[Show abstract][Hide abstract] ABSTRACT: Oxidation products of monoterpenes and isoprene have a major influence on the global secondary organic aerosol (SOA) burden and the production of atmospheric nanoparticles and cloud condensation nuclei (CCN). Here, we investigate the formation of extremely low volatility organic compounds (ELVOC) from O3 and OH radical oxidation of several monoterpenes and isoprene in a series of laboratory experiments. We show that ELVOC from all precursors are formed within the first minute after the initial attack of an oxidant. We demonstrate that under atmospherically relevant concentrations, species with an endocyclic double bond efficiently produce ELVOC from ozonolysis, whereas the yields from OH radical-initiated reactions are smaller. If the double bond is exocyclic or the compound itself is acyclic, ozonolysis produces less ELVOC and the role of the OH radical-initiated ELVOC formation is increased. Isoprene oxidation produces marginal quantities of ELVOC regardless of the oxidant. Implementing our laboratory findings into a global modeling framework shows that biogenic SOA formation in general, and ELVOC in particular, play crucial roles in atmospheric CCN production. Monoterpene oxidation products enhance atmospheric new particle formation and growth in most continental regions, thereby increasing CCN concentrations, especially at high values of cloud supersaturation. Isoprene-derived SOA tends to suppress atmospheric new particle formation, yet it assists the growth of sub-CCN-size primary particles to CCN. Taking into account compound specific monoterpene emissions has a moderate effect on the modeled global CCN budget.
Proceedings of the National Academy of Sciences 05/2015; 112(23). DOI:10.1073/pnas.1423977112 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Understanding new particle formation and their subsequent growth in the troposphere has a critical impact on our ability to predict atmospheric composition and global climate change. High pre-existing particle loadings have been thought to suppress the formation of new atmospheric aerosol particles due to high condensation and coagulation sinks. Here, based on field measurements at a mountain site in South China, we report, for the first time, in situ observational evidence on new particle formation and growth in remote ambient atmosphere during heavy dust episodes mixed with anthropogenic pollution. Both the formation and growth rates of particles in the diameter range 15-50 nm were enhanced during the dust episodes, indicating the influence of photo-induced, dust surface-mediated reactions and resulting condensable vapor production. This study provides unique in situ observations of heterogeneous photochemical processes inducing new particle formation and growth in the real atmosphere, and suggests an unexpected impact of mineral dust on climate and atmospheric chemistry.
[Show abstract][Hide abstract] ABSTRACT: Biomass burning emissions from intensive wildfires in eastern Europe were observed in Finland in the spring of 2006 and in the late of summers 2006 and 2010. The smoke plumes were detected at three ground-measurement stations around Finland and in the lower troposphere after long-range transport from fire areas. The vertical extent of the smoke was estimated by flight measurements over southern Finland and the measurements were compared with CALIPSO satellite data from 29 July 2010. The history of the arriving air masses was analysed by using backward trajectories and MODIS fire detections. The smoke plumes had elevated concentrations of aerosol particle number, black carbon, CO, CO2, SO2, O-3 and NOx, and the differences as compared with the background air were clear. The smoke was observed to be highly scattering, with a single-scattering albedo of 0.96 +/- 0.01. The median particle size was 60%-250% larger during the plume days than during July August on average, and the growth of smoke particles was observed even after long-range transport of several hundreds of kilometres.
Boreal Environment Research 09/2014; 19(B, SI):275-292. · 1.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: New-particle formation (NPF) is globally an important source of climatically-relevant atmospheric aerosols. Here we explore the inter-annual variability and trends in sources and sinks of atmospheric nanoparticles in a boreal forest environment. We look into the precursor vapors leading to the aerosol formation, NPF frequency, as well as the formation and growth rates of the freshly-formed particles. The analysis is based on 16 years of data acquired from the Station for Measuring Ecosystem Atmosphere Relations (SMEAR II) in Hyytiala, Finland. The results indicate that the probability of NPF is connected to both air mass origin, explaining a large part of the year-to-year variability in the number of NPF events, and concentrations of low-volatile vapours. The probability of NPF increases with increasing gaseous sulphuric acid concentrations, but even better association is found between the NPF probability and product of sulphuric acid and low-volatile organic vapour (proxy) concentrations. While the concentrations of both sulphuric acid (evaluated by proxy) and sulphuric-acid precursor sulphur dioxide decreased over the 16-year measurement period, the new-particle formation and growth rates slightly increased. On the other hand, the proxy concentrations of oxidized organics increased in all seasons except in winter. The contribution of sulphuric acid to the particle growth was minor, and the growth rate had a clear connection with the ambient temperature due to higher emissions of biogenic volatile organic compounds at higher temperatures. For a given sulphuric acid concentration evaluated by proxy, particle formation rates tended to be higher at higher temperatures.
Boreal Environment Research 09/2014; 19(B, SI):191-214. · 1.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The subject of the study was the effect of monoterpene oxidation on the growth of particles during new-particle formation (NPF) events at the SMEAR II measurement station in Hyytiala, southern Finland, during 2006-2011. The nighttime oxidation capacity, i.e. how readily the atmosphere can oxidize monoterpenes, was found to be dominated by the nitrate radical, whereas the daytime oxidation capacity was mainly dominated by ozone. The mean lifetimes of monoterpenes ranged from about one hour to several hours, depending on the time of year and day. A strong link was found between the growth rate of particles of 7-20 nm in diameter during the NPF events and monoterpene oxidation by ozone during the preceding night. Our findings suggest that during nighttime a build-up of primarily oxidized monoterpenes in the atmosphere occurs, and that these compounds can be oxidized by the hydroxyl radical after sunrise, promoting the particle growth.
Boreal Environment Research 09/2014; 19(B, SI):293-310. · 1.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Feedbacks mechanisms are essential components of our climate system, as they either increase or decrease changes in climate-related quantities in the presence of external forcings. In this work, we provide the first quantitative estimate regarding the terrestrial climate feedback loop connecting the increasing atmospheric carbon dioxide concentration, changes in gross primary production (GPP) associated with the carbon uptake, organic aerosol formation in the atmosphere, and transfer of both diffuse and global radiation. Our approach was to combine process-level understanding with comprehensive, long-term field measurement data set collected from a boreal forest site in southern Finland. Our best estimate of the gain in GPP resulting from the feedback is 1.3 (range 1.02-1.5), which is larger than the gains of the few atmospheric chemistry-climate feedbacks estimated using large-scale models. Our analysis demonstrates the power of using comprehensive field measurements in investigating the complicated couplings between the biosphere and atmosphere on one hand, and the need for complementary approaches relying on the combination of field data, satellite observations model simulations on the other hand.
Boreal Environment Research 09/2014; 19(B, SI):122-131. · 1.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Forests emit large quantities of volatile organic compounds (VOCs) to the atmosphere. Their condensable oxidation products can form secondary organic aerosol, a significant and ubiquitous component of atmospheric aerosol, which is known to affect the Earth's radiation balance by scattering solar radiation and by acting as cloud condensation nuclei. The quantitative assessment of such climate effects remains hampered by a number of factors, including an incomplete understanding of how biogenic VOCs contribute to the formation of atmospheric secondary organic aerosol. The growth of newly formed particles from sizes of less than three nanometres up to the sizes of cloud condensation nuclei (about one hundred nanometres) in many continental ecosystems requires abundant, essentially non-volatile organic vapours, but the sources and compositions of such vapours remain unknown. Here we investigate the oxidation of VOCs, in particular the terpene α-pinene, under atmospherically relevant conditions in chamber experiments. We find that a direct pathway leads from several biogenic VOCs, such as monoterpenes, to the formation of large amounts of extremely low-volatility vapours. These vapours form at significant mass yield in the gas phase and condense irreversibly onto aerosol surfaces to produce secondary organic aerosol, helping to explain the discrepancy between the observed atmospheric burden of secondary organic aerosol and that reported by many model studies. We further demonstrate how these low-volatility vapours can enhance, or even dominate, the formation and growth of aerosol particles over forested regions, providing a missing link between biogenic VOCs and their conversion to aerosol particles. Our findings could help to improve assessments of biosphere-aerosol-climate feedback mechanisms, and the air quality and climate effects of biogenic emissions generally.
[Show abstract][Hide abstract] ABSTRACT: We used a monoterpene volume mixing ratio dataset measured from 12 June 2006 to 24 September 2007 and from 1 June 2008 to 3 March 2009 at the SMEAR II station to quantify the magnitude of anthropogenic monoterpene emissions aside from biogenic origins, to examine the anthropogenic sources, and to look at other associated pollutants. We discuss the relations between increased monoterpene mixing ratios and particle concentrations. We also characterize chemical properties of aerosol particles during two monoterpene pollution episodes in case studies. Out of 580 days analyzed, anthropogenic monoterpene pollution episodes were found on 341 (58.8%) days. The average monoterpene mixing ratio increased from 0.19 to 0.26 ppbv due to the presence of anthropogenic monoterpenes, which is equal to an increase of 36.8%. The observed anthropogenic monoterpenes were mostly from the Korkeakoski sawmill. Other gas pollutants might occasionally be emitted during the episodes, but did not show clear association with anthropogenic monoterpenes. Aerosol particle concentrations substantially increased during episodes, and monoterpene mixing ratios showed strong connections with Aitken mode particles both in number and volume concentrations. Particles associated with monoterpene episodes reached a CCN (cloud concentration nucleus) size. The chemical characterizations of aerosol particles in case studies show that the increase in aerosol particle mass was mainly from secondary organic aerosol.
Boreal Environment Research 08/2013; 16:288-303. · 1.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Atmospheric fine particle black carbon (BC) was measured close to downtown of Helsinki, during November 1996–June 1997. The average BC concentrations were 1.5 μg m−3 for working days, 1.2 μg m−3 for Saturdays, and about 1 μg m−3 for Sundays and public holidays. The overall average BC concentration was equal to 1.38 μg m−3 and its average contribution to fine particle mass equal to 19%. On working days BC concentrations showed a clear diurnal variation with the highest hourly average values occurring during the morning (2.7 μg m−3) and evening (1.9 μg m−3) rush hours. Contribution of the long-range transport to the BC was estimated to be on average about 0.4 μg m−3, which is believed to represent the average regional background over southern Finland. However, this transport was very different from different geographical regions: from the densely populated areas of East- and Central-Europe it was about 0.8 μg m−3, while in northerly and northwesterly air masses it was only about 0.15 μg m−3. Local traffic was by far the most important local BC source contributing about 63, 54 and 44% on working days, Saturdays and Sundays, respectively. Other local sources were largely masked by the traffic and their contribution was estimated roughly to be of the order of 10%. The rest of BC was attributed to long-range transport.
[Show abstract][Hide abstract] ABSTRACT: The chemistry of sea-salt particles was investigated in summer Antarctica at a site about 150 km from the open ocean. Aerosol samples were collected using a low-pressure impactor which divides particles into 12 size fractions over the aerodynamic particle diameter range 0.045–15 μm. Measured sea-salt particle concentrations were clearly lower than concentrations typically observed at coastal Antarctica. The mass size distribution of sea salt was tri-modal with a submicron mode centering at 0.5–1 μm and two supermicron modes centering slightly below 2 μm and somewhere between 2 and 10 μm, respectively. On average more than 70% of sea salt was found in the supermicron size range, the lower supermicron mode being usually the dominant. Sea-salt particles displayed a large chloride loss with respect to the bulk sea water. The average loss percentage was more than 90% for submicron particles and decreased to about 50% for particles larger than 3 μm in diameter. The primary ions causing the chloride loss were sulfate, nitrate, and methanesulfonate (MSA). The aerosol MSA to non-sea-salt sulfate weight ratio seemed to have been increased by the presence of sea-salt particles. Particulate nitrate was associated strongly with sea salt, the most likely formation pathway being the interaction of nitric acid or some other gaseous nitrogen compounds with these particles in the Antarctic atmosphere.
[Show abstract][Hide abstract] ABSTRACT: Atmospheric aerosol particles influence the climate system directly by
scattering and absorbing solar radiation, and indirectly by acting as
cloud condensation nuclei. Apart from black carbon aerosol, aerosols
cause a negative radiative forcing at the top of the atmosphere and
substantially mitigate the warming caused by greenhouse gases. In the
future, tightening of controls on anthropogenic aerosol and precursor
vapour emissions to achieve higher air quality may weaken this
beneficial effect. Natural aerosols, too, might affect future warming.
Here we analyse long-term observations of concentrations and
compositions of aerosol particles and their biogenic precursor vapours
in continental mid- and high-latitude environments. We use measurements
of particle number size distribution together with boundary layer
heights derived from reanalysis data to show that the boundary layer
burden of cloud condensation nuclei increases exponentially with
temperature. Our results confirm a negative feedback mechanism between
the continental biosphere, aerosols and climate: aerosol cooling effects
are strengthened by rising biogenic organic vapour emissions in response
to warming, which in turn enhance condensation on particles and their
growth to the size of cloud condensation nuclei. This natural growth
mechanism produces roughly 50% of particles at the size of cloud
condensation nuclei across Europe. We conclude that biosphere-atmosphere
interactions are crucial for aerosol climate effects and can
significantly influence the effects of anthropogenic aerosol emission
controls, both on climate and air quality.
[Show abstract][Hide abstract] ABSTRACT: The use of the first nucleation theorem on atmospheric particle
formation events is studied under simulated conditions trying to
represent the varying conditions of a typical field campaign. The
aerosol dynamics model UHMA is used to produce synthesized DMPS data,
which are analyzed using typical techniques to obtain particle formation
rates, and with back calculation, nucleation rates. The results show
that under conditions that cause time and/or size dependent growth
rates, standard techniques can result in serious errors when estimating
nucleation rates. In addition, the validity of obtaining information
about nucleation mechanisms by plotting data at different conditions
into a single log J vs. log [H2SO4] plot to deduce
mechanisms based on slope values, seems questionable.
[Show abstract][Hide abstract] ABSTRACT: Sulfur emissions from the Kola Peninsula smelter industry have been
decreasing over the past two decades. We investigated the effect of this
to new particle formation at SMEAR I station in Eastern Lapland,
Finland, using long-term measurements of trace gases and aerosol size
distributions. We show that the number of events per year has decreased
and can be linked with the decreasing sulfur emissions from Kola.
[Show abstract][Hide abstract] ABSTRACT: Long-term atmospheric dataset including aerosol field measurement and
back trajectories was used to investigate the impact of temperature to
the production of secondary organic aerosols from biogenic monoterpene
emissions among boreal forest area. Temperature was equally divided into
five bins ranging from 0 to 20 °C in this study, and all parameters
were classified into the corresponding temperature bins. Own results
suggest that increase in temperature causing an increase in MT emission
will not necessarily result in the increase of secondary organic aerosol
production. Therefore, to predict the aerosol production potential in
the future with rising temperature, a simple extrapolation cannot be
applied between the total aerosol production and temperature. In
addition, the climatic feedback due to the increase in aerosol
production to buffer the warming over boreal forest area may be less
significant as previously expected.
[Show abstract][Hide abstract] ABSTRACT: Measured aerosol size distributions from three measurement stations and
modeled air mass trajectory data were combined to study aerosol dynamics
in the boreal forest zone in Northern Scandinavia. Three approaches were
used: investigation of new particle formation events, analysis of air
masses arriving from ocean to continent, and study of changes in the
aerosol size distributions when air masses travel from one measurement
site to another. The statistical analysis of air masses travelling
either from the Atlantic Ocean to measurement sites or from one site to
another showed that on average the condensational growth was present
during the summer season, and it was not restricted only to the days
when evident new particle formation was observed. The rate of this
average apparent growth of particle diameter was 3-7 times smaller than
the growth rate of nucleation mode particles during the new particle
[Show abstract][Hide abstract] ABSTRACT: A comprehensive suite of chemical ionization mass spectrometers (CIMS)
were deployed for chamber studies of monoterpene oxidation. The CIMS
instruments were able to detect several different groups of compounds
ranging from volatile to practically non-volatile. The compound groups
showed very different behavior and correlations with aerosol number and
mass. Results suggest that major gas phase contributors are not
considered in current models.
[Show abstract][Hide abstract] ABSTRACT: The role of ion-ion recombination in new particle formation is still
unclear. In this work, we present a new method to estimate the size
distribution of recombination products from atmospheric measurements. By
applying our method to size distributions of charged and neutral
clusters measured in Hyytiälä, Finland, we show that only a
minor fraction of all sub-2nm neutral clusters originate from ion-ion
recombination in boreal forest conditions.
[Show abstract][Hide abstract] ABSTRACT: Ambient aerosol CCN and hygroscopic properties were measured with a
size-segregated CCNc in a boreal environment of Southern Finland at the
SMEAR II station since February 2009. The overall median critical
diameter Dc for CCN activation is reported at 75 nm, exhibiting a clear
maximum in February and a minimum in July. The overall median aerosol
hygroscopicity parameter κ is reported at 0.22, indicating that
ambient aerosol in Hyytiälä is less hygroscopic than the
global continental and European continental averages. It is, however,
more hygroscopic than ambient aerosol in an Amazon rainforest, the
European high alpine site or the mountainous forest. The low
hygroscopicity in the boreal forest is attributed to a large organic
fraction present in the aerosol mass comparative to other locations
within Europe. Aerosol mass spectrometer (AMS) data were used to
demonstrate a positive correlation between κ and sulphate and
ammonia, and a negative correlation between κ and the organic mass
fraction. No distinguishable effect of atmospheric new particle
formation (NPF) on Dc and κ was observed. Ambient aerosol was
found to be internally mixed in the summer, and externally mixed during
the rest of the year.
[Show abstract][Hide abstract] ABSTRACT: Atmospheric new particle formation is the dominant source of aerosol
particles in the global atmosphere and an important player in aerosol
climatic effects. The key steps of this process occur in the sub-2 nm
size range. We have recently shown that at a lower-troposphere site
(Hyytiälä, Southern Finland) with abundant biogenic emissions
and moderate anthropogenic influence, based on comprehensive
observations of atmospheric clusters in the size range of 1-2 nm
mobility diameter, there are significant differences between neutral and
charged cluster properties. The differences are with respect to cluster
size and chemical composition, and whether the observations were made in
background conditions or during periods of active aerosol formation.
According to our results, sub-2 nm clusters were always present and
cluster concentrations were dominated by neutral ones in all sizes and
almost all the time, indicating that cluster formation and their
subsequent growth i.e. atmospheric aerosol formation were dominated by