Four years of continuous aerosol number size distribution measurements from the Arctic Climate Observatory in Tiksi, Russia, are analyzed. Tiksi is located in a region where in situ information on ...aerosol particle properties has not been previously available. Particle size distributions were measured with a differential mobility particle sizer (in the diameter range of 7–500 nm) and with an aerodynamic particle sizer (in the diameter range of 0.5–10 μm). Source region effects on particle modal features and number, and mass concentrations are presented for different seasons. The monthly median total aerosol number concentration in Tiksi ranges from 184 cm−3 in November to 724 cm−3 in July, with a local maximum in March of 481 cm−3. The total mass concentration has a distinct maximum in February–March of 1.72–2.38 μg m−3 and two minimums in June (0.42 μg m−3) and in September–October (0.36–0.57 μg m−3). These seasonal cycles in number and mass concentrations are related to isolated processes and phenomena such as Arctic haze in early spring, which increases accumulation and coarse-mode numbers, and secondary particle formation in spring and summer, which affects the nucleation and Aitken mode particle concentrations. Secondary particle formation was frequently observed in Tiksi and was shown to be slightly more common in marine, in comparison to continental, air flows. Particle formation rates were the highest in spring, while the particle growth rates peaked in summer. These results suggest two different origins for secondary particles, anthropogenic pollution being the important source in spring and biogenic emissions being significant in summer. The impact of temperature-dependent natural emissions on aerosol and cloud condensation nuclei numbers was significant: the increase in both the particle mass and the CCN (cloud condensation nuclei) number with temperature was found to be higher than in any previous study done over the boreal forest region. In addition to the precursor emissions of biogenic volatile organic compounds, the frequent Siberian forest fires, although far away, are suggested to play a role in Arctic aerosol composition during the warmest months. Five fire events were isolated based on clustering analysis, and the particle mass and cloud condensation nuclei number were shown to be somewhat affected by these events. In addition, during calm and cold months, aerosol concentrations were occasionally increased by local aerosol sources in trapping inversions. These results provide valuable information on interannual cycles and sources of Arctic aerosols.
Traditional techniques for measuring the mole fractions of greenhouse gases in the well-mixed atmosphere have required dry sample gas streams (dew point < −25 °C) to achieve the inter-laboratory ...compatibility goals set forth by the Global Atmosphere Watch programme of the World Meteorological Organisation (WMO/GAW) for carbon dioxide (±0.1 ppm in the Northern Hemisphere and ±0.05 ppm in the Southern Hemisphere) and methane (±2 ppb). Drying the sample gas to low levels of water vapour can be expensive, time-consuming, and/or problematic, especially at remote sites where access is difficult. Recent advances in optical measurement techniques, in particular cavity ring down spectroscopy, have led to the development of greenhouse gas analysers capable of simultaneous measurements of carbon dioxide, methane and water vapour. Unlike many older technologies, which can suffer from significant uncorrected interference from water vapour, these instruments permit accurate and precise greenhouse gas measurements that can meet the WMO/GAW inter-laboratory compatibility goals (WMO, 2011a) without drying the sample gas. In this paper, we present laboratory methodology for empirically deriving the water vapour correction factors, and we summarise a series of in-situ validation experiments comparing the measurements in humid gas streams to well-characterised dry-gas measurements. By using the manufacturer-supplied correction factors, the dry-mole fraction measurements have been demonstrated to be well within the GAW compatibility goals up to a water vapour concentration of at least 1%. By determining the correction factors for individual instruments once at the start of life, this water vapour concentration range can be extended to at least 2% over the life of the instrument, and if the correction factors are determined periodically over time, the evidence suggests that this range can be extended up to and even above 4% water vapour concentrations.
Secondary new particle formation affects atmospheric aerosol and cloud droplet numbers and thereby, the aerosol effects on climate. In this paper, the frequency of nucleation events and the ...associated particle formation and growth rates, along with their seasonal variation, was analysed based on over ten years of aerosol measurements conducted at the Pallas GAW station in northern Finland. The long-term measurements also allowed a detailed examination of factors possibly favouring or suppressing particle formation. Effects of meteorological parameters and air mass properties as well as vapour sources and sinks for particle formation frequency and event parameters were inspected. In addition, the potential of secondary particle formation to increase the concentration of cloud condensation nuclei (CCN) sized particles was examined. Findings from these long-term measurements confirmed previous observations: event frequency peaked in spring and the highest growth rates were observed in summer, affiliated with increased biogenic activity. Events were almost exclusively observed in marine air masses on sunny cloud-free days. A low vapour sink by the background particle population as well as an elevated sulphuric acid concentration were found to favour particle formation. These were also conditions taking place most likely in marine air masses. Inter-annual trend showed a minimum in event frequency in 2003, when also the smallest annual median of growth rate was observed. This gives further evidence of the importance and sensitivity of particle formation for the condensing vapour concentrations at Pallas site. The particle formation was observed to increase CCN80 (>80 nm particle number) concentrations especially in summer and autumn seasons when the growth rates were the highest. When the growing mode exceeded the selected 80 nm limit, on average in those cases, 211 ± 114% increase of CCN80 concentrations was observed.
Understanding the recent evolution of methane emissions in the Arctic is necessary to interpret the global methane cycle. Emissions are affected by significant uncertainties and are sensitive to ...climate change, leading to potential feedbacks. A polar version of the CHIMERE chemistry-transport model is used to simulate the evolution of tropospheric methane in the Arctic during 2012, including all known regional anthropogenic and natural sources, in particular freshwater emissions which are often overlooked in methane modelling. CHIMERE simulations are compared to atmospheric continuous observations at six measurement sites in the Arctic region. In winter, the Arctic is dominated by anthropogenic emissions; emissions from continental seepages and oceans, including from the East Siberian Arctic Shelf, can contribute significantly in more limited areas. In summer, emissions from wetland and freshwater sources dominate across the whole region. The model is able to reproduce the seasonality and synoptic variations of methane measured at the different sites. We find that all methane sources significantly affect the measurements at all stations at least at the synoptic scale, except for biomass burning. In particular, freshwater systems play a decisive part in summer, representing on average between 11 and 26 % of the simulated Arctic methane signal at the sites. This indicates the relevance of continuous observations to gain a mechanistic understanding of Arctic methane sources. Sensitivity tests reveal that the choice of the land-surface model used to prescribe wetland emissions can be critical in correctly representing methane mixing ratios. The closest agreement with the observations is reached when using the two wetland models which have emissions peaking in August–September, while all others reach their maximum in June–July. Such phasing provides an interesting constraint on wetland models which still have large uncertainties at present. Also testing different freshwater emission inventories leads to large differences in modelled methane. Attempts to include methane sinks (OH oxidation and soil uptake) reduced the model bias relative to observed atmospheric methane. The study illustrates how multiple sources, having different spatiotemporal dynamics and magnitudes, jointly influence the overall Arctic methane budget, and highlights ways towards further improved assessments.
Nitrous oxide (N₂O) fluxes were measured fortnightly to monthly with manual chambers in 2004-2008 and hourly with automatic chambers during the snow-free seasons of 2007 and 2008 in a sedge fen in ...northern Finland. The fluxes were generally low, varying from -45 to 37 μg N₂O-N m⁻² hour⁻¹ (negative fluxes indicating uptake of N₂O from the atmosphere into the soil) and showing large spatial and temporal variation. Slightly higher emissions were observed in winter than in summer. On an annual scale, the fen acted as a N₂O source. The annual balances showed a clear decreasing trend from 1.1 kg N ha⁻¹ year⁻¹ (= 12.2 μg N m⁻² hour⁻¹) in 2004 to zero balances in 2007 and 2008. Two potential reasons for the decreasing mean flux were (i) a decreasing atmospheric N deposition during the snow-free season, and (ii) a rising water-table level (WTL), which restricts the availability of oxygen in the peat and therefore favours the formation of molecular nitrogen (N₂) instead of N₂O by the denitrifying microbes. The measurements conducted with the automatic chambers during the snow-free season showed a positive exponential relationship between the N₂O flux and the temperature in 2008, but not in 2007. Similarly, a unimodal relationship with the WTL was found in 2008, with maximum fluxes observed when the WTL was about 4 cm above the fen surface. No diurnal variation in N₂O fluxes measured by automatic chambers was found. The fluxes measured by the manual or automatic chambers were similar in magnitude, but different in their temporal pattern. The daily N₂O concentration at a depth of 0.15 m in the peat was always lower than the ambient atmospheric concentration, indicating that at this depth the atmospheric N₂O was consumed. Together with the observed negative flux rates this suggests that microbial N₂ production is a significant part of the N cycle in this fen.
Aerosol equivalent black carbon (BC
e) was measured at five different background stations in Finland, with the longest data set from Hyytiälä, December 2004–December 2008. Measurements were conducted ...either with an aethalometer or a Multi-Angle Absorption Photometer, MAAP. Measured black carbon concentrations were highest in Virolahti in southeastern Finland, with annual averages ranging from 385 to 460 ng m
−3, followed by Hyytiälä (250–370 ng m
−3), Utö (230–270 ng m
−3), Puijo (225–230 ng m
−3), and Pallastunturi (60–70 ng m
−3) in northern Finland. The BC
e fractions of measured PM
2.5 concentrations were generally between 5 and 10%, with highest fractions at Virolahti close to the Eastern border. At all the stations, the highest concentrations were observed during the spring and the winter, and the lowest concentrations during the summer. The seasonal cycle could generally be attributed to the reaching of long-range-transported black carbon. Additional reasons were increasing domestic wood burning and reduced boundary-layer height during winter, and a more effective vertical mixing during summer. The highest concentrations for each station occurred with southerly winds, and on the basis of trajectory analyses, the source areas of BC
e resided mostly in Central and Eastern Europe. Occasionally the long-range-transported BC
e concentrations were elevated for short periods to fulfill the characteristics of pollution episodes. From these episodes, about 62% were a result of non-fire anthropogenic sources and 36% due to open biomass burning sources. Episodes from the biomass burning sources were most often observed during the spring.
► Long term black carbon measurements reported in and close to the Arctic. ► Trans-boundary transport a major source of black carbon in clean areas. ► Open biomass burning a reason for transported black carbon in Northern Europe.
Previous studies have noted that aerosols originating from the polluted Indo-Gangetic plains can reach high altitudes at the Indian Himalayas and thereby have an effect on the south Asian monsoon. ...Here we examine the transport of pollutions by comparing aerosol properties from a Himalayan foothill measurement site and a site at the Indo-Gangetic plains. Gual Pahari is a polluted semi-urban background measurement site at the Indo-Gangetic plains close to New Delhi and Mukteshwar is a relatively clean background measurement site at the foothills of the Himalayas about 270 km NE from Gual Pahari and about 2 km above the nearby plains. The data set has more than two years of simultaneous measurements including meteorological parameters and aerosol mass concentrations. Modeled backward trajectories and Planetary Boundary Layer (PBL) heights are also used to examine the origin or air masses and the extent of the vertical mixing. The comparison shows that aerosol concentrations at the foothill site are correlated with the average PBL height. Together with the favorable synoptic scale circulation, this suggests a contribution of air mass transport from the plains.
•We compare aerosol properties from Himalayan foothills and Indo-Gangetic plains.•The data set contains more than two years of simultaneous measurements.•Aerosols are transported from the plains to the Himalayan foothills.•Boundary layer dynamics can explain the observed aerosol concentrations.
Background:
Patient selection for either total knee arthroplasty or unicompartmental knee arthroplasty remains controversial. The latter has several reported advantages over total knee arthroplasty, ...but it also appears to have significant drawbacks in terms of revision rates.
Aims:
This study aimed to determine the influence of the preoperative degree of osteoarthritis on the risk of reoperation following unicompartmental knee arthroplasty.
Methods:
Surgery was carried out on 294 knees in 241 patients between 2001 and 2012 at a single institute, using cemented Oxford phase III unicompartmental knee arthroplasty. The mean age at the time of operation was 67 years, and the mean follow-up time was 8.7 years.
Results and Conclusion:
The knees with a preoperative Kellgren–Lawrence grade of 0–2 osteoarthritis had a higher risk of reoperation than those with a Kellgren–Lawrence grade of 3–4 (odds ratio = 1.89; 95% confidence interval, 1.03–3.45; p = 0.04). In addition, the knees with a medial joint space width of more than 1 mm or a high medial/lateral joint space width ratio had an increased risk of reoperation. In conclusion, we suggest that unicompartmental knee arthroplasty should only be performed in cases showing severe osteoarthritis in preoperative radiographs, with medial bone-on-bone contact, and a medial/lateral ratio of <20%.
Recent studies have shown very high frequencies of atmospheric new particle formation in different environments in South Africa. Our aim here was to investigate the causes for two or three ...consecutive daytime nucleation events, followed by subsequent particle growth during the same day. We analysed 108 and 31 such days observed in a polluted industrial and moderately polluted rural environments, respectively, in South Africa. The analysis was based on two years of measurements at each site. After rejecting the days having notable changes in the air mass origin or local wind direction, i.e. two major reasons for observed multiple nucleation events, we were able to investigate other factors causing this phenomenon. Clouds were present during, or in between most of the analysed multiple particle formation events. Therefore, some of these events may have been single events, interrupted somehow by the presence of clouds. From further analysis, we propose that the first nucleation and growth event of the day was often associated with the mixing of a residual air layer rich in SO2 (oxidized to sulphuric acid) into the shallow surface-coupled layer. The second nucleation and growth event of the day usually started before midday and was sometimes associated with renewed SO2 emissions from industrial origin. However, it was also evident that vapours other than sulphuric acid were required for the particle growth during both events. This was especially the case when two simultaneously growing particle modes were observed. Based on our analysis, we conclude that the relative contributions of estimated H2SO4 and other vapours on the first and second nucleation and growth events of the day varied from day to day, depending on anthropogenic and natural emissions, as well as atmospheric conditions.
We investigate the sensitivity of future spaceborne lidar measurements to changes in surface methane emissions. We use surface methane observations from nine European ground stations and a Lagrangian ...transport model to infer surface methane emissions for 2010. Our inversion shows the strongest emissions from the Netherlands, the coal mines in Upper Silesia, Poland, and wetlands in southern Finland. The simulated methane surface concentrations capture at least half of the daily variability in the observations, suggesting that the transport model is correctly simulating the regional transport pathways over Europe. With this tool we can test whether proposed methane lidar instruments will be sensitive to changes in surface emissions. We show that future lidar instruments should be able to detect a 50% reduction in methane emissions from the Netherlands and Germany, at least during summer.
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