Ground-level Air Research Articles

Trajectory Analysis of 210Pb and 7Be in Ground-Level Air in Southern Finland

The Finnish Meteorological Institute has been monitoring airborne natural radionuclides 210Pb and 7Be at its geophysical observatory at Nurmijuarvi, southern Finland (60°30'N, 24°39'E, h = 105 m above see level). Daily aerosol samples (3500 m3/d) were collected onto glass-fiber filters with an aerosol sampler having an aerodynamic cutoff diameter of 10-15 μm depending on the wind speed. The filters were analysed for 7Be with an electrically cooled HPGe γ-ray spectrometer and for 210Pb with α-counting of the daughter 210Po using an automatic α/β-analyzer. A trajectory analysis of the observed activity concentrations revealed that the highest 7Be and 210Pb activity concentrations are associated with continental air masses coming from southeast. Meteorologically these situations often originate from high-pressure areas in central Russia. The associated air masses are often dry, which prevents the removal of radionuclides through precipitation scavenging. 222Rn, and thus 210Pb too, originate practically entirely from land areas and not from oceans. The descending movement of air in high-pressure areas promotes the transfer of 7Be from upper air to the ground level. The production of 7Be increases toward the magnetic poles of the Earth. This is not reflected in the source areas of 7Be, because the concentration variations in the ground-level air are due to large-scale weather phenomena.

Investigation of Lublin town environment contamination by radionuclides and heavy metals with application of Parmeliaceae lichens

Contamination of ground level air at Lublin town was studied by measurements of radioactive isotope and heavy metal contents in Parmeliaceae lichens exposed during six months on the area of the town. The concentration of the elements studied was compared with these ones measured in unexposed (blank) samples of lichens. The highest increase of radioactivity was noticed for 232Th, 226Ra and 40K. The contamination by 137Cs does not increased markedly, ranging from 2 to 107 Bq/kg of the dry lichen sample. Nearly half of the exposed samples do not reveal any increase of cesium radioactivity. Heavy metal concentrations in analyzed lichens were low. From the results obtained, one may conclude that concentration of these metals in ground air level does not reach appreciable values.

Studies on radioactivity in aerosols as a function of meteorological variables in Salamanca (Spain)

Ambient concentrations of aerosol radioactivity in ground-level air were measured weekly in a low-industrialized city (Salamanca, Spain). Means of about 6.9×10 −5 and 4.83×10 −4 Bq m −3 were found for gross α and β activities, respectively, averaged over three years. The measured activities, which include contributions from several radionuclides in the ground atmosphere, were evaluated to determine the relationship between the meteorology and the aerosol activities in air. We have studied the influence of diverse meteorological parameters such as temperature, pressure and wind direction, as well as the effect of the less often considered terrestrial electrostatic field. Concentrations of gross α and β activities were greatly affected by the meteorological conditions, showing pronounced differences between seasons. The study reveals that much of the variability (approximately 50%) in the activities is explained by the electrostatic field, its influence being higher in winter. About 40% of the α and β variability is explained by both the temperature and the humidity. The influence of the wind direction is only statistically significant for α radioactivity. A simple mathematical model based on these variables is developed to describe globally the dynamics in air of radioactive particles enabling us to estimate the air radioactive background level.

Simulation of thermal and moisture-content conditions on the upper layer of peat soils

The problem of two-dimensional interrelated heat- and moisture-transfer in the upper layer of soil is formulated taking into account exchange by heat and moisture with the ground-level air layer. On its basis a difference scheme was constructed and algorithms and a program were developed to calculate the processes of heat and moisture transfer. We evaluated the effect of various meteorological and hydrological factors and the composition of organogenic rocks on the change in the temperature and moisture-content conditions of peat deposits and soils.

Spatial and temporal variability of ground-level ozone in Castilla-León (Spain).

Ozone is a secondary air pollutant that has received extensive attention in the literature, mainly because of the adverse effects that exposure to it can cause, particularly in vegetation during the growing season. Because meteorological conditions strongly influence the efficiency of photochemical processes leading to ozone formation and destruction, ground-level ozone air pollution is currently being considered as a regional-scale phenomenon rather than a local one. This role of O3 as a regional-scale pollutant often implies the handling of large data sets in order to obtain information about its spatial and temporal variability patterns over a given broad region. Rotated principal component analysis (RPCA) is known to be one of the most powerful mathematical tools that can be used to achieve this aim. RPCA was applied in this paper to the summer and winter hourly time series of ground-level O3, concentrations recorded during 2 consecutive years (1996-1997) at 26 urban and suburban sites in Castilla-León (Spain). This procedure permitted the identification of different subregions where O3 concentrations show different spatio-temporal variability patterns. These variability patterns are mainly associated with the interaction of regional-level meteorological and anthropogenic factors. Some differences between winter and summer patterns were also found.

A radioiodine speciation, deposition, and dispersion model with uncertainty propagation for the Oak Ridge dose reconstruction.

Between 1944 and 1956, radioactive 131I was released into the atmosphere from operations at the Oak Ridge National Laboratory in Oak Ridge, TN. The releases occurred from stacks and from building vents and openings in three different chemical forms: elemental, organic, and particulate. During their transport in the atmosphere, different forms of iodine react differently with other atmospheric chemicals and moisture, and are removed from the plume at different rates by the processes of dry and wet deposition. A modified Gaussian plume model was developed to address the processes of radioiodine speciation, deposition, depletion, and dispersion in the atmosphere, and to propagate uncertainties in input parameter values through to the ground-level concentrations of 131I in air. A unique approach was used to develop an implicitly correlated set of hourly meteorological parameters for any day of a month for each month of the year from ten years of available data between 1987 and 1996. The model was validated for both annual average and short-term releases. For the annual average releases, the predictions of ground-level concentrations of 131I from the model were within a factor of 2 of measured field data. For two of the three sets of available weekly data, the measurements fell within the 95% subjective confidence interval of model predictions. Predictions of ground-level air concentrations were made on an annual average basis for the entire period of release and on a short-term, episodic basis for a 1954 accident.

Monitoring of low-level radioactivity in ground-level air: γ-spectrometric measurements within IMIS / Spurenmessung radioaktiver Stoffe in der bodennahen Luft: γ-spektrometrische Messungen im Rahmen des „Integrierten Mess- und Informationssystems”

At the Braunschweig site of Physikalisch-Technische Bundesanstalt (PTB), a trace survey station for monitoring the radioactivity contained in ground-level air is operated within the framework of the German Integrated Measuring and Information System (IMIS) for monitoring environmental radioactivity and radioactivity contained in foodstuffs. In the routine operating mode of IMIS, the lower limits of detection (LLD) achieved for γ-ray emitting radionuclide measurements performed on aerosol ashes lie in the range from 0.1 μBq/m 3 to 0.02 μBq/m 3 . A software code for data management and time series evaluation is presented. Some examples of observed contaminations of the ground-level air with traces of artificial radionuclides are compiled.

Formula omitted] in ground-level air in Belgrade city area

Concentrations of 210 Pb in ground level air in the city area (Belgrade, Central Serbia) were measured in the period from 1985 to 1996. The activity of 210 Pb in air filters was determined on a HPGe detector by standard gamma spectrometry. Total standard error of the method was estimated to be below 25%. The average monthly concentrations of 210 Pb in the ground level air in the period from 1985 to 1996 were in the range of 0.30–3.17 mBq m −3 with the maxima in fall–winter periods and minimums in springs and early summers. The seasonal indices were 1.12–1.59 for fall–winter and 0.77–0.92 for spring–summer periods. The ratios of maximum-to-minimum concentrations in each year were relatively stable over the period, with slight increase in 1985, 1989 and 1995. The investigations are part of the long-term measurements of natural and man-made radionuclides in the ground-level air in the region.

Plutonium Isotopes in Ground-Level Air in Northern Germany Since 1990

The activity concentrations, ratios and seasonal fluctuations of plutonium isotopes in ground-level air in Northern Germany are reported for the years 1990 to 1997. The 239+240Pu activity concentrations (a) measured on quarterly samples lie in a range 0.4 nBq/m3<a<4 nBq/m3. The 238Pu activity concentrations are lesser by up to a factor of 0.1 (0.1 nBq/m3<a<0.8 nBq/m3). The total activity concentration shows a typical seasonal fluctuation in the time period under review. In a few quarterly samples the activity ratio of a(238Pu)/a(239+240Pu) is significantly increased.

Localizing Gaseous Fugitive Emission Sources by Combining Real-Time Optical Remote Sensing and Wind Data

ABSTRACT This paper presents a new approach to localize point emissions from ground-level fugitive gaseous air pollution sources. We estimate the crosswind plume's ground-level peak location downwind from the source by combining smooth basis functions minimization (SBFM) with path-integrated optical remote sensing concentration data acquired along the crosswind direction in alternating beam path lengths. Peak location estimates, in conjunction with real-time measured wind direction data, are used to reconstruct the fugitive source location. We conducted a synthetic data study to evaluate the proposed peak location SBFM reconstruction. Furthermore, the methodology was validated with open-path Fourier transform infrared concentration data collected with wind direction data downwind from a controlled point source. This approach was found to provide reasonable estimates of point source location. The field study reconstructed source location was within several meters of the real source location.

Temporal dynamics of airborne lead-210 in Missouri (USA): implications for geochronological methods

Lead-210 (210Pb) deposited from the atmosphere is used in the dating of certain geological materials such as glacial ice and lacustrine sediments, but its long-term atmospheric behavior has been little studied. The present investigation reports measurements of airborne 210Pb at 21 monitoring stations in Springfield, Missouri, during 1975–1995. Seasonal and diurnal patterns of atmospheric concentrations are established, and the mean annual concentrations of 210Pb in ground level air during the 20-year period are examined. Although airborne 210Pb concentrations are found to vary diurnally and seasonally, mean annual concentrations in southwest Missouri have remained relatively constant during this time period. This finding is important for geochronological methods that assume a constant 210Pb flux from the atmosphere.

Influences of the city of Bucharest on weather and climate parameters

Estimates of the urban heat island are presented based upon ground level air temperature measurement in a few representative points in Bucharest (May–December 1994). The intensity of the effect is analysed versus synoptic mesoscale patterns. Other effects of the urban area on some atmospheric parameters, particularly on cloud systems and precipitation, are presented, too, using radar images.

Intercomparison of nocturnal mixing height estimate methods for urban air pollution modelling

One of the most important meteorological input parameters for three-dimensional photochemical air pollution models is the mixing height h, which has a strong influence on the shape and intensity of the vertical diffusivity K z and, as a consequence, on ground-level air concentrations of primary and secondary pollutants. A number of indirect algorithms for the estimate of h in nocturnal, stable conditions, when the mixing is dominated by mechanical turbulence, are reviewed and compared with mixing heights derived from wind (SODAR) and temperature (RASS) profiles measured in the Milan urban area during spring and summer 1996. Mixing heights derived from temperature soundings correlate positively with those derived from wind soundings only when a stable layer is superimposed to a quasi-adiabatic layer, while the correlation is very weak in the presence of a ground-based inversion. In general, indirect algorithms perform very poorly if compared with RASS-based estimates, and reasonably well if compared with SODAR-based estimates. Among the others, Benkley and Schulman (1979, Journal of Applied Meteorology 18, 772–780) method, which makes use of wind speed observed at 10 m height, and Nieuwstadt (1984, Boundary-Layer Meteorology 30, 31–55), which makes use of friction velocity and Monin–Obukhov length, give the best results.

Growth variation of white oak subjected to historic levels of fluctuating air pollution

Growth of white oak ( Quercus alba L.) trees was examined, using tree-ring analysis, at three sites near a small, remote coal-fired power plant in central Pennsylvania, USA. Forests immediately adjacent to the power plant have been subjected to power plant emissions since the power plant initiated operation in 1954. However, localized, ground-level fumigations have been gradually reduced over the years due to a series of construction projects resulting in increased stack heights. Comparisons of growth were made among the white oaks growing at the three close-in sites, as well to the growth of white oak at three control sites located 10–50 km from the power plant, during periods of differing stack heights. White oak exhibited reduced growth at two of the close-in sites during the time period when historical ground-level air pollution exposures were assumed to be greatest due to low stack heights. White oak growth at the third close-in site was not substantially reduced during this time period. In 1976, taller stacks were implemented at the power plant to reduce local, ground-level concentrations of air pollutants. The recovery of tree growth at the two close-in affected sites, and increased synchronous growth responses from 1976–85 among all three close-in sites, indicates that implementation of taller stacks in 1976 reduced ground-level pollutant levels to such dosages that growth was not impaired at any site. Also, growth rates after 1976 were comparable to the growth rates of the white oaks growing on the control sites. A possible interacting factor was a severe drought that occurred in the mid-1960s in central Pennsylvania.

Abundance of airborne heterotrophic protists in ground level air of South Dakota

The abundance of heterotrophic protists (as protozoan cysts) in the near-surface tropospheric air of Rapid City, SD, was determined using a filtration sampler capable of collecting particles in the 2.0 to 20.0 μm size range (sampling rate ca. 16 l min −1). The number of viable cysts collected on the filter was estimated after enrichment cultivation in soil extract medium. Samples were mainly collected in the spring, fall and winter of 1997 and abundances throughout the year ranged from below detection (<0.05 m −3) to 1.08 cysts m −3 with an overall mean of 0.25 m −3 (SE=0.05). Not all of the isolates were identified to species but, over the study, 25 different morphotypes were found. Flagellates and naked amoebae were the commonest protozoa (as cysts) found; ciliates were rare. This reflects the abundance of these groups in soils, the likeliest source of most of the airborne protozoa in this study. The concentration of cysts generally increased as a function of the total particles in the atmosphere. The concentration of both particulates and cysts exhibited a wide range of variability, but highest values of both occurred on days with higher winds and lower relative humidity.

Concentration measurements of 7Be and 137Cs in ground level air in the Belgrade City area

Concentrations of 7Be and 137Cs in ground level air in the city area (Belgrade, central Serbia) were determined in the period from 1991–1996. The average monthly concentrations of 7Be in ground level air were in the range of 2–7 mBq/m 3 with pronounced one or two maxima in summer or early fall and a minimum in winter. The average air concentrations for 137Cs were from 0.5–8.5 × 10−5 Bq/m 3, with a spread maximum in the spring-summer period and a pronounced maximum during the winter. A general increase in 7Be and 137Cs concentrations during 1993 was recorded. The maximum seasonal indices were 1.3 for 7Be (summers) and 2.7 (late springs and early summers) and 3.4 (winters) for 137Cs. No correlation with the amount of precipitation and 137Cs concentrations in air was determined, while the washout effect of rainfalls seems to be more closely related with variations in 7Be concentrations.

Plutonium isotopes concentration in the ground level air and rain samples from Kraków

The aim of the present work was to look at the background levels of plutonium in air and rain samples. Two sets of Petryanov type filters through which ca. 0.5 Mm3 each of air had passed and two large samples of collected rain (170 L and 182 L) were analysed for the content of plutonium alpha-emitters. In the article the radiochemical procedure applied to these samples is described. Obtained Pu activities in air were 0.5±0.1 nBqm−3 and 0.7±0.1 nBqm−3 for238Pu and 3.1±0.2 nBqm−3 and 8.3±0.6 nBqm−3 for239+240Pu. Activities of rain samples were 7.5±0.7 mBqm−3 and 14.3±0.8 mBqm−3 for239±240Pu and 0.4±0.1 mBqm−3 and 2.1±0.2 mBqm−3 for238Pu, respectively, for the two samples. The most interesting finding is the largely different238Pu to239+240Pu activity ratios (from 0.03±0.01 to 0.18±0.01) measured in the samples. This result needs conformation, but as now it suggests different origins of plutonium isotopes in incoming to Krakow air.

A record of atmospheric 210Pb deposition in The Netherlands

The deposition flux of total atmospheric 210Pb has been measured at two sites in The Netherlands: Texel from 1992 to 1996 and Groningen from 1989 to 1994. With predominant westerly oceanic winds, the annual 210Pb deposition is relatively low as 222Rn, the source for atmospheric 210Pb, is mainly exhaled by the continents. The daily fluctuations in 210Pb deposition are determined by the almost random daily fluctuations in precipitation and the concentration in groundlevel air. The variations in annual 210Pb deposition flux appear to be mainly correlated with the number of heavy rains or thunder storms. This explains the variations in annual deposition at short distance. The average 210Pb deposition at Groningen (1987–1994) is 200 mBq m−2 day−1. The 210Pb deposition over the North Sea is estimated to be 115 mBq m−2 day−1 in the same period. The deposition velocity in Groningen is 1.0 cm s−1, which is similar to measurements in Virginia and Connecticut.

Infrared active gases are likely to change the dynamics and the stability of the atmosphere

Examination of the monthly ground-level air concentration of the spallation product Be 7 from up to three decades at 8 stations in 4 European countries shows a twofold trend for some specific months of the year. This trend is related to the month with the lowest concentration of the year and to the ratio of the month with the highest to that with the lowest concentration. Discussion of the possible causes for that trend leads to the conclusion that a steady change of the dynamic of the atmosphere can explain these findings. The positive trend of some seasonal Be 7 concentrations indicate a positive trend of the stratospheric/tropospheric exchange possibly connected with higher tropospheric vertical diffusion. The general finding is commensurate with the trend of exponentially growing concentration of climatic gases within the atmosphere during the last decades.

Temporal variation of 7Be and 210Pb size distributions in ambient aerosol

The size distributions of the cosmogenic 7Be and of the long-lived radon progeny 210Pb in ambient aerosols were measured continuously from December 1994 to the end of March 1996 in ground-level air at a semi-rural location in south Germany. Aerosol sampling was performed at a height of 4 m above ground with a low-pressure cascade impactor of the Berner type covering the size range from 0.06 to 16 μm and simultaneously with an high-volume sampler. Each sampling period was 10 d. Activities of 7Be and 210Pb were measured by gamma spectrometry and aerosol mass was determined gravimetrically. In all experiments the activity distributions of 7Be as well as of 210Pb were unimodal (log-normal) and associated with submicron aerosols of about 0.5–0.6 μm aerodynamic diameter. On average, the activity median diameters of 7Be (AMD: 0.57 μm) and of 210Pb (AMD: 0.53 μm) have been found to be significantly lower than the average mass median diameter (MMD: 0.675 μm) and higher or at most equal than the respective surface median diameter (SMD: 0.465 μm) of the aerosols: SMD⩽AMD Pb210<AMD Be7 <MMD. Variation of the atmospheric processes during the study period resulted in a variability of the activity median diameter between 0.44 to 0.74 μm for 7Be and from 0.28 to 0.74 μm for 210Pb. While in the winter months (October to April) a difference between the activity distributions of 210Pb (AMD: 0.595 μm) and 7Be (AMD: 0.59 μm) was not detectable, in summer, 210Pb was associated with significantly smaller aerosols (AMD: 0.43 μm) than 7Be (AMD: 0.52 μm). Comparing the activity median diameters observed in summer with those in winter, on average significantly lower diameters were found in summer pointing to shorter residence times in the summer months.