Explore the vast range of titles available.

In this study the high-frequency loss of carbon dioxide (CO2) and water vapor (H2O) fluxes, measured by a closed-path eddy covariance system, were studied, and the related correction factors through the cospectral transfer function method were calculated. As already reported by other studies, it was found that the age of the sampling tube is a relevant factor to consider when estimating the spectral correction of water vapor fluxes. Moreover, a time-dependent relationship between the characteristic time constant (or response time) for water vapor and the ambient relative humidity was disclosed. Such dependence is negligible when the sampling tube is new, but it becomes important already when the tube is only 1 yr old and increases with the age of the tube. With a new sampling tube, the correction of water vapor flux measurements over a Scots pine forest in Hyytiälä, Finland, amounted on average to 7%. After 4 yr the correction increased strongly, ranging from 10%–15% during the summer to 30%–40% in wintertime, when the relative humidity is typically high. For this site the effective correction improved the long-term energy and water balance. Results suggest that the relative humidity effect on high-frequency loss of water vapor flux should be taken into account and that the effective transfer function should be estimated experimentally at least once per year. On the other hand, this high correction can be avoided by a correct choice and periodic maintenance of the eddy covariance system tube, for example, by cleaning or changing it at least once per year.

The metallurgical industry in the Kola Peninsula, north-west Russia, form, after Norilsk, Siberia, the second largest source of air pollution in the Arctic and subarctic domain. Sulfur dioxide (SO2) emissions from the ore smelters are transported to wide areas, including Finnish Lapland. We performed investigations on concentrations of SO2, aerosol precursor vapours, aerosol and ion cluster size distributions together with chemical composition measurements of freshly formed clusters at the SMEAR I station in Finnish Lapland relatively close (∼ 300 km) to the Kola Peninsula industrial sites during the winter 2019–2020. We show that highly concentrated SO2 from smelter emissions is converted to sulfuric acid (H2SO4) in sufficient concentrations to drive new particle formation hundreds of kilometres downwind from the emission sources, even at very low solar radiation intensities. Observed new particle formation is primarily initiated by H2SO4–ammonia (negative-)ion-induced nucleation. Particle growth to cloud condensation nuclei (CCN) sizes was concluded to result from sulfuric acid condensation. However, air mass advection had a large role in modifying aerosol size distributions, and other growth mechanisms and condensation of other compounds cannot be fully excluded. Our results demonstrate the dominance of SO2 emissions in controlling wintertime aerosol and CCN concentrations in the subarctic region with a heavily polluting industry.

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.

This work presents airborne observations of sub-3 nm particles in the lower troposphere and investigates new particle formation (NPF) within an evolving boundary layer (BL). We studied particle concentrations together with supporting gas and meteorological data inside the planetary BL over a boreal forest site in Hyytiälä, southern Finland. The analysed data were collected during three flight measurement campaigns: May-June 2015, August 2015 and April-May 2017, including 27 morning and 26 afternoon vertical profiles. As a platform for the instrumentation, we used a Cessna 172 aircraft. The analysed flight data were collected horizontally within a 30 km distance from SMEAR II in Hyytiälä and vertically from 100 m above ground level up to 2700 m. The number concentration of 1.5-3 nm particles was observed to be, on average, the highest near the forest canopy top and to decrease with increasing altitude during the mornings of NPF event days. This indicates that the precursor vapours emitted by the forest play a key role in NPF in Hyytiälä. During daytime, newly formed particles were observed to grow in size and the particle population became more homogenous within the well-mixed BL in the afternoon. During undefined days with respect to NPF, we also detected an increase in concentration of 1.5-3 nm particles in the morning but not their growth in size, which indicates an interrupted NPF process during these undefined days. Vertical mixing was typically stronger during the NPF event days than during the undefined or non-event days. The results shed light on the connection between boundary layer dynamics and NPF.

New particle formation (NPF) events substantially contribute to the number concentration of atmospheric particles and cloud condensation nuclei (CCN) which can further influence radiative balance and Earth's climate. Many short-term studies have found that sulfuric acid (H2 SO4) and highly oxygenated organic molecules (HOM) are critical compounds in the early steps of NPF. However, it is not fully understood how NPF intensity and frequency respond to global warming and declining anthropogenic sulfur dioxide (SO2) emissions, affecting HOM and H2 SO4 formation, respectively. Here, we report the results of long-term (over 20 years) datasets collected at the Station for Measuring Ecosystem-Atmosphere Relations (SMEAR) II (Hyytiälä, Finland). Owing to the significant contribution of HOM in the initial and subsequent particle formation and growth, we have derived a HOM proxy for conducting the long-term trend analysis. Measurement results together with modelled proxies reveal the declining trends of SO2, H2 SO4, Condensation Sink (CS), NPF frequency and particle formation rate (J3) along with increasing trends of monoterpenes and HOM.

Smart-SMEAR is an interface to visualize the data measured at the SMEAR II station in Hyytiälä, Finland. It is designed to be an additional tool for data mining and a simple tool for working together with trace gas and aerosol data, meteorological parameters and air mass back-trajectories, including numerous point sources. The web tool acts as an interface to the station database which can be reached with only few mouse clicks. The tool provides an overview of such a complicated dataset. The database contains all the data from the start of continuous SMEAR II measurements in 1996 until today. Here, we present also some examples of how to use Smart-SMEAR. We present examples of one typical atmospheric nucleation event day, one local pollution event with low photochemical activity, and one long-range-transport pollution day coupled with local pollution events with strong solar radiation. Smart-SMEAR, together with its search engine Smart-Search, has proven to be an efficient tool for studying atmospheric chemistry and atmospheric aerosol dynamics.

New particle formation (NPF) events substantially contribute to the number concentration of atmospheric particles and cloud condensation nuclei (CCN) which can further influence radiative balance and Earth's climate. Many short-term studies have found that sulfuric acid (H2SO4) and highly oxygenated organic molecules (HOM) are critical compounds in the early steps of NPF. However, it is not fully understood how NPF intensity and frequency respond to global warming and declining anthropogenic sulfur dioxide (SO2) emissions, affecting HOM and H2SO4 formation, respectively. Here, we report the results of long-term (over 20 years) datasets collected at the Station for Measuring Ecosystem-Atmosphere Relations (SMEAR) II (Hyytiälä, Finland). Owing to the significant contribution of HOM in the initial and subsequent particle formation and growth, we have derived a HOM proxy for conducting the long-term trend analysis. Measurement results together with modelled proxies reveal the declining trends of SO2, H2SO4, Condensation Sink (CS), NPF frequency and particle formation rate (J3) along with increasing trends of monoterpenes and HOM.

In a changing climate, it is critical to reduce emissions of carbon dioxide and other greenhouse gases. At the same time, we need to remove carbon dioxide from the atmosphere. In addition, it is important to make other radiative forcing components, such as those due to changes in atmospheric aerosol loadings, clouds and albedo, to counteract the warming effects of greenhouse gases. An important way to reduce warming is the removal of CO2 from atmosphere by ecosystems, which act as carbon sinks and storages. However, ecosystems influence also other radiative forcing components, yet the full potential of different ecosystems to mitigate climate warming is challenging to compare. Here we propose a novel concept (CarbonSink+ Potential) to compare ecosystems in terms of their carbon uptake and aerosol production capacity. In our approach, we utilize the regional aerosol formation measured at the SMEAR II station in Hyytiälä, southern Finland, together with locally measured negative ion concentrations at various ecosystems within the region (forest, peatland and grassland). The local ion concentrations are measured in the size range of 2.0‒2.3 nm that indicates aerosol formation within a source area of roughly similar size as that of carbon sink measurements. The results show that, among the studied boreal ecosystems and per surface area, the pristine peatland has the lowest aerosol production and carbon sink, so this ecosystem is likely to have the smallest potential to contribute to climatic cooling (per land area). Forest (on mineral soil) has the highest carbon sink and grassland (on mineral soil) has the highest potential for aerosol production. This means, for example, that the relative contribution of grassland to climate mitigation is more important than when considering only the carbon sink.

We investigated the concentrations and vertical profiles of ozone over a 20-year period (1996–2016) at the SMEAR II station in southern Finland. Our results showed that the typical daily median ozone concentrations were in the range of 20–50 ppb with clear diurnal and annual patterns. In general, the profile of ozone concentrations illustrated an increase as a function of heights. The main aim of our study was to address the frequency and strength of ozone depletion events at this boreal forest site. We observed more than a thousand of 10 min periods at 4.2 m, with ozone concentrations below 10 ppb, and a few tens of cases with ozone concentrations below 2 ppb. Among these observations, a number of ozone depletion events that lasted for more than 3 h were identified, and they occurred mainly in autumn and winter months. The low ozone concentrations were likely related to the formation of a low mixing layer under the conditions of low temperatures, low wind speeds, high relative humidities and limited intensity of solar radiation.

This work presents airborne observations of sub-3 nm particles in the lower troposphere and investigates new particle formation (NPF) within an evolving boundary layer (BL). We studied particle concentrations together with supporting gas and meteorological data inside the planetary BL over a boreal forest site in Hyytiälä, southern Finland. The analysed data were collected during three flight measurement campaigns: May–June 2015, August 2015 and April–May 2017, including 27 morning and 26 afternoon vertical profiles. As a platform for the instrumentation, we used a Cessna 172 aircraft. The analysed flight data were collected horizontally within a 30 km distance from SMEAR II in Hyytiälä and vertically from 100 m above ground level up to 2700 m. The number concentration of 1.5–3 nm particles was observed to be, on average, the highest near the forest canopy top and to decrease with increasing altitude during the mornings of NPF event days. This indicates that the precursor vapours emitted by the forest play a key role in NPF in Hyytiälä. During daytime, newly formed particles were observed to grow in size and the particle population became more homogenous within the well-mixed BL in the afternoon. During undefined days with respect to NPF, we also detected an increase in concentration of 1.5–3 nm particles in the morning but not their growth in size, which indicates an interrupted NPF process during these undefined days. Vertical mixing was typically stronger during the NPF event days than during the undefined or non-event days. The results shed light on the connection between boundary layer dynamics and NPF.