Influence of peat fires on the rainwater chemistry in intra-mountain basins with specific atmospheric circulations (Eastern Carpathians, Romania)

Chemical evolution of rainfall in China's first eco-civilization demonstration city: Implication for the provenance identification of pollutants and rainwater acid neutralization

Rainfall chemistry is a vital indicator for reflecting anthropogenic/natural input on atmospheric quality, and the rainfall process is also the main sink of air contaminants, which has received widely concerns by all walks of life. However, the chemical compositions, sources of major solutes, historical evolution, and their determinants of rainwater in Chinese urban area, which is hotspot of atmospheric pollutant emission, are unclear under the dual background of fast economic development and eco-civilization construction. To decipher these issues, the latest year data of observation-based rainwater chemistry and the historical rainwater data, and air pollution data of China's first eco-civilization demonstration city were integrated and studied. The results presented that SO42- (53.4 %) and NO3- (28.8 %), Ca2+ (46.5 %) and NH4+ (37.9 %) dominated the present rainwater anions and cations. The historical changes in the relative proportion of rainwater ions (e.g., the holistic decreasing trend of SO42-) revealed the reduction and management achievement of atmospheric pollutant emission driven by different stages of eco-civilization city construction. The atmospheric components were well removed by rainfall scouring and all the rainwater ions showed obvious temporal variations. The concentrations of most of ions were higher in winter but lower in summer due to the key factors of meteorological factor (mainly rainfall amount) and the seasonal variations of source contribution. The stoichiometry-based source identification and relative contribution calculation reflected that anthropogenic input was the most primary contributor of NO3- (99.4 %) and SO42- (95.4 %), and the contribution of fixed emission source was relatively higher than that of traffic sources. The NH4+ was defined as the anthropogenic input ion (urban wastes and fuel combustion), while all Cl- and Na+ were from oceanic input. In contrast, terrigenous input represented the most important origin of Ca2+, K+, and Mg2+, with relative contribution of 99.5 %, 97.0 %, and 90.7 %, respectively. The high neutralization factor (NF, about 2.0) values and neutralizing to acidifying potential (NP/AP, about 1.7) ratios and their increasing trend in past few decades revealed the fact of rainwater acid being highly neutralized under the background of eco-civilization city construction.

Phylogeny and functional diversity of halophilic microbial communities from a thalasso environment

The El-Rawda solar saltern, located in North Sinai, Egypt, is formed through the process of water evaporation from the Bradawil lagoon. This evaporation leads to the precipitation of gypsum, halite minerals, and salt flats, which subsequently cover the southern and eastern areas of the lagoon. This study employed the shotgun metagenomic approach, the illumine platform, and bioinformatic tools to investigate the taxonomic composition and functional diversity of halophilic microbial communities in solar saltern. The metagenomic reads obtained from the brine sample exhibited a greater count compared to those from the sediment sample. Notably, the brine sample was primarily characterized by an abundance of archaea, while the sediment sample displayed a dominant abundance of bacteria. Both samples exhibited a relatively low abundance of eukaryotes, while viruses were only found in the brine sample. Furthermore, the comparative analysis of functional pathways showed many important processes related to central metabolism and protein processing in brine and sediment samples. In brief, this research makes a valuable contribution to the understanding of very halophilic ecosystems in Egypt, providing insights into their microbial biodiversity and functional processes.

Effects of Air Pollutants from Wildfires on Downwind Ecosystems: Observations, Knowledge Gaps, and Questions for Assessing Risk

Wildfires have increased in frequency and area burned, trends expected to continue with climate change. Among other effects, fires release pollutants into the atmosphere, representing a risk to human health and downwind terrestrial and aquatic ecosystems. While human health risks are well studied, the ecological impacts to downwind ecosystems are not, and this gap may present a constraint on developing an adequate assessment of the ecological risks associated with downwind wildfire exposure. Here, we first screened the scientific literature to assess general knowledge about pathways and end points of a conceptual model linking wildfire generated pollutants and other materials to downwind ecosystems. We found a substantial body of literature on the composition of wildfire derived pollution and materials in the atmosphere and subsequent transport, yet little observational or experimental work on their effects on downwind ecological end points. This dearth of information raises many questions related to adequately assessing the ecological risk of downwind exposure, especially given increasing wildfire trends. To guide future research, we pose eight questions within the well-established US EPA ecological risk assessment paradigm that if answered would greatly improve ecological risk assessment and, ultimately, management strategies needed to reduce potential wildfire impacts.

Understanding the origins of and influences on precipitation major ion chemistry on the Island of O'ahu, Hawai'i

Precipitation is the primary groundwater source for the Island of O'ahu, Hawai'i, USA, and is an important source of terrestrial nutrients. Since Pacific Islands are particularly vulnerable to the impacts of climate change, they are important venues for studying the controls on and fluctuations in precipitation chemistry. Spatial variations in some of the dissolved rainfall ions can also be of value as natural geochemical tracers in examining surface and groundwater flow. This study collected and chemically analyzed bulk precipitation from 20 sites across the Island of O'ahu approximately quarterly between April 2018 and August 2021. The new precipitation chemistry data were integrated with previously published precipitation data to characterize major ion composition and examine the atmospheric processes controlling inorganic ion deposition. Linear regression and multivariate analysis were used to quantify the relationships among major ions and to assess the impacts of various environmental and meteorological factors on precipitation chemistry. Ordinary kriging and inverse distance weighted interpolations were conducted to help visualize spatial variations in major ion deposition. The results clearly indicate that ocean sea spray is the primary driver of precipitation inorganic chemistry, with marine sea salt aerosols accounting for more than 90% of the measured ion load. However, they also show that various weather patterns and nutrient sources impact inorganic deposition. Most notably, upper atmospheric transport of Asian continental dust during Hawaiian wet seasons, Ca2+ from local sedimentary deposits, and anthropogenic K+ from agricultural activity appear to be substantial non-marine deposition sources. This study synthesizes data from multiple sources into the most spatially and topographically diverse precipitation collector network on O'ahu to date. The findings from this effort help establish a baseline for assessing future fluctuations in inorganic ion deposition and lay important groundwork for examining connections between precipitation and groundwater chemistry within the study area.

Investigation of the chemical nature of precipitation and source apportionment of its constituents in Tehran metropolis, Iran

Precipitation is a key process for purifying the atmosphere of pollutants. However, precipitation chemistry is also a significant environmental catastrophe on a global scale. Tehran Metropolitan Area, Iran's capital, is one of the world's most polluted cities. Nonetheless, little effort has been paid to determining the chemical composition of precipitation in this polluted metropolis. The chemical components and likely sources of trace metals and water-soluble ions in precipitation samples collected from 2021 to 2022 at an urban location in Tehran, Iran, were investigated in this study. The pH of the rainwater samples varied from 6.330 to 7.940 (mean 7.313, volume weighted mean (VWM) 7.523). The following is the order of the VWM concentration of main ions: Ca²⁺ > HCO₃^- > Na⁺ >SO₄^2- > NH₄⁺ > Cl^- > NO₃^- > Mg²⁺> K⁺> F^-. Furthermore, we discovered that VWM concentrations for trace elements are modest, with the exception of Sr (39.104 eq L^-1). The primary neutralizing species for precipitation acidity were Ca²⁺ and NH₄⁺. Vertical feature mask (VFM) diagrams derived from cloud-aerosol lidar and infrared pathfinder satellite observation (CALIPSO) track data indicated that polluted dust was the most common pollutant in the Tehran sky that might contribute significantly to the neutralization of precipitation. A study of species concentration ratios in seawater and the earth's crust indicated that virtually all Se, Sr, Zn, Mg²⁺, NO₃^-, and SO₄^2- were anthropogenic. While Cl^- was largely obtained from sea salt, K⁺ was obtained from both the earth's crust and the sea, with the earth's crust playing a larger role in K⁺. The earth's crust, aged sea salt, industry, and combustion processes were all verified as sources of trace metals and water-soluble ions by positive matrix factorization analysis.

Comparison of rainwater quality before and during the MCO using chemometric analyses

This study aimed to classify the spatiotemporal analysis of rainwater quality before and during the Movement Control Order (MCO) implementation due to the COVID-19 pandemic. Chemometric analysis was carried out on rainwater samples collected from 24-gauge stations throughout Malaysia to determine the samples' chemical content, pH, and conductivity. Other than that, hierarchical agglomerative cluster analysis (HACA) and discriminant analysis (DA) were used to classify the quality of rainwater at each location into four clusters, namely good, satisfactory, moderate, and bad clusters. Note that DA was carried out on the predefined clusters. The reduction in acidity levels occurred in 11 stations (46% of overall stations) after the MCO was implemented. Chemical content and ion abundance followed a downward trend, indicating that Cl^- and Na⁺ were the most dominant among the anions and cations. Apart from that, NH₄⁺, Ca²⁺, NO₃^-, and SO₄^2- concentrations were evident in areas with significant anthropogenic activity, as there was a difference in the total chemical content in rainwater when compared before and during the MCO. Based on the dataset before the MCO, 75% of gauge stations were in the good cluster, 8.3% in the satisfactory cluster, 12.5% in the moderate cluster, and 4.2% in the bad cluster. Meanwhile, the dataset during the MCO shows that 72.7% of gauge stations were in the good cluster, 9.1% in the satisfactory cluster, 9.1% in the moderate, and 4.5% in the bad cluster. From this study, the chemometric analysis of the year 2020 rainwater chemical composite dataset strongly indicates that reduction of human activities during MCO affected the quality of rainwater.

Chemometric approach to evaluate the chemical behavior of rainwater at high altitude in Shaune Garang catchment, Western Himalaya

The present research has been performed to analyze the chemical behavior of rainwater of the Shaune Garang catchment (32.19° N, 78.20° E) in the Baspa basin, located at a high elevation (4221 m above mean sea level) in the Himachal Himalaya, India. During the study period, sixteen rainwater samples were collected from the Shaune Garang catchment at five different sites. The volume-weighted mean (VWM) pH value of rainwater ranged between 4.59 and 6.73, with an average value of 5.47 ± 0.69, indicating the alkaline nature of rainfall. The total ionic strength in the rainwater ranged from 113.4 to 263.3 µeq/l with an average value of 169.1 ± 40.4 µeq/l. The major dominant cations were Ca²⁺ (43.10%) and Na⁺ (31.97%) and anions were Cl⁻ (37.68%), SO₄²⁻ (28.71%) and NO₃⁻ (23.85%) in rainwater. The ionic ratios were calculated among all the ions. The fraction of (NO₃⁻  +Cl⁻) with SO₄²⁻ was measured as 2.3, which specifies sour faces of rainwater due to HNO₃, H₂SO₄, and HCl. A multivariate statistical assessment of rainwater chemistry through Principal Component Analysis (PCA) shows the significance of four factors controlling 78.37% of the total variance, including four-component (PC1 explained 27.89%, PC2 explained 24.98%, PC3 explained 14.64%, PC4 explained 10.85%). However, the individual contribution of Factor 1(PC1) explains 27.89% of the total variance (78.37%) and displays a strong optimistic loading for Ca²⁺ and Cl⁻. Further, high loading of Ca²⁺ and NO₃⁻ and moderate loading of SO₄²⁻ signify the contribution of burning fossil fuel and soil dust. Anthropogenic and natural pollutants influence the composition of rainwater in the pristine Himalayas due to local and long-distance transportation. The study area receives precipitation from the West and North-West, transporting dust and fossil fuel emissions from the Thar Desert and Northwestern countries.

Chemical Composition Characteristics and Source Contributions of Precipitation in Typical Cities on the North Slope of Tianshan Mountain in Xinjiang during 2010–2019

This work presents the results of a ten-year investigation (2010–2019) on the characteristics and sources of precipitation pollution in typical cities locating in the economic belt on the North Slope of Tianshan Mountain, Xinjiang. The water-soluble ions’ characteristics (Na+, NH4+, K+, Mg2+, Ca2+, F−, Cl−, SO42−, NO3−), neutralizing capacity, wet deposition and sources of precipitation in Urumqi, Karamay and Yining during 2010–2019 were compared and analyzed. The study showed that from 2010 to 2019, the pH value of precipitation in Urumqi, Karamay and Yining varied from 4.18 to 10.55 with a volume-weighted mean (VWM) pH of 6.33, and the pH value showed an upward trend overall. The VWM electrical conductivity (EC) of the precipitation was the highest in Urumqi and the lowest in Yining, indicating that Urumqi was the most polluted and Yining was relatively clean. The most important cation in the precipitation of the three cities was Ca2+, and the most important anion was SO42−. The ratio of SO42−/NO3− indicated that the air pollution in Urumqi and Yining belonged to the typical coal-smoke air pollution, while there was compound pollution in Karamay. As can be seen from the neutralization factor, Ca2+ had the strongest neutralization ability, followed by Na+ and NH4+. Nitrate and sulfate in the atmosphere of Urumqi, Karamay and Yining are likely to exist in the form of NH4NO3, CaSO4 and (NH4)2SO4•CaSO4•2H2O. Wet deposition flux analysis of S and N showed that S pollution of the precipitation in Urumqi showed a decreasing trend, while N pollution showed an increasing trend. S pollution of the precipitation in Karamay gradually decreased, while N pollution of the precipitation in Yining became more and more serious. By analyzing origins of major ions in precipitation, it is concluded that human activities (industry, agriculture, heating, and transportation) are the main sources of ions in precipitation, and natural sources (soil dust) also play an important role.

Changes of precipitation acidity related to sulfur and nitrogen deposition in forests across three continents in north hemisphere over last two decades

Through synthesizing bulk precipitation chemistry in forest sites (n = 128) from three monitoring networks, (NADP in Northern America, EMEP in Europe, and EANET in East Asia), this study quantifies the temporal changes of precipitation acidity and its dominant acidifying agents over the last two decades. Results show distinct declines of sulfate and nitrate depositions and increases of precipitation pH in northeast America and central and east Europe, but not in Asia during 1999 and 2018. The decreases of sulfate and nitrate depositions likely reflect the long-term effort of pollutant emission controls. The temporal pattern of sulfate (SO₄^2-)/nitrate (NO₃^-) and ammonium nitrogen (NH₄-N)/nitrate nitrogen (NO₃-N) equivalent ratios indicate that acid rain in the NADP and EMEP have transitioned from sulfate-dominated to nitrate-dominated, and the DIN deposition has shifted from nitrate-dominated to ammonium-dominated in recent years, owing to reductions of sulfur dioxides (SO₂) and nitrogen oxides (NOx) emissions. In contrast, sulfate still plays a dominant role on the acidity of precipitation than nitrate in Asia, and NH₄-N deposition also has a significant contribution in N flux due to increasing trends of ammonia emissions in Southeast Asia.

Climate-induced Arctic-boreal peatland fire and carbon loss in the 21st century

Boreal peatlands are increasingly vulnerable to wildfires as climate change continues accelerating. Fires consume substantial quantities of organic soils and rapidly transfer large stocks of terrestrial carbon to the atmosphere. Herein, we quantify the minimum environmental temperature from -45 °C to 45 °C that allows the moist peat to smolder, as the fire threshold of peatlands. We then apply a typical vertical soil temperature profile to estimate the future depth of burn and carbon emissions from boreal peatland fires under the impact of global warming. If the boreal region continues warming at a rate of 0.44 °C/decade, we estimate the carbon loss from the boreal peat fires on a warmer soil layer may increase from 143 Mt. in 2015 to 544 Mt. in 2100 and reach a total of 28 Gt in the 21st century. If the global human efforts successfully reduce the boreal warming rate to 0.3 °C/decade, the peat fire carbon loss would drop by 21% to 22 Gt in the 21st century. This work helps understand the vulnerability of boreal peatland to more frequent and severer wildfires driven by global warming and estimate climate-induced carbon emissions from boreal peatland fires in the 21st century.

Rainwater chemistry observation in a karst city: variations, influence factors, sources and potential environmental effects

The rainwater chemistry and related air contaminants are used to investigate the rainwater ions sources, variations, and influence factors from 2012 to 2014 in Guiyang city (the typical karst urban area of Southwest China). According to temporal rainwater ion concentrations, the obvious variations were presented in the study period, such as Ca²⁺ (125∼6,652 μeq L⁻¹) and SO₄²⁻ (11∼4,127 μeq L⁻¹). Consequently, Ca²⁺, Mg²⁺, SO₄²⁻ and Cl⁻ are considered as the leading ions. Three critical influencing factors of rainwater ions concentrations, including sources variations, rainfall amount and long-distance migration (rainfall amount > 100 mm) are identified. Based on the typical ionic ratios, source identification suggested that anthropogenic inputs mainly contributed to F⁻, NO₃⁻ and SO₄²⁻, while the dusts (crustal sources) are the primary sources of Mg²⁺, Ca²⁺ and K⁺. Cl⁻ Enrichment in long-distance transport is the main contributor of Cl⁻. According to the observation of high level of total wet acid deposition, the more detailed spatio-temporal monitoring of rainfall-related acid deposition (particularly sulfur deposition) is required to understand its potential environmental effects in the aquatic ecosystem of the earth surface.

Human health impact assessment and temporal distribution of trace elements in Copșa Mică- Romania

The present study aims to analyze the temporal variations of PM₁₀ and to assess the health risk indexes caused by trace elements from particulate matter (PM₁₀) via inhalation, ingestion, and dermal absorption by adults and children in Copșa Mică (Romania) during 2009–2019. The results revealed a high multi-annual mean concentration of PM₁₀ and trace elements. The analyzed air pollutants showed a decreasing trend during the studied years, therefore 44.11%, 43.48%, 36.07%, 16.02%, and 15.80% lower values were observed for As, Cd, Ni, PM₁₀, and Pb, respectively, due to environmental regulations. The daily exceedance percentage of Pb and Cd was very high, representing 21.74% and 11.26%, followed by PM₁₀ and As concentrations with 4.72% and 3.92%. The ratio between the trace element concentration measured in Copșa Mică and the country average was 2.46, 4.01, 2.44 and 10.52 times higher for As, Cd, Ni and Pb. The calculated Hazard Quotient values via inhalation were higher than the safe limit (1), which accounted 1.81, 3.89 and 4.52, for As, Cd and Ni, respectively, indicating that the trace elements might present a non-carcinogenic risk to both adults and children. Furthermore, the concentration of all studied trace elements in Copșa Mică showed cancer risk for adults via inhalation and dermal absorption as well.

Spatial distribution of trace elements (As, Cd, Ni, Pb) from PM10 aerosols and human health impact assessment in an Eastern European country, Romania

In the present study, the concentrations of trace elements in PM₁₀ were determined and analyzed at 115 monitoring stations in Romania throughout the period 2009-2018. The spatiotemporal distribution of trace element concentrations of PM₁₀, the source apportionment and health impact assessment, was carried out. The results showed a very high multi-annual mean concentration for PM₁₀ and trace elements as well. The multiannual average concentration of PM₁₀ was higher by 29.75% than the World Health Organization recommendation. All studied air pollutants showed a decreasing trend during the studied years, showing with 17.84%, 50.21%, 43.36%, 11.27%, and 72.09% lower values for PM₁₀, As-, Cd-, Ni-, and Pb-, respectively, due to environmental regulations. To assess the human health impact, the hazard quotient (HQ) and cancer risk (CR) were calculated using the health risk model developed by the US Environmental Protection Agency (EPA). The Cd and Ni might present a non-carcinogenic risk to both adults and children; however, the hazard quotient values are higher than the safe limit, with 9.53 and 1.93, respectively. In addition, our study results revealed that the inhalation of As, Cd and the dermal absorption of all studied trace elements were considered as the most important risk factors for developing cancer, especially in case of adults.

Effects of PM10 and Weather on Respiratory and Cardiovascular Diseases in the Ciuc Basin (Romanian Carpathians)

This study presents the PM10 concentration, respiratory and cardiovascular disease hospital admissions evolution in the Ciuc basin for a period of 9 years (2008–2016), taking into consideration different meteorological conditions: boundary layer, lifting condensation level, temperature-humidity index, and wind chill equivalent chart index. The PM10 and hospital admissions evolution showed a very fluctuated hourly, weekly, monthly, yearly tendency. The PM10 concentration in winter (34.72 μg/m3) was 82% higher than the multiannual average (19.00 μg/m3), and almost three times higher than in summer (11.71 μg/m3). During the winter, PM10 concentration increased by an average of 9.36 μg/m3 due to the increased household heating. Climatological parameters have a demonstrable effect on the PM10 concentration variation. Children, the elderly and men are more sensitive to air pollution, the calculated relative risk for men was (RR = 1.45), and for women (RR = 1.37), respectively. A moderate correlation (0.51) was found between PM10 and pneumonia (P), while a relatively weak correlation (0.39) was demonstrated in the case of PM10 and upper respiratory tract infections (URTI). Furthermore, except thermal humidity index (THI), strong negative correlations were observed between the multiannual monthly mean PM10 and the meteorological data. The PM10 followed a moderate negative correlation with the boundary layer (−0.61). In the case of URTI and P, the highest number of hospital admissions occurred with a 5 to 7-day lag, while the 10 μg/m3 PM10 increase resulted in a 2.04% and 8.28% morbidity increase. For lung cancer (LC) and cardiovascular diseases (AMI, IHD, CCP), a maximum delay of 5–6 months was found. Three-month delay and an average growth of 1.51% was observed in the case of chronic obstructive pulmonary disease (COPD). Overall, these findings revealed that PM10 was and it is responsible for one-third of the diseases.

Nature and sources of ionic species in rainwater during monsoon periods in and around sixteenth-seventeenth century CE monuments in Yamuna River basin, India

The nature and sources of ionic species were studied in the monsoon rainwater collected from two monuments of the sixteenth-seventeenth century CE in the Yamuna River basin from 2016 to 2018. The results showed the acidic pH of the rainwater with high dissolved SO₄^-2 and NO₃^-, and soil-derived components (Ca⁺², Mg⁺², and K⁺). The anionic (SO₄^-2, NO₃^-, Cl^-, F^-, and HCO₃^-) and cationic (Ca⁺², Mg⁺², K⁺, NH₄⁺, and Na⁺) concentrations showed regional differences in yearly contribution mainly from the fossil fuel combustion, soil dust, and farm residue burning. The rainwater analysis showed low dissolved ions at SCTK (Sheikh Chilli's Tomb, Kurukshetra) compared to KBMP (Kabuli Bagh Mosque, Panipat). The mean concentration of SO₄^-2 was 1.5 times higher than the NO₃^- apportioning the sulfate as a dominant acidifying constituent in rainwater. Pearson's correlation and principal component analysis (PCA) showed terrestrial and marine origins of dissolved ions in the rainwater. The Na-normalized molar ratios and the analysis of sea salt and non-sea salt fractions indicate the dominance of non-marine contributions in the precipitation. Based on neutralization factors, cations showed neutralization of rainwater acidity as follows: NF_Ca⁺² > NF_Mg⁺² > NF_NH4⁺ > NF_K⁺. The potential index showed the dominance of the neutralization potential (NP) on acidic potential (AP) at both locations.

Contrasting wet deposition composition between three diverse islands and coastal North American sites

This study examined spatial variations of precipitation accumulation and chemistry for six sites located on the West and East Coasts of the U.S., and one site each on the islands of Hawaii, Bermuda, and Luzon of the Philippines (specifically Manila). The nine coastal sites ranged widely in both mean annual precipitation accumulation, ranging from 40 cm (Mauna Loa, Hawaii) to 275 cm (Washington), and in terms of monthly profiles. The three island sites represented the extremes of differences in terms of chemical profiles, with Bermuda having the highest overall ion concentrations driven mainly by sea salt, Hawaii having the highestSO 4 2 - mass fractions due to the nearby influence of volcanic SO2 emissions and mid-tropospheric transport of anthropogenic pollution, and Manila exhibiting the highest concentration of non-marine ions (NH 4 + non-sea salt [nss]SO 4 2 - , nss Ca2+,NO 3 - , nss K+, nss Na+, nss Mg2+) linked to anthropogenic, biomass burning, and crustal emissions. The Manila site exhibited the most variability in composition throughout the year due to shifting wind directions and having diverse regional and local pollutant sources. In contrast to the three island sites, the North American continental sites exhibited less variability in precipitation composition with sea salt being the most abundant constituent followed by some combination ofSO 4 2 - ,NO 3 - , andNH 4 + . The mean-annual pH values ranged from 4.88 (South Carolina) to 5.40 (central California) withNH 4 + exhibiting the highest neutralization factors for all sites except Bermuda where dust tracer species (nss Ca2+) exhibited enhanced values. The results of this study highlight the sensitivity of wet deposition chemistry to regional considerations, elevation, time of year, and atmospheric circulations.

Rainwater Chemistry Reveals Air Pollution in a Karst Forest: Temporal Variations, Source Apportionment, and Implications for the Forest

Temporal rainwater chemistry was used to reveal air pollution in the Maolan National Karst Forest Park (MNKFP), which is representative of the typical karst forest region of southwest China (SW China). The rainwater ions’ sources, variations, trends, and potential environmental effects were investigated from 2007 to 2010 and from 2013 to 2014. Based on the analysis of the temporal ionic concentrations of rainwater in the MNKFP, significant variations of ions were observed, including in NH4+ (9.7~266.6 μeq L−1) and SO42− (14.5~1396.4 μeq L−1), which were mainly controlled by variations in the source and rainfall amount; a decreased trend of rainwater pH was also observed. Accordingly, NH4+, Ca2+, SO42−, and Cl− were regarded as the most dominant ions. Typical ionic ratios and positive matrix factorization (PMF) model-based source apportionment suggested that anthropogenic inputs (coal combustion, industrial, traffic, and agricultural emissions) contributed 51% of F−, 93% of NO3−, 62% of SO42−, and 87% of NH4+, while the natural sources (crustal dust and sea salt) were the main sources of Cl− (74%), Na+ (82%), K+ (79%), Mg2+ (94%), and Ca2+ (93%). In combination with the reducing neutralization trend of temporal rainwater observed in the MNKFP and the potential effect of rainwater ion deposition on karst forests, more detailed monitoring of the rainfall-related deposition process is required for a better understanding of its potential environmental effects on the Earth’s surface.

Determining rainwater chemistry to reveal alkaline rain trend in Southwest China: Evidence from a frequent-rainy karst area with extensive agricultural production

Rainwater chemistry plays an important role in the earth-surficial ecosystem, but studies on rainwater chemical composition of karst agro-ecosystem are rare. To explore the rainwater alkalization and the provenance of components responsible for neutralization, two-years chemical monitoring of rainwater was carried out in a karst agricultural catchment in Southwest China. The main findings suggest that SO₄^2-, NO₃^-, Ca²⁺, and NH₄⁺ are the principal ions. All the ionic contents show distinctly seasonal variation (highest in winter) in response to variations in seasonal precipitation because the rain-scour process can efficiently remove atmospheric materials. Source identification indicates that Cl^- and Na⁺ are mainly derived from marine input whereas SO₄^2- and NO₃^- are controlled by anthropogenic emission, in particular, fixed emission sources. The source of NH₄⁺ is attributed to intense agricultural production, while Ca²⁺ and Mg²⁺ are mainly derived from calcite dissolution. The rainwater alkalization caused by the seasonal acid neutralization (via basic components, Ca²⁺ and NH₄⁺) is beneficial to crop growth but also reflect agricultural overfertilization. Sulfur controlled the total wet acid deposition (68%-94%) and could be a potential agent of weathering.

Major air pollutants seasonal variation analysis and long-range transport of PM10 in an urban environment with specific climate condition in Transylvania (Romania)

The air quality decrease, especially in urban areas, is related to local-scale conditions and to dispersion of air pollutants (regional and long-range) as well. The main objective of this study was to decipher the seasonal variation of PM10, NO, NO2, NOx, SO2, O3, and CO over a 1-year period (2017) and the possible relationships between air pollution and meteorological variables. Furthermore, trajectory cluster analysis and concentration-weighted trajectory (CWT) methods were used to assess the trajectories and the source-receptor relationship of PM10 in the Ciuc basin Transylvania, known as the "Cold Pole" of Romania. The pollutants show lower concentrations during warmer periods, especially during summer, and significantly higher concentrations were observed on heating season in winter due to seasonal variations in energy use (biomass burning) and atmospheric stability. Subsequently, in February, the highest concentration of PM10 was 132 μg/m3, which is 4 times higher than the highest recorded monthly mean. Our results indicate a negative correlation between CO/temperature (- 0.89), NOx/temperature (- 0.84) and positive between NOx/PM10 (0.95), CO/PM10 (0.9), and NOx/CO (0.98), respectively. Dominant transport pathways were identified and the results revealed that slow-moving southerly (~ 45%) and northwesterly (~ 32%) air masses represent almost 80% and mainly regional flows were discerned. During 2017, increased PM10 levels were measured at the study site when air masses arrived mostly from northwest and southeast. The CWT and polarplot models show a strong seasonal variation and significant differences were observed between weekdays and weekends, namely highest PM10 concentrations during weekends at low wind speed (2-4 m/s).

Chemical characteristics of rainwater in the tropical rainforest region in northwestern Borneo

A comprehensive study of the chemical composition of rainwater was carried out from October 2016 to September 2017 in the equatorial tropical rainforest region of northwestern Borneo. Monthly cumulative rainwater samples were collected from different locations in the Limbang River Basin (LRB) and were later categorized into seasonal samples representing northeast monsoon (NEM), southwest monsoon (SWM), and inter-monsoon (IM) periods. Physical parameters (pH, EC, TDS, DO, and turbidity), major ions (HCO₃^-, Cl^-, Ca²⁺, Mg²⁺, Na⁺, and K⁺) and trace metals (Co, Ni, Cd, Fe, Mn, Pb, Zn, and Cu) were analyzed from collected rainwater samples. Rainwater is slightly alkaline with mean pH higher than 5.8. Chloride and bicarbonate are the most abundant ions, and the concentration of major ions in seasonal rainwater has shown slight variation which follows a descending order of HCO₃^-> Cl^-> Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ in NEM and Cl^- > HCO₃^- > Na⁺ > Ca²⁺ > K⁺ > Mg²⁺ in SWM and Cl^- > HCO₃^- > Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ in IM period. Trace metals such as Fe and Ni have shown dominance in seasonal rainwater samples, and all the metals have shown variation in concentration in different seasons. Variation in chemical characteristic of seasonal rainwater samples identified through piper diagram indicates dominance of Ca²⁺-Mg²⁺-HCO₃^- and mixed Ca²⁺-Mg²⁺-Cl^- facies during NEM, SWM, and IM periods. Statistical analysis of the results through two-way ANOVA and Pearson's correlation also indicates significant variation in physico-chemical characteristics. This suggests a variation in contributing sources during the monsoon seasons. Factor analysis confirmed the source variation by explaining the total variance of 79.80%, 90.72%, and 90.52% with three factor components in NEM, SWM, and IM rainwater samples with different loading of parameters. Enrichment factor analysis revealed a combined contribution of marine and crustal sources except K⁺ which was solely from crustal sources. Sample analysis of backward air mass trajectory supports all these findings by explaining seasonal variation in the source of pollutants reaching the study area. Overall, the results show that the chemical composition of seasonal rainwater samples in LRB was significantly influenced by natural as well as anthropogenic processes. These include (long-range and local) industrial activities, fossil fuel combustion, forest burning, transportation activities including road transport and shipping activities, and land-derived soil dust along with chemical constituents carried by seasonal wind.

Assessment of the Components and Sources of Acid Deposition in Northeast Asia: A Case Study of the Coastal and Metropolitan Cities in Northern Taiwan

In this study, temporal variations, major ion reference indexes, correlation analysis, and statistical data were used to investigate the chemical characteristics of the atmospheric pollutants in wet deposition and reasons for their formation, and further insight into the impact of local and regional atmospheric pollutant distributions on urban and coastal area environments. From November 2014 to October 2015, 158 rainwater samples were collected in coastal Wanli and urban Banqiao of southern Northeast Asia (northern Taiwan). The mean pH of the coastal and urban was 4.63 and 4.58, respectively, lower than the mean (5.31) of 10 East Asia regions during the year of 2015. This was possibly because the concentration of the combined SO42− and NO3− in the study area were greater than the mean of the 10 East Asian regions. This is verified by the calculation of sea-salt fraction (SSF) and non-SSF fraction (NSSF) in study areas, which indicated that Na+ and Cl− accounted for over 85% of the SSF, without Na+ in Banqiao, were mainly due to marine sources. For the NSSF, in addition to SO42− in Wanli, nearly 90% of wet disposition was from SO42− and NO3−, which were emitted from human activities. Furthermore, the analysis of fractional acidity (FA), neutralization factors (NF), neutralization potential (NP), and acidification potential (AP) revealed that acidified precipitation was caused by a lack of neutralizing compounds, which resulted in less neutralization of acidic precipitation. Finally, the results of correlation and principal component analysis (PCA) indicated that because coastal area were geographically closer to the ocean, wet deposition mainly comes from marine sources. However, in urban with a high population density and high traffic quantity, the ions in wet deposition primarily come from anthropogenic activities, such as industrial combustion and vehicle emissions.

Spatial and long-term analysis of rainwater chemistry over the conterminous United States

A comprehensive analysis of the chemical composition of precipitation was performed on rainwater samples collected between 1978 and 2017 over the conterminous US. A total of 86470 data records downloaded from the National Atmospheric Deposition Program were statistically analyzed and assessed in terms of precipitation chemistry. The ion abundance followed the Cl⁻ > Na⁺ > SO₄²⁻ > Ca²⁺ > H⁺ > NH₄⁺ > NO₃⁻ > Mg²⁺ > HCO₃⁻ > K⁺ downward trend, showing that chloride and sodium were the most dominant among anions and cations. Ca²⁺, SO₄^2- and NH₄⁺ concentrations were notable in desert areas or in regions with significant anthropogenic activity. Frequency analysis of pH values showed that the 87.90% of the pH is acidic, exhibiting values under 5.6. According to the acidifying and neutralization potential, rainwater pH is mostly alkaline in the Western region, presenting acidic values in highly industrialized areas, in the Central and Eastern Regions. Fractional acidity showed that in the majority of the studied sampling sites 61% of the acidity in precipitation is neutralized, due to the presence of the main neutralizing agents (NH₄⁺, Ca²⁺, Na⁺), fact sustained by the neutralization factor values. The relationship between acidic and alkaline components was thoroughly examined by ionic ratios and the ammonium availability index. Wet deposition rates of major ions confirmed the dominance of acidic species over neutralizing ones, as well as the significant imprint of regional climate and heavily industrialized areas on the precipitation chemistry. The complex major ion source apportionment, including marine and crustal enrichment factors, sea salt and non-sea salt fractions, Spearman's rank correlation analysis and Principal Component Analysis, showed that anthropogenic influences are the most significant, including coal-fired power plants, oil refineries, major industries and agricultural activities. Crustal and marine sources also presented a prominent imprint on the rainwater chemistry of the conterminous US.

Atmospheric chemical composition of bulk deposition at two geographically distinct locations in Sri Lanka

This study presented the research work carried out for the investigation of chemical composition of bulk precipitation in two geographically and economically distinct areas, namely Gampaha and Kandy Districts. This study was conducted from 2013 to 2014 at three sampling stations in each District. The bulk precipitation was analyzed for pH, conductivity, Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, F^-, Cl^-, NO₃^-, SO₄^2-, Pb, Cu, Mn, Al, Zn and Fe for a total of 375 samples. Only 8% events of acidic precipitation were recorded in Gampaha District when compared with 3% in Kandy District. The volume weighted average concentrations of the major ionic species present in precipitation samples were in the order of Na⁺ > Ca²⁺ > Cl^- > NH₄⁺ > SO₄^2- > Mg²⁺ > NO₃^- > K⁺ > F^- in the Gampaha stations, while the order was NH₄⁺ > Ca²⁺ > Na⁺ > Cl^- > SO₄^2- > Mg²⁺ > NO₃^- > K⁺ > F^- in Kandy District. Neutralization of acidity of precipitation is much more related to CaCO₃ than NH₃, and high content of Ca²⁺ ions present in both Districts strongly supports this fact. When considering marine contribution, SO₄^2-/Na⁺, Ca²⁺/Na⁺ and Mg²⁺/Na⁺ ratios are higher than the reference value suggesting contribution of sources other than marine. Depositions of both Districts show that the concentration of Al is the highest while that of Mn is the lowest. Principal component analysis suggests that influencing human activities on chemical composition of rain water depends on thermal power plant, oil refinery, heavy traffic and waste incineration in the study area.