHAM-HAM2closer to the multi-model average from Phase I of the AeroCom intercomparison project. Model deficiencies that require further efforts in the future include (i) positive biases in AOD over the ocean, (ii) n...

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“…For calculating the CS the dry size distribution measured with DMPS was converted into the ambient distribution using the parameterization by Laakso et al (2004). The transition regime correction factor for mass transfer β m was calculated with the expression by Fuchs and Sutugin (1970) using a value of 1 for mass accommodation coefficient.…”

Section: Concentrations ([Mt] [Oh] and [O 3 ]) Withmentioning

confidence: 99%

Growth rates of nucleation mode particles in Hyytiälä during 2003−2009: variation with particle size, season, data analysis method and ambient conditions

et al. 2011

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Abstract. The condensational growth rate of aerosol particles formed in atmospheric new particle formation events is one of the most important factors influencing the lifetime of these particles and their ability to become climatically relevant. Diameter growth rates (GR) of nucleation mode particles were studied based on almost 7 yr of data measured during the years 2003-2009 at a boreal forest measurement station SMEAR II in Hyytiälä, Finland. The particle growth rates were estimated using particle size distributions measured with a Differential Mobility Particle Sizer (DMPS), a Balanced Scanning Mobility Analyzer (BSMA) and an Air Ion Spectrometer (AIS). Two GR analysis methods were tested. The particle growth rates were also compared to an extensive set of ambient meteorological parameters and trace gas concentrations to investigate the processes/constituents limiting the aerosol growth. The median growth rates of particles in the nucleation mode size ranges with diameters of 1.5-3 nm, 3-7 nm and 7-20 nm were 1.9 nm h −1 , 3.8 nm h −1 , and 4.3 nm h −1 , respectively. The median relative uncertainties in the growth rates due to the size distribution instrumentation in these size ranges were 25 %, 19 %, and 8 %, respectively. For the smallest particles (1.5-3 nm) the AIS data yielded on average higher growth rate values than the BSMA data, and higher growth rates were obtained from positively charged size distributions as compared with negatively charged particles. For particles larger than 3 nm in diameter no such systematic differences were found. For these particles the uncertainty in the growth rate related to Correspondence to: T. Yli-Juuti (taina.yli-juuti@helsinki.fi) the analysis method, with relative uncertainty of 16 %, was similar to that related to the instruments. The growth rates of 7-20 nm particles showed positive correlation with monoterpene concentrations and their oxidation rate by ozone. The oxidation rate by OH did not show a connection with GR. Our results indicate that the growth of nucleation mode particles in Hyytiälä is mainly limited by the concentrations of organic precursors.

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Ion production rate in a boreal forest based on ion, particle and radiation measurements

Cited by 133 publications

References 28 publications

Boundary layer nucleation as a source of new CCN in savannah environment

Boundary layer nucleation as a source of new CCN in savannah environment

The global aerosol-climate model ECHAM-HAM, version 2: sensitivity to improvements in process representations

Growth rates of nucleation mode particles in Hyytiälä during 2003−2009: variation with particle size, season, data analysis method and ambient conditions

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