Sampling and physico-chemical analysis of precipitation: a review

Challenges in moving towards fog's contribution to spatial patterns of atmospheric deposition fluxes on a national scale

Fog is an important environmental phenomenon affecting, among other things, geochemical cycles via atmospheric deposition pathways. It is generally accepted that fog contributes substantially to atmospheric deposition fluxes especially in mountain forests. Nevertheless, due to intrinsic constraints, fog pathway has thus far been neglected in the quantification of atmospheric deposition and fog pathway has not been accounted for in nation-wide spatial patterns of atmospheric deposition of air pollutants. In this review we explore the causes as to why it is so complex to create a spatial pattern of fog contribution to atmospheric ion deposition fluxes on a national scale. Physical and chemical principles of fog formation are presented and factors influencing the abrupt temporal and spatial changes in both fog occurrence and fog chemistry are elucidated. The focus is on both constituents essential for fog deposition flux quantification, i.e. (i) hydrological input on fog water and (ii) chemistry of fog water.

Reconstruction of Daily Courses of SO42−, NO3−, NH4+ Concentrations in Precipitation from Cumulative Samples

It is important to study precipitation chemistry to comprehend both atmospheric and environmental processes. The aim of this study was the reconstruction of daily concentration patterns of major ions in precipitation from samples exposed for longer and differing time periods. We explored sulphates (SO42−), nitrates (NO3−) and ammonium (NH4+) ions measured in precipitation within a nation-wide atmospheric deposition monitoring network in the Czech Republic during 1980–2020. We visualised the long-term trends at selected individual years for four stations, Praha 4-Libuš (LIB), Svratouch (SVR), Rudolice v Horách (RUD) and Souš (SOU), differing in geographical location and reflecting different environments. We found anticipated time trends reflecting the emission patterns of the precursors, i.e., sharp decreases in SO42−, milder decreases in NO3− and steady states in NH4+ concentrations in precipitation. Statistically significant decreasing time trends in SO42− and NO3− concentrations in precipitation between 1990 and 2015 were revealed for the LIB and SVR sites. Spring maxima in April were found for all major ions at the LIB site and for NO3− for the SVR site, for both past and current samples, whereas no distinct seasonal behaviour was recorded for NH4+ at the RUD and SO42− at the SVR sites. By applying Bayesian modelling and the Integrated Nested Laplace Approximation approach, we were able to reconstruct the daily patterns of SO42−, NO3− and NH4+ concentrations in precipitation, which might be further utilised for a wide range of tasks, including comparison of magnitudes and shapes between stations, grouping the decomposed daily data into the ecologically motivated time periods, as well as for logical checks of sampling and measurement reliability.

Winter arsenic pollution in 10 forest ecosystems in the mountainous border regions of the Czech Republic

Arsenic (As) concentrations and deposition fluxes were measured in snow and rime at 10 mountain-top sites near the borders between the Czech Republic and Austria, Germany, Poland, and Slovakia during three consecutive winter seasons (2009-2011). Our study was performed at a time following several decades of sharply decreasing regional atmospheric pollution and following the 2006 implementation of stricter air quality standards across Europe. Our objective was to compare vertical and horizontal depositions of soluble and insoluble As forms throughout the Czech Republic and define a recent Central European As pollution gradient. Arsenic soluble in weak nitric acid contributed 83 to 85% to the total As deposition, with the remaining 17-15% bound to stable particulate forms. The highest As deposition rates were recorded in the eastern Czech Republic near the borders with Poland and Slovakia. Complementary hydrochemical monitoring in four mountain-slope catchments situated near selected main study sites revealed a further decrease in open-area As deposition by the end of 2018 in the east of the country. In contrast, spruce canopy throughfall flux did not change significantly between 2009-2011 and 2016-2018. The site-specific relative roles of coal-burning-derived and ore-smelting-derived atmospheric As are discussed.

Chemical Sensing Employing Plant Electrical Signal Response-Classification of Stimuli Using Curve Fitting Coefficients as Features

In order to exploit plants as environmental biosensors, previous researches have been focused on the electrical signal response of the plants to different environmental stimuli. One of the important outcomes of those researches has been the extraction of meaningful features from the electrical signals and the use of such features for the classification of the stimuli which affected the plants. The classification results are dependent on the classifier algorithm used, features extracted and the quality of data. This paper presents an innovative way of extracting features from raw plant electrical signal response to classify the external stimuli which caused the plant to produce such a signal. A curve fitting approach in extracting features from the raw signal for classification of the applied stimuli has been adopted in this work, thereby evaluating whether the shape of the raw signal is dependent on the stimuli applied. Four types of curve fitting models—Polynomial, Gaussian, Fourier and Exponential, have been explored. The fitting accuracy (i.e., fitting of curve to the actual raw signal) depicted through R-squared values has allowed exploration of which curve fitting model performs best. The coefficients of the curve fit models were then used as features. Thereafter, using simple classification algorithms such as Linear Discriminant Analysis (LDA), Quadratic Discriminant Analysis (QDA) etc. within the curve fit coefficient space, we have verified that within the available data, above 90% classification accuracy can be achieved. The successful hypothesis taken in this work will allow further research in implementing plants as environmental biosensors.

Bulk deposition close to a Municipal Solid Waste incinerator: one source among many

In order to assess the contribution of a Municipal Solid Waste incinerator to the area's total contamination, metals and soluble ions have been determined in bulk deposition collected at sites affected by different levels of plant emissions, according to the results of the Calpuff air dispersion model. Results show that in general fluxes monitored at the different sites during the same period are quite similar for each analyte. Deposition fluxes of nitrite and ammonium are significantly lower at the more distant site, while copper is significantly higher at this site, possibly because of copper fungicide used on the nearby agriculture land. The presence of sea spray and resuspended soil dust can be inferred from Pearson correlation coefficients, while enrichment factors indicate that Cu, Pb and Zn have a probable anthropogenic origin. A more complete evaluation of the sources affecting the area was obtained with PMF analysis. The sources associated with each factor were identified from the source profile and temporal trends. Six factors were identified, three sources associate with natural matrices, while three factors represent anthropogenic sources. The greatest contribution of heavy metals, the most toxic and persistent components determined, is associated with resuspended soil dust, especially when weighted according to their toxicity. The anthropogenic source contribution is similar at all sites, and therefore the incinerator's relative contribution to the total pollutant load appears to be negligible compared to other sources affecting the area.

Investigation of mercury wet deposition physicochemistry in the Ohio River Valley through automated sequential sampling

Intra-storm variability and soluble fractionation was explored for summer-time rain events in Steubenville, Ohio to evaluate the physical processes controlling mercury (Hg) in wet deposition in this industrialized region. Comprehensive precipitation sample collection was conducted from July through September 2006 using three different methods to evaluate both soluble and insoluble fractions as well as scavenging and washout properties of Hg and a suite of trace elements. Real-time filtration of event total precipitation revealed that 61±17% (mean±standard deviation) of Hg in wet deposition was in a soluble form. Comparison of total and dissolved element concentrations (solubility fractionation) showed the following order of decreasing solubility: S>Na>Se>Ca>Mg>Hg>As>Mn>V>Cr>Fe>La≈Ce ranging from 95% (S) to 4% (Ce). To examine removal mechanisms occurring during the course of a precipitation event, discrete, sequential sub-event precipitation samples were collected. Results indicated that Hg had lower "scavenging coefficients" (the rate of Hg concentration decrease throughout the events) than the majority of elements analyzed, indicating that either (i) Hg is incorporated into rain via gas phase inclusion or particulate nucleation within cloud, or (ii) Hg is available in the boundary layer for scavenging, even in the latter stages of precipitation. The Hg scavenging coefficient (-0.39) was low compared to S (-0.73), a co-pollutant of Hg. When compared to an upwind, regionally representative site, the scavenging coefficient of Hg for the locally influenced precipitation was 25% lower. This observation suggests that a continuous feed of soluble Hg was the reason for the low scavenging coefficient. Overall, this investigation of Hg wet deposition in Steubenville indicates that the physical and chemical properties of Hg emissions are driving the elevated deposition rates observed near point sources.

Effect of acid rain on building material of the El Tajín archaeological zone in Veracruz, Mexico

Three limestone slabs (approx. 20 cm2 each) were extracted from the El Tajin archaeological zone in Veracruz, Mexico. X-ray diffraction analysis revealed three components: calcite (81.2%), quartz (17.9%) and feldspar (0.9%). Calcite content by x-ray diffraction analysis was slightly higher than that determined by chemical reaction between the limestone sample and nitric acid. The latter analysis, carried out in triplicate, yielded a calcite content of 77.1%. Mean water absorption, density and porosity of the limestone samples were also determined. Dissolution of limestone samples was investigated using an experimental rainfall simulation chamber, in which the stone samples were irrigated with artificial rain matching the pH and the ionic composition with 40 rainfall samples collected at El Tajin from August 18, 2002, to April 9, 2003. According to calcium and bicarbonate net concentrations found in the effluent of the chamber, a chemical mechanism by which limestone at El Tajin is dissolved by acid rain is proposed. A model used to investigate the air transport pathways corresponding to precipitation events at El Tajin shows that air parcels come mainly from the Gulf of Mexico, although no directional preference is evident for acidic vs. non-acidic events.

Sampling of atmospheric precipitation and deposits for analysis of atmospheric pollution

This paper reviews techniques and equipment for collecting precipitation samples from the atmosphere (fog and cloud water) and from atmospheric deposits (dew, hoarfrost, and rime) that are suitable for the evaluation of atmospheric pollution. It discusses the storage and preparation of samples for analysis and also presents bibliographic information on the concentration ranges of inorganic and organic compounds in the precipitation and atmospheric deposit samples.

Practical considerations for addressing uncertainties in monitoring bulk deposition

The assessment of the deposition of both wet (rain and cloud) and dry sedimenting particles is a prerequisite for estimating element fluxes in ecosystem research. Many nations and institutions operate deposition networks using different types of sampler. However, these samplers have rarely been characterized with respect to their sink properties. Major errors in assessing bulk deposition can result from poor sampling properties and defective sampling strategies. Relevant properties are: sampler geometry and material, in particular the shape of the rim; sink properties for gases and aerosols; and microbial transformations of the collected samples. An adequate number of replicates allows the identification of samples which are contaminated, in particular by bird droppings. The paper discusses physical and chemical properties of the samplers themselves. The dependence of measurement accuracy on the number of replicates and the sampling area exposed is discussed. Recommendations are given for sampling strategies, and for making corrections and substitution of missing data.

Environmental VOSCs--formation and degradation of dimethyl sulfide, methanethiol and related materials

Volatile organic sulfur compounds (VOSCs) play a major role in the global sulfur cycle. Two components, dimethyl sulfide (DMS) and methanethiol (MT) are formed in large amounts by living systems (e.g. algae, bacteria, plants), particularly in marine environments. A major route to DMS is by action of a lyase enzyme on dimethylsulfoniopropionate (DMSP). DMSP has other roles, for instance as an osmoprotectant and cryoprotectant. Demethiolation of DMSP and other materials leads to MT. A major transport process is release of DMS from the oceans to the atmosphere. Oxidation of DMS in the atmosphere by hydroxyl and nitrate radicals produces many degradation products including CO2, COS, dimethyl sulfoxide, dimethyl sulfone, organic oxyacids of sulfur, and sulfate. These materials also have roles in biotic processes and there are complex metabolic interrelationships between some of them. This review emphasizes the chemical reactions of the organic sulfur cycle. For biotic reactions, details of relevant enzymes are provided when possible.

Effects of atmospheric ammonia (NH3) on terrestrial vegetation: a review

At the global scale, among all N (nitrogen) species in the atmosphere and their deposition on to terrestrial vegetation and other receptors, NH3 (ammonia) is considered to be the foremost. The major sources for atmospheric NH3 are agricultural activities and animal feedlot operations, followed by biomass burning (including forest fires) and to a lesser extent fossil fuel combustion. Close to its sources, acute exposures to NH3 can result in visible foliar injury on vegetation. NH3 is deposited rapidly within the first 4-5 km from its source. However, NH3 is also converted in the atmosphere to fine particle NH4+ (ammonium) aerosols that are a regional scale problem. Much of our current knowledge of the effects of NH3 on higher plants is predominantly derived from studies conducted in Europe. Adverse effects on vegetation occur when the rate of foliar uptake of NH3 is greater than the rate and capacity for in vivo detoxification by the plants. Most to least sensitive plant species to NH3 are native vegetation > forests > agricultural crops. There are also a number of studies on N deposition and lichens, mosses and green algae. Direct cause and effect relationships in most of those cases (exceptions being those locations very close to point sources) are confounded by other environmental factors, particularly changes in the ambient SO2 (sulfur dioxide) concentrations. In addition to direct foliar injury, adverse effects of NH3 on higher plants include alterations in: growth and productivity, tissue content of nutrients and toxic elements, drought and frost tolerance, responses to insect pests and disease causing microorganisms (pathogens), development of beneficial root symbiotic or mycorrhizal associations and inter species competition or biodiversity. In all these cases, the joint effects of NH3 with other air pollutants such as all-pervasive O3 or increasing CO2 concentrations are poorly understood. While NH3 uptake in higher plants occurs through the shoots, NH4+ uptake occurs through the shoots, roots and through both pathways. However, NH4+ is immobile in the soil and is converted to NO3- (nitrate). In agricultural systems, additions of NO3- to the soil (initially as NH3 or NH4+) and the consequent increases in the emissions of N2O (nitrous oxide, a greenhouse gas) and leaching of NO3- into the ground and surface waters are of major environmental concern. At the ecosystem level NH3 deposition cannot be viewed alone, but in the context of total N deposition. There are a number of forest ecosystems in North America that have been subjected to N saturation and the consequent negative effects. There are also heathlands and other plant communities in Europe that have been subjected to N-induced alterations. Regulatory mitigative approaches to these problems include the use of N saturation data or the concept of critical loads. Current information suggests that a critical load of 5-10 kg ha(-1) year(-1) of total N deposition (both dry and wet deposition combined of all atmospheric N species) would protect the most vulnerable terrestrial ecosystems (heaths, bogs, cryptogams) and values of 10-20 kg ha(-1) year(-1) would protect forests, depending on soil conditions. However, to derive the best analysis, the critical load concept should be coupled to the results and consequences of N saturation.