Ground-level Air Research Articles

Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints

According to the 'Faint Young Sun' paradox, during the late Archaean eon a Sun approximately 20% dimmer warmed the early Earth such that it had liquid water and a clement climate. Explanations for this phenomenon have invoked a denser atmosphere that provided warmth by nitrogen pressure broadening or enhanced greenhouse gas concentrations. Such solutions are allowed by geochemical studies and numerical investigations that place approximate concentration limits on Archaean atmospheric gases, including methane, carbon dioxide and oxygen. But no field data constraining ground-level air density and barometric pressure have been reported, leaving the plausibility of these various hypotheses in doubt. Here we show that raindrop imprints in tuffs of the Ventersdorp Supergroup, South Africa, constrain surface air density 2.7 billion years ago to less than twice modern levels. We interpret the raindrop fossils using experiments in which water droplets of known size fall at terminal velocity into fresh and weathered volcanic ash, thus defining a relationship between imprint size and raindrop impact momentum. Fragmentation following raindrop flattening limits raindrop size to a maximum value independent of air density, whereas raindrop terminal velocity varies as the inverse of the square root of air density. If the Archaean raindrops reached the modern maximum measured size, air density must have been less than 2.3 kg m(-3), compared to today's 1.2 kg m(-3), but because such drops rarely occur, air density was more probably below 1.3 kg m(-3). The upper estimate for air density renders the pressure broadening explanation possible, but it is improbable under the likely lower estimates. Our results also disallow the extreme CO(2) levels required for hot Archaean climates.

Assessment of atmospheric impacts of biomass open burning in Kalimantan, Borneo during 2004

Biomass burning from the combustion of agricultural wastes and forest materials is one of the major sources of air pollution. The objective of the study is to investigate the major contribution of the biomass open burning events in the island of Borneo, Indonesia to the degradation of air quality in equatorial Southeast Asia. A total of 10173 active fire counts were detected by the MODIS Aqua satellite during August 2004, and consequently, elevated the PM10 concentration levels at six air quality stations in the state of Sarawak, in east Malaysia, which is located in northwestern Borneo. The PM10 concentrations measured on a daily basis were above the 50μgm−3 criteria as stipulated by the World Health Organization Air Quality Guidelines for most of the month, and exceeded the 24-h Recommended Malaysian Air Quality Guidelines of 150μgm−3 on three separate periods from the 13th to the 30th August 2004. The average correlation between the ground level PM10 concentrations and the satellite derived aerosol optical depth (AOD) of 0.3 at several ground level air quality stations, implied the moderate relationship between the aerosols over the depth of the entire column of atmosphere and the ground level suspended particulate matter. Multiple regression for meteorological parameters such as rainfall, windspeed, visibility, mean temperature, relative humidity at two stations in Sarawak and active fire counts that were located near the centre of fire activities were only able to explain for 61% of the total variation in the AOD.The trajectory analysis of the low level mesoscale meteorological conditions simulated by the TAPM model illustrated the influence of the sea and land breezes within the lowest part of the planetary boundary layer, embedded within the prevailing monsoonal southwesterlies, in circulating the aged and new air particles within Sarawak.

Resuspension processes controll variations of 137Cs activity concentrations in the ground-level air

The 137Cs activity concentration in the surface air between 1977 and 2007 was decreasing with an ecological half-life of 3.4 years, however, during 2007–2010 the yearly averaged 137Cs activity concentrations were almost constant. The increased atmospheric 137Cs and 40K levels observed during the winter may be due to surface soil resuspension and radionuclide transport by winds, particularly from open agricultural areas, as confirmed by high correlation coefficient between 137Cs and 40K atmospheric levels (R = 0.84), and similar 137Cs/40K activity ratios in aerosols (0.07) and soils (0.05).

Field investigation of roadside vegetative and structural barrier impact on near-road ultrafine particle concentrations under a variety of wind conditions

Roadside barriers, such as tree stands or noise barriers, are prevalent in many populated areas and have been shown to affect the dispersion of traffic emissions. If roadside noise barriers or tree stands are found to consistently lower ground-level air pollution concentrations in the near-road environment, this may be a practical strategy for reducing exposures to air contaminants along populated traffic corridors. This study measured ultrafine particle (UFP) concentrations using an instrumented mobile measurement approach, collecting data on major roadways and in near-road locations for more than forty sampling sessions at three locations in central North Carolina, USA. Two of the sampling sites had relatively thin tree stands, one evergreen and one deciduous, along a portion of the roadway. The third sampling site had a brick noise wall along a portion of the road. At 10m from the road, UFPs measured using a mobile sampling platform were lower by approximately 50% behind the brick noise wall relative to a nearby location without a barrier for multiple meteorological conditions. The UFP trends at the vegetative barrier sites were variable and the barrier effect is uncertain. In some cases, higher concentrations were observed behind the vegetative barrier, with respect to the clearing, which may be due to gaps in the thin tree stands allowing the transport of traffic-related air pollution to near-road areas behind the vegetation. On-road sampling revealed no consistent difference in UFP levels in on-road portions of the road with or without a roadside barrier present. These findings support the notion that solid roadside barriers may mitigate near-road impact. Given the co-benefits of vegetative barriers in the urban landscape, research regarding the mitigation potential of vegetative barriers of other configurations (e.g., greater density, wider buffer) is encouraged.

Radionuclides in the ground-level atmosphere in Vilnius, Lithuania, in March 2011, detected by gamma-ray spectrometry

This study presents the ground-level air monitoring results obtained in Vilnius, the capital of Lithuania, on 14 March–14 April 2011 after the recent earthquake and subsequent Tsunami having a crucial impact on Japanese nuclear reactors at the Fukushima Daiichi Nuclear Power Plant (NPP) on 11 March 2011. To collect representative diurnal aerosol samples a powerful sampling system ensuring the air filtration rate of 5500 m3 h−1 was used. The following artificial gamma-ray emitting radionuclides have been determined: 129mTe, 132Te (in equilibrium with its daughter 132I), 131I, 134Cs, 136Cs and 137Cs. Activity concentration of the globally distributed fission product 137Cs has increased from a background value of 1.6 μBq m−3 to the value of 0.9 mBq m−3 at the beginning of April. The activity ratio 134Cs/137Cs was found to be close to 1, with a slightly higher activity of 134Cs. The maximum aerosol-associated 131I activity concentration of 3.45 mBq m−3 was by four orders of magnitude lower than that measured at the same location in April–May 1986 as a consequence of the Chernobyl NPP accident. The estimated gaseous fraction of iodine-131 constituted about 70% of the total 131I activity.

Variations of210Pb concentrations in surface air at Thessaloniki, Greece (40°N)

Atmospheric concentrations of 210 Pb were measured over the year 2009 in ground level air at Thessaloniki, Northern Greece (40 ◦ 62 � N, 22 ◦ 95 � E). The mean activity concentrations of 210 Pb in surface air have been found to be 671 ± 213 μBq m −3 . The highest values of monthly atmospheric concentrations of 210 Pb were observed in the autumn and the lowest in the spring period. The higher values of 210 Pb during autumn were attributed to frequent inversion conditions of the surface layers, resulting in an enrichment of radon and its decay products in surface air. The lower values during the winter months might be due to the low emanation of radon from the frozen or snow-covered soil. The minima of 210 Pb concentrations during spring might reflect on higher washout during this period, which results in less emanation of radon from saturated with water soil, resulting in less production of 210 Pb near ground-level air. The relative high values during summer are probably due to the higher 222 Rn exhalation from the ground and due to the higher air mixing within the troposphere, which has as a result to carry down to the surface layer 210 Pb whose origin is older air masses which entered into the free troposphere. ∗ E-mail: anta@physics.auth.gr

Studies on the rain scavenging process of tritium in a tropical site in India

This study presents the results of one of the first systematic experiments on tritium ( 3H) concentrations in ground level air against that in rainwater near a pressurized heavy water reactor in a tropical region. The samples were collected over the rainy season of three years (2007, 2008 and 2010). For this study, 31 data sets were collected and interpreted based on the theoretical information available in the literature. The specific activity ratio of 3H between rainwater and air moisture at ground level was calculated for each data set. The average specific activity ratio was found to be 1.96 ± 2.72. A correlation ( r = 0.82, p < 0.001) was observed between the total rain hours in a day and the rainwater 3H activity. Higher rain duration with slower rain rate yielded higher 3H concentrations as more time was available for the scavenging/wash out process to take effect together with lower dilution. The present data also suggested the need to further investigate the influence of raindrop distribution and other local meteorological parameters on the 3H wash out process. An attempt was also made to predict the 3H concentration in air moisture samples using a Gaussian plume dispersion model and the values were compared with the measured 3H activity. The measured values were generally lower than the predictions.

Determination of Symmetrical Index for 3H in Precipitation and 137Cs in Ground Level Air

The paper presents results of a long-term investigations of tritium activity concentrations in precipitation and radiocesium activity concentrations in ground level air in Belgrade, Serbia. Samples were collected at three locations in Belgrade (Meteorological Station of Belgrade MS at Zeleno Brdo (ZB), Meteorological Station MS Usek (USEK), and Vinca Institute of Nuclear Sciences (VINS)). Presented data cover the period 1985–1997. Significantly higher tritium levels were measured in samples in VINS compared with off-site location, while the impact of research reactor for 137Cs was not detected. It was found that the value of the symmetrical index n is higher for VINS in case of tritium, compared to other locations, which is in accordance with the fact that the highest average monthly concentrations of tritium were obtained in the samples from the cited place. Although the highest value of index n in case of 137Cs was also obtained for VINS, average monthly concentrations of 137Cs in ground level air for this location were the lowest. The 137Cs concentration in the ground level air is described by a kinetic equation of the first order and provides a good description of the time changes in these concentrations.

7Be in ground level air in Daejeon, Korea

(7)Be concentrations in the ground level air in Daejeon, Korea were determined during the period of January 1998 to December 2009 by gamma-ray spectrometric analysis of particulate samples collected on filter paper with a high-volume air sampler. The monthly concentrations of (7)Be in the ground level air were in the range of 1.3-7.7 mBq m(-3) with strong seasonal trends of low values in the summer and high values in the spring and autumn. The annual mean values of (7)Be concentrations showed weak reverse correlation with the annual average sunspot number.

Growth, leaf traits and litter decomposition of roadside hybrid aspen ( Populus tremula L. × P. tremuloides Michx.) clones

Road traffic contributes considerably to ground-level air pollution and is therefore likely to affect roadside ecosystems. Differences in growth and leaf traits among 13 hybrid aspen ( Populus tremula × P. tremuloides) clones were studied in relation to distance from a motorway. The trees sampled were growing 15 and 30 m from a motorway and at a background rural site in southern Finland. Litter decomposition was also measured at both the roadside and rural sites. Height and diameter growth rate and specific leaf area were lowest, and epicuticular wax amount highest in trees growing 15 m from the motorway. Although no significant distance × clone interactions were detected, clone-based analyses indicated differences in genotypic responses to motorway proximity. Leaf N concentration did not differ with distance from the motorway for any of the clones. Leaf litter decomposition was only temporarily retarded in the roadside environment, suggesting minor effects on nutrient cycling.

Polonium-210 and lead-210 in the terrestrial environment: a historical review

The radionuclides 210Po and 210Pb widely present in the terrestrial environment are the final long-lived radionuclides in the decay of 238U in the earth’s crust. Their presence in the atmosphere is due to the decay of 222Rn diffusing from the ground. The range of activity concentrations in ground level air for 210Po is 0.03–0.3 Bq m −3 and for 210Pb 0.2–1.5 Bq m −3. In drinking water from private wells the activity concentration of 210Po is in the order of 7–48 mBq l −1 and for 210Pb around 11–40 mBq l −1. From water works, however, the activity concentration for both 210Po and 210Pb is only in the order of 3 mBq l −1. Mosses, lichens and peat have a high efficiency in capturing 210Po and 210Pb from atmospheric fallout and exhibit an inventory of both 210Po and 210Pb in the order of 0.5–5 kBq m −2 in mosses and in lichens around 0.6 kBq m −2. The activity concentrations in lichens lies around 250 Bq kg −1, dry mass. Reindeer and caribou graze lichen which results in an activity concentration of 210Po and 210Pb of about 1–15 Bq kg −1 in meat from these animals. The food chain lichen-reindeer or caribou, and Man constitutes a unique model for studying the uptake and retention of 210Po and 210Pb in humans. The effective annual dose due to 210Po and 210Pb in people with high consumption of reindeer/caribou meat is estimated to be around 260 and 132 μSv a −1 respectively. In soils, 210Po is adsorbed to clay and organic colloids and the activity concentration varies with soil type and also correlates with the amount of atmospheric precipitation. The average activity concentration levels of 210Po in various soils are in the range of 20–240 Bq kg −1. Plants become contaminated with radioactive nuclides both by absorption from the soil (supported Po) and by deposition of radioactive fallout on the plants directly (unsupported Po). In fresh leafy plants the level of 210Po is particularly high as the result of the direct deposition of 222Rn daughters from atmospheric deposition. Tobacco is a terrestrial product with high activity concentrations of 210Po and 210Pb. The overall average activity concentration of 210Po is 13 ± 2 Bq kg −1. It is rather constant over time and by geographical origin. The average median daily dietary intakes of 210Po and 210Pb for the adult world population was estimated to 160 mBq day −1 and 110 mBq day −1, corresponding to annual effective doses of 70 μSv a −1 and 28 μSv a −1, respectively. The dietary intakes of 210Po and 210Pb from vegetarian food was estimated to only 70 mBq day −1 and 40 mBq day −1 corresponding to annual effective doses of 30.6 μSv a −1 and 10 μSv a −1, respectively. Since the activity concentration of 210Po and 210Pb in seafood is significantly higher than in vegetarian food the effective dose to populations consuming a lot of seafood might be 5–15 fold higher.

HTO transport and OBT formation after nighttime wet deposition of atmospheric HTO onto land surface

To quantitatively evaluate OBT production after a nighttime wet deposition of atmospheric HTO onto land surface, numerical experiments using a sophisticated tritium transport model (SOLVEG-II) were conducted. For a nighttime rain actually observed at a grassland site, two hypothetical scenarios for wet deposition of HTO were made; 0.1-folded and 10-folded case, each having rain HTO concentration at 0.1 folds and 10 folds of equilibrium concentration of ground-level air HTO concentration. Calculation results showed atmospheric HTO concentration after the rain at 10-folded case was more than an order of magnitude larger than that at 0.1-folded case, affected by interception and evaporation of rain HTO with leaves, and, by a larger HTO re-emission from soil. After the rain, due to these heightened atmospheric HTO, TFWT concentration in leaf cellular water at 10-folded case kept an order, or more, larger than that at 0.1-folded case. As a result, OBT produced in leaves over nine-day after the rain at 10-folded case was 18 times larger than that at 0.1-folded case. We therefore concluded that nighttime wet deposition of HTO pronouncedly increases OBT formation if rain HTO concentration exceeds equilibrium concentration for the air HTO near the ground.

Joint multifractal description of the relationship between wind patterns and land surface air temperature

Land surface air temperature (SAT), registered at 1.25–2m above the ground, is influenced by wind patterns. As a consequence, some phenomena such as urban heat islands and the formation of ground-level air pollutants are affected. Detailed understanding of the effects of wind circulations on SAT is convenient to improve the knowledge of these phenomena. Thus, the joint multifractal analysis has been applied to describe time series recorded at Cordoba (southern Spain) from 2001 to 2008 revealing the presence of seasonal patterns related with warm and cold winds blowing from the SW (later spring and summer) and NE (later autumn and winter), respectively, that provoke different heterogeneity in SAT values. In addition, the extreme high SAT values seem to be related with summer SW winds. However, the presence of rare low SAT values produced by NE winds is less relevant.

Air ventilation in cities with dense high-rise developments

Ground-level air condition in inner city areas is becoming increasingly poor as buildings become taller and more closely spaced. This paper explains how wind flow in cities is primarily governed by the amount of air blowing in from outside and how this is modified by buildings, particularly taller ones. Based on experiences in Hong Kong, the paper shows how local topography affects the available wind and how city layouts, the configuration of building complexes and the geometry of individual buildings affect pedestrian-level wind speeds. Mitigation measures to improve air ventilation are proposed.

Radioactivity monitoring in ground level air in Belgrade urban area

Concentrations of beryllium-7 ((7)Be), lead-210 ((210)Pb) and caesium-137 ((137)Cs) were measured at two sites in the city of Belgrade (Serbia). One monitoring site was located in the central city area with heavy traffic and the other within the Institute of Nuclear Sciences Vinca, in the suburbs. Presented data cover the period 2004-9. Activity of the radionuclides was determined on an HPGe detector (Canberra, relative efficiency 23 %) by standard gamma spectrometry. Activities of (7)Be and (210)Pb exhibit a similar seasonal pattern. The mean monthly concentrations of (7)Be did not exceed 7 mBq m(-3). The maxima are correlated with the seasonal increase in temperature, whereas the minima are linearly correlated with the amount of precipitation. The activity of (210)Pb was below 0.9 mBq m(-3). The activities of both radionuclides were very low in winters and were largely affected by precipitation and snow coverage. Concentrations of (137)Cs were mainly below the limit of detection.

Difference in the air temperatures between the years of solar activity maximum and minimum and its mechanism

Based on large set of observational data (for ∼100 years), it has been demonstrated that the air temperature at midlatitudes in the years close to solar activity maximum is on average higher than in other years by DT = 0.11–0.15 degrees at many meteorological stations. The DT parameter is negative and smaller in magnitude near the equator and poles. A correct (in the energetic sense) physical mechanism by which solar and geomagnetic activities affect the ground level air temperature has been proposed.

대구 도심에 위치한 대규모 녹지공간의 냉섬 강도: 계절변화와 기상조건에의 관련성

Cool island intensity urban green space was investigated based in Dalsung Park, that is one of the largest parks in Daegu. Cool island intensity(CII), which is defined as the temperature difference between the green space and its surrounding built-up areas, shows time variations. A through-year measurement(2008-2009) of ground level air temperature revealed seasonal variation and relationship to the atmospheric condition of CII. The temperature variation in the park and the reference downtown Daegu was as same order as CII. The noontime CII is larger in summer than that in winter due to the leaf fall of the park trees. On the other hand, seasonal variation of nighttime CII is not so clear. The nighttime CII was larger under the stable atmosphere.

Environmental Radioxenon Levels in Europe: a Comprehensive Overview

Activity concentration data from ambient radioxenon measurements in ground level air, which were carried out in Europe in the framework of the International Noble Gas Experiment (INGE) in support of the development and build-up of a radioxenon monitoring network for the Comprehensive Nuclear-Test-Ban Treaty verification regime are presented and discussed. Six measurement stations provided data from 5 years of measurements performed between 2003 and 2008: Longyearbyen (Spitsbergen, Norway), Stockholm (Sweden), Dubna (Russian Federation), Schauinsland Mountain (Germany), Bruyeres-le-Châtel and Marseille (both France). The noble gas systems used within the INGE are designed to continuously measure low concentrations of the four radioxenon isotopes which are most relevant for detection of nuclear explosions: 131mXe, 133mXe, 133Xe and 135Xe with a time resolution less than or equal to 24 h and a minimum detectable concentration of 133Xe less than 1 mBq/m3. This European cluster of six stations is particularly interesting because it is highly influenced by a high density of nuclear power reactors and some radiopharmaceutical production facilities. The activity concentrations at the European INGE stations are studied to characterise the influence of civilian releases, to be able to distinguish them from possible nuclear explosions. It was found that the mean activity concentration of the most frequently detected isotope, 133Xe, was 5–20 mBq/m3 within Central Europe where most nuclear installations are situated (Bruyeres-le-Châtel and Schauinsland), 1.4–2.4 mBq/m3 just outside that region (Stockholm, Dubna and Marseille) and 0.2 mBq/m3 in the remote polar station of Spitsbergen. No seasonal trends could be observed from the data. Two interesting events have been examined and their source regions have been identified using atmospheric backtracking methods that deploy Lagrangian particle dispersion modelling and inversion techniques. The results are consistent with known releases of a radiopharmaceutical facility.

Short term variations of 7Be, 10Be concentrations in atmospheric boundary layer

To compare meteorological conditions, short term variations of atmospheric concentrations of 7 Be ( T 1/2 = 53.3 days) and 10 Be ( T 1/2 = 1.5 × 10 6 years) were investigated at Tokyo and Fukuoka, Japan, and Pacific Ocean nearby Japan. Atmospheric concentrations of 7 Be and 10 Be at anticyclone condition were higher than that at cyclone condition to a factor of 2–10. Because of being influenced by re-suspended components from soil ( 10 Be/ 7 Be > 1000), temporal variability of 10 Be/ 7 Be was high in daytime and low in nighttime. But when corrected for re-suspended component using Al concentration as an indicator of soil the 10 Be/ 7 Be ratio was constant. Comparing 7 Be and 10 Be concentrations with 212 Pb concentration as soil-generated component, we make a conclusion that high 7 Be and 10 Be concentration air mass is brought into boundary layer by high convection at daytime. Those diurnal variations were not observed in marine boundary layer. When cyclone passed through Fukuoka to Tokyo, which is 12 h behind, 7 Be and 10 Be concentrations also decreased with 12 h lag between Fukuoka and Tokyo. The 10 Be/ 7 Be ratio was constant during anticyclone to cyclone condition, and between Tokyo and Fukuoka. We conclude that after stratospheric aerosols enter into the upper troposphere they reside there for a certain period and mix uniformly in horizontal strata; later they are transported down to lower troposphere by anticyclone and penetrate into ground level air at daytime by convective strong mixing of boundary layer.

Ground-level Ozone Air Pollution in Vilnius City

The aim of the present study was to assess distribution of ground-level ozone concentration in Vilnius city. We used a portable Aeroqual series 300 ozone monitor. Sampling was carried out in Vilnius city during four seasons, during 2006-2007 years period. The results of this study revealed, that annual mean of ground-level ozone concentration in Vilnius city was 30,3 µgm -3 . The highest ground-level ozone concentration was in the Virsuliskiai district (43,1 µgm -3 ), lowest - at the highway of Eisiskės (17,9 µgm -3 ). The highest average seasonal concentration was determined during summer (49,6 µgm -3 ) and the lowest - during autumn (16,9 µgm -3 ). Ground-level ozone concentration also has a clear diurnal cycle, with higher values in day-time and notably lower values at night. Minimal ground-level ozone concentration was at 6 hour in morning (4,0 µgm -3 ), maximum at 13 hour (87,0 µgm -3 ). Concentration of ground-level ozone in Vilnius during measurement period had not exceeded the stated value (120,0 µgm -3 ). It is known that meteorological conditions influence formation and dispersion of ground-level ozone. Our results showed that ground-level ozone concentration correlated significantly with temperature (r= 0,554 p= 0,000) and wind speed (r= -0,785 p= 0,000).