Source apportionment of rainwater chemical composition to investigate the transport of lower atmospheric pollutants to the UTLS region

Significant influence of urban human activities and marine input on rainwater chemistry in a coastal large city, China

The coastal urban region is generally considered an atmospheric receptor for terrestrial and marine input materials, and rainfall chemistry can trace the wet scavenging process of these materials. Fast urbanization in China's east coastal areas has greatly altered the rainwater chemistry. However, the chemical variations, determinants, and sources of rainfall are unclear. Therefore, the typical coastal city of Fuzhou was selected for 1-year rainwater sampling and inorganic ions were detected to explore above problems. The findings depicted that rainwater ions in Fuzhou were slightly different from those in other coastal cities. Although NO3-, SO42-, Ca2+ and NH4+ dominated the rainwater ions, the marine input Cl- (22 %) and Na+ (11 %) also contributed a considerable percentage to the rainwater ions. Large differences in ion concentrations (2∼28 times) were found in monthly scale due to the rainfall amount. Both natural and anthropogenic determinants influenced the rainwater ions in coastal cities, such as SO2 emission, air SO2 and PM10 content on rainwater SO42-, NO3-, and Ca2+, and soot & dust emission on rainwater SO42-, NO3-, indicating the vital contribution of human activities. Stoichiometry and positive matrix factorization-based sources identification indicated that atmospheric dust/particles were the primary contributor of Ca2+ (83.3 %) and F- (83.7 %), and considerable contributor of SO42- (39.5 %), NO3- (38.3 %) and K+ (41.5 %). Anthropogenic origins, such as urban waste volatilization and fuel combustion emission, contributed 95 % of NH4+, 54.5 % of NO3- and 41.9 % of SO42-, and the traffic sources contribution was relatively higher than fixed emission sources. The marine input represented the vital source of Cl- (77.7 %), Na+ (84.9 %), and Mg2+ (55.3 %). This work highlights the significant influence of urban human activities and marine input on rainwater chemicals and provides new insight into the material cycle between the atmosphere and earth-surface in coastal city.

Atmospheric precipitation chemistry and environmental significance in major anthropogenic regions globally

In order to investigate the spatiotemporal distribution and influencing factors of global precipitation chemistry, we conducted a comprehensive analysis using multiple data sources, revealing the impact of human activities on the natural environment. The results indicate a decreasing trend in global precipitation acidity over the past 20 years. The distribution of global precipitation is influenced by both natural and anthropogenic factors. Alkaline cation concentrations are higher in desert and arid regions, while high concentrations of SO42- and NO3- are primarily found in industrial areas, and agricultural areas exhibit higher NH4+ concentrations. Coastal regions have higher Na+ and Cl- concentrations compared to inland areas. However, the increased Na + and Cl- concentrations due to inland salinization should not be overlooked. Additionally, influenced by atmospheric circulation, transboundary pollution from South Asia leads to higher SO42- and NO3- concentrations in precipitation over the Tibetan Plateau. Meteorological factors have a weaker influence on precipitation chemistry compared to geographical and human activity factors, although ion concentrations in snowfall are higher than in rainfall.

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.

Is the atmospheric boundary layer altitude or the strong thermal inversions that control the vertical extent of aerosols?

It is well known that the atmospheric boundary layer (ABL) plays a significant role in controlling the variability of atmospheric constituents such as aerosols and trace-gases. Hence, significant diurnal and seasonal variation in these will be observed as the ABL altitude does. However, on several occasions, high aerosol concentration in the lidar measurements is observed even above the ABL altitude. This raised a question that up to what extent ABL altitude acts as a capping layer for these pollutants? From the detailed analysis carried out using long-term (2010-2018) lidar observations and simultaneous radiosonde profiles obtained from Gadanki, India, we show that 'there exist thermal inversions (TI), which are stronger than the ABL inversions, that fully control the vertical extent'. The detailed characteristics of TI (inversion strength (IS) and inversion depth (ID)) are also obtained. The results revealed that aerosol concentrations below the TI altitude increases with IS (ID) up to 3-4 K (300-400 m) during winter whereas in pre-monsoon it increases up to 2-3 K (100-200 m). Thus, IS of up to 2-4 K is required to fully trap the aerosol concentrations and this TI coincide with the ABL inversions for 51.7% only, particularly during the winter and pre-monsoon seasons. This analysis is further extended to different geographical locations of India using the aerosol profiles obtained from CALIPSO and a network of 23 radiosonde stations. The observed results provided further evidence that the vertical distribution of aerosols is restricted to the maximum extent by the TI but not the ABL altitude. These observations lead us to propose a hypothesis that 'trapping of aerosols fully occurs up to particular IS and ID only and the ABL altitude is not the deciding factor most of the time for capping the aerosol vertical distribution'. These findings will greatly help in modeling the diffusion and transport of air pollutants in the lower troposphere.

Hurricane/tropical storm rainwater chemistry in the US (from 2008 to 2019)

Rainwater chemistry of extreme rain events is not well characterized. This is despite an increasing trend in intensity and frequency of extreme events and the potential excess loading of elements to ecosystems that can rival annual loading. Thus, an assessment of the loading imposed by hurricane/tropical storm (H/TS) can be valuable for future resiliency strategies. Here the chemical characteristics of H/TS and normal rain (NR) in the US from 2008 to 2019 were determined from available National Atmospheric Deposition Program (NADP) data by correlating NOAA storm tracks with NADP rain collection locations. It found the average pH of H/TS (5.37) was slightly higher (p < 0.05) than that of NR (5.12). On average, H/TS events deposited 14% of rain volume during hurricane season (May to October) at affected collection sites with a maximum contribution reaching 47%. H/TS events contributed a mean of 12% of Ca²⁺, 22% of Mg²⁺, 18% of K⁺, 25% of Na⁺, 7% of NH₄⁺, 6% of NO₃^-, 25% of Cl^- and 11% of SO₄^2- during hurricane season with max loading of 77%, 62%, 94%, 65%, 39%, 34%, 64% and 60%, respectively, which can lead to ecosystems exceeding ion-specific critical loads. Four potential sources (i.e., marine, soil dust, agriculture and industry/fossil fuel) were indicated by PCA. The positive matrix factorization (PMF) suggested Mg²⁺, Na⁺ and Cl^- were primarily marine-originated in both event types, while 36% more sea-salt Ca²⁺ and 33% more sea-salt SO₄^2- were deposited during H/TS. Agriculture and industry/fossil fuel were the main sources of NH₄⁺ and NO₃^-, respectively, in both rain event types. However the NH₄⁺ contribution from industry/fossil fuel increased by 13% during H/TS indicating a potential vehicle source associated with emergency evacuations. This work provides a comprehensive assessment of the rainwater chemistry of H/TS and insight to expected ecosystem loading for future extreme events.

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.

Phase-wise analysis of the COVID-19 lockdown impact on aerosol, radiation and trace gases and associated chemistry in a tropical rural environment

Phase-wise variations in different aerosol (BC, AOD, PM₁, PM_2.5 and PM₁₀), radiation (direct and diffused) and trace gases (NO, NO₂, CO, O₃, SO₂, CO₂ and CH₄) and their associated chemistry during the COVID-19 lockdown have been investigated over a tropical rural site Gadanki (13.5° N, 79.2° E), India. Unlike most of the other reported studies on COVID-19 lockdown, this study provides variations over a unique tropical rural environment located at a scientifically strategic location in the Southern Indian peninsula. Striking differences in the time series and diurnal variability have been observed in different phases of the lockdown. The levels of most species that are primarily emitted from anthropogenic activities reduced significantly during the lockdown which also impacted the levels and diurnal variability of secondary species like O₃. When compared with the same periods in 2019, short-lived trace gas species such as NO, NO₂, SO₂ which have direct anthropogenic emission influence have shown the reduction over 50%, whereas species like CO and O₃ which have direct as well as indirect impacts of anthropogenic emissions have shown reductions up to 10%. Long-lived species (CO₂ and CH₄) have shown negligible difference (<1%). BC and AOD have shown reductions over 20%. Particulate Matter (1, 2.5 and 10) reductions have been in the range of 40 to 50% when compared to the pre-lockdown period. The changes in shortwave downward radiation at the surface, diffuse component due to the scattering and diffuse fraction have been +2.2%, -4.1% and -2.4%, respectively, in comparison with 2019. In contrast with the studies over urban environments, air quality category over the rural environment remained same during the lockdown despite reduction in pollutants level. All the variations observed for different species and their associated chemistry provides an excellent demonstration of rural atmospheric chemistry and its intrinsic links with the precursor concentrations and dynamics.

Towards a model for aerosol removal by rain scavenging: The role of physical-chemical characteristics of raindrops

A one-year study was carried out in León, Spain, in order to characterize physically and chemically the precipitation. With the aim of studying the scavenging process of atmospheric pollutants, scavenging ratio and removal coefficients were calculated through physical parameters of raindrops (obtained by disdrometer data) and through chemical properties of aerosols. Finally, linear models for the prediction of the chemical composition of rainwater and the efficiency of the removal effect were established. In general, the rainwater was dominated by NH₄⁺ > SO₄^2- > NO₃^- in all seasons. Higher ion concentrations and conductivity and lowest pH were observed in summer, due to the low volume of rain. In winter, the high values of Na⁺ and Cl^- in the rainwater showed the contribution from marine sources, while in summer the high concentrations of Ca²⁺, Mg²⁺, SO₄^2-, NH₄⁺ and NO₃^- reflected the contribution from both crustal and anthropogenic sources. The linear models revealed that the amount of dissolved organic carbon and of the water-soluble ions in rain samples, Ca²⁺, SO₄^2-, NO₃^-, increases with the volume swept by the falling drops. Insoluble carbon fraction has a negative dependence with the volume swept and positive with the diameter of the raindrop. Removal coefficients are affected by the concentration in the air of each species before precipitation, the duration of the event and the time elapsed between two precipitation events.

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.

Characterization of precipitation in the background of atmospheric pollutants reduction in Guilin: Temporal variation and source apportionment

Rainfall samples were collected from three observation sites in Guilin from 2013 to 2017, and the chemical composition characteristics of precipitation and the contribution made by different ion sources were analyzed when atmospheric pollutants levels were reduced. The results showed that acid gas emissions and atmospheric pollutant concentrations continued to decline during the study period. However, the change in the volume-weighted mean pH at the three sites suggested that acid rain pollution was not alleviated and began to deteriorate after 2015. The continuing downward trend for alkaline neutralizing ions (Ca²⁺, NH₄⁺) in precipitation indicated that the reduction in alkaline neutralizing substances in the atmosphere was an important factor that led to the deterioration in acid rain across Guilin. The principal component analysis and spearman correlation analysis indicated five sources of ions in precipitation. Quantitative assessment of these five sources indicated that fossil fuel combustion contributed the most ions concentration in precipitation at the three sites, followed by agriculture, terrestrial (crustal) sources, marine sources, and biomass burning. Long-distance airflow might affect the acidity, the electrical conductivity (EC), and ion concentrations in precipitation across Guilin. The airflow trajectory from the west and southeast directions corresponded to higher acidity and ion concentrations. According to the current air pollution control strategy planned by Guilin, reducing atmospheric coarse particles and NH₃ at the same time may potentially lead to further deteriorations in acid rain contents. Therefore, Guilin needs to develop more reasonable pollution prevention measures that synergistically control atmospheric pollutants and acid rain pollution.

Chemistry and Microbiology of Urban Roof Runoff in Kraków, Poland with Ecological and Health Risk Implications

Urban rainwater samples, collected in various districts of Kraków during the period from the spring of 2019 to the winter of 2020, were investigated, and relevant risk implications were assessed. The contents of 31 components were determined, including: bacteria, fungi, pH, EC, Cl-, N-NO3, P-PO4, SO42-, SiO2, K, Mg, Ag, Al, Ba, Ca, Cu, K, Mg, Mo, Na, Pb, Sb, and Zn. The highest contents of the investigated elements were determined in the industrial (eastern) part of Kraków. The values of toxicity potential were <1, indicating a lack of ecological risk. The value of contamination degree indicated moderate rainwater contamination in all analyzed elements (Cdeg = 9.44). The total non-carcinogenic risk values, in both adults (hazard quotient (HQ) = 1.38) and children (HQ = 2.54), exceeded the acceptable level of one. Regarding individual elements in dermal contact, the acceptable level of 1 × 10−6 was exceeded in Pb (adults carcinogenic risk (CR) = 4.87 × 10−5, children CR = 2.23 × 10−5). The contents of the analyzed chemical compounds did not exceed the permissible levels adopted for drinking water; however, rainwater was significantly contaminated with respect to its microbiological parameters. Rainwater was suitable for non-potable use.

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.

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.