The temporal and spatial variability of scavenging ratios for NSS sulfate, nitrate, methanesulfonate and sodium in the Atmosphere over the North Atalantic Ocean

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.

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.

Seven-year study of monsoonal rainwater chemistry over the mid-Brahmaputra plain, India: assessment of trends and source regions of soluble ions

This work is a 7-year study of monsoonal rainwater chemistry (n = 302), over mid-Brahmaputra plain during 2012 to 2018. The samples were analyzed for major chemical parameters viz. pH, electrical conductivity (EC), and ions (SO₄^2-, NO₃^-, Br^-, Cl^-, F^-, Mg²⁺, Ca²⁺, K⁺, NH₄⁺, Na⁺, and Li⁺) to assess the chemistry. The mean pH of rainwater varied among the years, which was maximum in 2018 (6.18 ± 0.72) and minimum in the year 2014 (5.39 ± 0.54), and the variations were significant at p < 0.0001. Ridgeline plots were drawn to visualize interannual variations, which revealed that Ca²⁺ was the dominant cation in the early years, whereas NH₄⁺ prevailed in the latter years. Mann-Kendall analysis and Sen's slope statistical tests were employed, and it was found that all the ions showed positive S values indicating increasing trends. Enrichment factors (EF) of K⁺, SO₄^2-, and NO₃^- were found to be high with respect to both soil and seawater suggesting the influence of emissions from fossil fuel and biomass burning in the chemistry of rainwater. Principal component analysis (PCA) was applied to identify the sources of rain constituents, and five factors were obtained explaining crustal dust, biomass burning, fossil fuel combustion, agricultural emissions, and coal burning as possible sources. Airmass back trajectory clusters and Potential Source Contribution Function (PSCF) were computed by application of HYbrid Single-Particle Lagrangian Integrated Trajectory model to appreciate the terrestrial influence on the chemistry. The results indicated inputs from both local and regional dust and anthropogenic constituents that influenced the monsoonal rainwater chemistry over Brahmaputra Valley.

Aerosol responses to precipitation along North American air trajectories arriving at Bermuda

North American pollution outflow is ubiquitous over the western North Atlantic Ocean, especially in winter, making this location a suitable natural laboratory for investigating the impact of precipitation on aerosol particles along air mass trajectories. We take advantage of observational data collected at Bermuda to seasonally assess the sensitivity of aerosol mass concentrations and volume size distributions to accumulated precipitation along trajectories (APT). The mass concentration of particulate matter with aerodynamic diameter less than 2.5 μm normalized by the enhancement of carbon monoxide above background (PM2.5/ΔCO) at Bermuda was used to estimate the degree of aerosol loss during transport to Bermuda. Results for December-February (DJF) show that most trajectories come from North America and have the highest APTs, resulting in a significant reduction (by 53 %) in PM2.5/ΔCO under high-APT conditions (> 13.5 mm) relative to low-APT conditions (< 0.9 mm). Moreover, PM2.5/ΔCO was most sensitive to increases in APT up to 5 mm (-0.044 μg m-3 ppbv-1 mm-1) and less sensitive to increases in APT over 5 mm. While anthropogenic PM2.5 constituents (e.g., black carbon, sulfate, organic carbon) decrease with high APT, sea salt, in contrast, was comparable between high- and low-APT conditions owing to enhanced local wind and sea salt emissions in high-APT conditions. The greater sensitivity of the fine-mode volume concentrations (versus coarse mode) to wet scavenging is evident from AErosol RObotic NETwork (AERONET) volume size distribution data. A combination of GEOS-Chem model simulations of the 210Pb submicron aerosol tracer and its gaseous precursor 222Rn reveals that (i) surface aerosol particles at Bermuda are most impacted by wet scavenging in winter and spring (due to large-scale precipitation) with a maximum in March, whereas convective scavenging plays a substantial role in summer; and (ii) North American 222Rn tracer emissions contribute most to surface 210Pb concentrations at Bermuda in winter (~75 %-80 %), indicating that air masses arriving at Bermuda experience large-scale precipitation scavenging while traveling from North America. A case study flight from the ACTIVATE field campaign on 22 February 2020 reveals a significant reduction in aerosol number and volume concentrations during air mass transport off the US East Coast associated with increased cloud fraction and precipitation. These results highlight the sensitivity of remote marine boundary layer aerosol characteristics to precipitation along trajectories, especially when the air mass source is continental outflow from polluted regions like the US East Coast.

Multiple isotopic tracing for sulfate and base cation sources of precipitation in Hangzhou city, Southeast China: Insights for rainwater acidification mechanism

Acid deposition has been regarded as a serious factor in the deteriorative water environment and ecosystems. Despite the powerful acid emission control measures have been implemented by the Chinese government, many areas (especially Southeast China) are still suffering from acid deposition. The chemical and isotopic (δ³⁴S and ⁸⁷Sr/⁸⁶Sr) compositions of rainwater in Hangzhou, a typical megacity in Southeast China with serious acid rain problem, for one year were studied with the aim to better constrain potential sources and explore the causes of rainwater acidification. Most rainwater samples were acidic, with a VWM pH value of 4.65. SO₄^2- was the dominant anion and the main acid ion in rainwater. Sulfur isotope and the quantity equilibrium model revealed that sea salt, crustal, biogenic, and anthropogenic sulfur represented 2.3%, 0.1%, 16.7%, and 80.8% of the SO₄^2- source in rainwater, respectively. The back trajectory and strontium isotopes indicated that the base cations (BCs) in rainwater originated mainly from anthropogenic sources. The relatively low neutralizing capacity caused by limited BCs input and emission control measures undermines some efforts to reduce rainwater acidity. This case study demonstrated that a valuable tool to probe the source of acid rain and unravel the mechanism of rainwater acidification can be provided by multiple lines of evidence, including rainwater chemical compositions, stable sulfur isotopes, and stable strontium isotopes.

Atmospheric deposition of inorganic nutrients to the Western North Pacific Ocean

We evaluated the potential impacts of atmospheric deposition on marine productivity and inorganic carbon chemistry in the northwestern Pacific Ocean (8-39°N, 125-157°E). The nutrient concentration in atmospheric total suspended particles decreased exponentially with increasing distance from the closest land-mass (Asia), clearly revealing anthropogenic and terrestrial contributions. The predicted mean depositional fluxes of inorganic nitrogen were approximately 34 and 15 μmol m^-2 d^-1 to the west and east of 140°E, respectively, which were at least two orders of magnitude greater than the inorganic phosphorus flux. On average, atmospheric particulate deposition would support 3-4% of the net primary production along the surveyed tracks, which is equivalent to ~2% of the dissolved carbon increment caused by the penetration of anthropogenic CO₂. Our observations generally fell within the ranges observed over the past 18 years, despite an increasing trend of atmospheric pollution in the source regions during the same period, which implies high temporal and spatial variabilities of atmospheric nutrient concentration in the study area. Continued atmospheric anthropogenic nitrogen deposition may alter the relative abundances of nitrogen and phosphorus.

An Aerosol Climatology and Implications for Clouds at a Remote Marine Site: Case Study Over Bermuda

Aerosol characteristics and aerosol-cloud interactions remain uncertain in remote marine regions. We use over a decade of data (2000-2012) from the NASA AErosol RObotic NETwork, aerosol and wet deposition samples, satellite remote sensors, and models to examine aerosol and cloud droplet number characteristics at a representative open ocean site (Bermuda) over the Western North Atlantic Ocean (WNAO). Annual mean values were as follows: aerosol optical depth (AOD) = 0.12, Ångström Exponent (440/870 nm) = 0.95, fine mode fraction = 0.51, asymmetry factor = 0.72 (440 nm) and 0.68 (1020 nm), and Aqua-MODIS cloud droplet number concentrations = 51.3 cm-3. The winter season (December-February) was characterized by high sea salt optical thickness and the highest aerosol extinction in the lowest 2 km. Extensive precipitation over the WNAO in winter helps contribute to the low FMFs in winter (~0.40-0.50) even though air trajectories often originate over North America. Spring and summer had more pronounced influence from sulfate, dust, organic carbon, and black carbon. Volume size distributions were bimodal with a dominant coarse mode (effective radii: 1.85-2.09 μm) and less pronounced fine mode (0.14-0.16 μm), with variability in the coarse mode likely due to different characteristic sizes for transported dust (smaller) versus regional sea salt (larger). Extreme pollution events highlight the sensitivity of this site to long-range transport of urban emissions, dust, and smoke. Differing annual cycles are identified between AOD and cloud droplet number concentrations, motivating a deeper look into aerosol-cloud interactions at this site.

Trace Elements and Their Variation with pH in Rain Water in Arid Environment

Climate change in Kuwait has resulted in temperature fluctuations, frequent dust storms, and noticeable changes in the amount of precipitation. Pollutants released into the atmosphere from various sources affect the chemical composition of rainwater and impact its usability. The present study on rainwater focused on the determination of trace elements, sources, and their variation with respect to change in temperature and pH. The samples were collected from 12 different locations in both industrial and urban regions during significant rain events (n = 31) from November 2018 to March 2019 and samples were analyzed for trace elements in ICP-OES using standard USEPA 200.7 method. The mean concentration of the 16 elements analyzed followed the trend: Co < Cd < Cr < Mo < V<Ni < Pb < As < Se < Fe < Cu < Mn < Zn < Al < Ba < Sr and were inferred to be within the WHO permissible limits of drinking water. The analytical results revealed that Strontium (Sr) had the highest mean concentration (188 μg/L) followed by barium (Ba), aluminum (Al), and zinc (Zn) with mean concentrations of 95.2 μg/L, 30.4 μg/L, and, 16.6 μg/L respectively. The sources of contamination in rainwater were identified by calculating the enrichment factor (EF) using element concentration reported in Kuwait dust and from continental crustal values. EF for Fe, V, Ni, and Cr were below 10, indicating purely crustal sources. Ni, Zn, Cu, and Mn exhibited values between 10 and 100, reflecting industrial sources of contamination. EF for Sr was greater than 100, due to inputs from anthropogenic sources. A strong association between Al and pH along with correlation between Sr, Cr, Cu, Ni, Mo, V, and meteorological parameters was revealed from statistical analysis. Furthermore, pH Redox Equilibrium C programming (PHREEQC) was used to simulate changes in pH and temperature in rainwater to predict the resultant variations in trace element concentrations. There was no significant change observed in pH with rise in temperature, but the concentration of trace elements varied with change in pH. The concentration of V, Cr, and Al were most sensitive to pH variations. The results indicated that industrial emissions, fuel combustion, and dust in Kuwait are the primary sources of Al, Sr, Mn, Zn, and Ba in the rainwater samples. Since, the concentrations of these elements are relatively low, rainwater in Kuwait could be harvested for drinking and domestic purposes and used for recharging aquifers.

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.

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 Research Over the Western North Atlantic Ocean Region and North American East Coast: A Review of Past Work and Challenges Ahead

Decades of atmospheric research have focused on the Western North Atlantic Ocean (WNAO) region because of its unique location that offers accessibility for airborne and ship measurements, gradients in important atmospheric parameters, and a range of meteorological regimes leading to diverse conditions that are poorly understood. This work reviews these scientific investigations for the WNAO region, including the East Coast of North America and the island of Bermuda. Over 50 field campaigns and long-term monitoring programs, in addition to 715 peer-reviewed publications between 1946 and 2019 have provided a firm foundation of knowledge for these areas. Of particular importance in this region has been extensive work at the island of Bermuda that is host to important time series records of oceanic and atmospheric variables. Our review categorizes WNAO atmospheric research into eight major categories, with some studies fitting into multiple categories (relative %): Aerosols (25%), Gases (24%), Development/Validation of Techniques, Models, and Retrievals (18%), Meteorology and Transport (9%), Air-Sea Interactions (8%), Clouds/Storms (8%), Atmospheric Deposition (7%), and Aerosol-Cloud Interactions (2%). Recommendations for future research are provided in the categories highlighted above.

Assessment of the toxic potential of rainwater precipitation: First evidence from a case study in three Greek cities

Considering the necessity to monitor rainwater quality and the limited existing data regarding wet precipitations' toxic potential, the toxic potential of rainwater (RW) samples collected in three cities of Western Greece (Corfu, Agrinion and Patras) during May, October, November, and December of 2014 were investigated. The relationship of the adverse effects obtained, against cytokinesis block micronucleus (CBMN) and Vibrio fischeri bioluminescence (Microtox) assays with the physicochemical characteristics, the heavy metal concentration levels of rainwater samples and the meteorological parameters governing the climatic conditions in each region, were studied in detail. All samples showed pH values in the range of 5.37-7.17, high concentrations of ΝΗ₄⁺ and the presence of SO₄^2- and NO₃^-. The metals Al, Mn, Fe, Co, Ni, Cu, Zn, As, Sb, Cd, were detected in most of the samples, with maximum concentrations ranging from 0.16 μg L^-1 (for Co) to 86.6 μg L^-1 (for Fe). The CBMN assay showed statistically significant rainwater cytotoxic activity at 5% (v/v) concentration in all cities during all months studied and at 10% (v/v) in Agrinion and Corfu in May. No genotoxic effect was induced at 5% (v/v) concentration of rainwater, except for Corfu city during November, whereas 10% (v/v) of rainwater led to statistically significant increase in micronuclei frequencies in all three cities. The highest (100%) and the lowest (14%) inhibitory effect exhibited by the rainwater in the Vibrio test were noticed at Corfu city during May and December, respectively. Considering the inter-relations obtained among the abiotic and biotic variables measured in all cases, conductivity, SO₄^2-, NH₄⁺, and total metal burden could be related with both CBMN and Microtox assays data, regardless of the site- and month-specific differences. The multidisciplinary approach presented here showed that the physicochemical profile of rainwater precipitation could be significantly related with the induction of adverse effects on biota.

Acid neutralization of precipitation in Northern China

There is an increasing concern over the impact of human-related emissions on the acid precipitation in China. However, few measurements have been conducted so far to clarify the acid-neutralization of precipitation on a regional scale. Under a network of 10 sites across Northern China operated during a 3-year period from December 2007 to November 2010, a total of 1118 rain and snow samples were collected. Of this total, 28% was acid precipitation with pH < 5.6. Out of these acid samples, 53% were found heavily acidic with pH value below 5.0, indicating significantly high levels of acidification of precipitation. Most of the acidity of precipitation was caused by H2SO4 and HNO3, their relative contribution being 72% and 28%, respectively. However; the contribution of HNO3 to precipitation acidity will be enhanced due to the increasing NO(x) and stable SO2 emissions in future. Neutralization factors for K+, NH4+, Ca2+, Na+, and Mg2+ were estimated as 0.06, 0.71, 0.72, 0.15, and 0.13, respectively. The application of multiple regression analysis further quantified higher NH4+ and Ca2+ contribution to the neutralization process, but the dominant neutralizing agent varied from site to site. The neutralization was less pronounced in the rural than urban areas, probably due to different levels of alkaline species, which strongly buffered the acidity. Presence of high concentrations of basic ions was mainly responsible for high pH of precipitation with annual volume-weighted mean (VWM) values larger than 5.6 at several sites. It was estimated that in the absence of buffering ions, for the given concentration of SO4(2-) and NO3-, the annual VWM pH of precipitation would have been recorded around 3.5 across Northern China. This feature suggested that emissions of particles and gaseous NH3 played very important role in controlling the spatial variations of pH of precipitation in the target areas.

Characterization of rain and roof drainage water quality in Xanthi, Greece

Thirteen field campaigns were undertaken in the period from December 2,2002 until September 1,2004 to collect water samples in order to characterize the quality of rainfall and roof drainage in the city of Xanthi, a typical provincial city in Greece. In each campaign, water samples were collected from 10 representative sites in the city (in total 130 samples), representing areas of distinct land use and human activities (i.e., traffic volume, residence density and industrial activity). The water samples were analyzed according to drinking water criteria for total coliform (not detected), temperature (range: 0.9-20 degrees C), pH (range: 3.6-11.4), alkalinity (range: 0-21.5 mg CaCO(3)/L), nitrate (range: 0-2456 microg/L), ammonium (range: 0-2628 microg/L), sulfate (range: 0-0.5 mg/L), calcium (range: 259.1-3064 microeq/L), magnesium (range: 0.8-488.8 microeq/L), potassium (range: 0.0-110.6 microeq/L) and dissolved heavy metals (Fe, range: 0.01-0.18 mg/L; Mn, range: 0.01-0.09 mg/L; Zn, range: 0.01-0.54 mg/L; Cu, Cr and Ni, not detected). Pollutant concentrations were generally higher in roof drainage than in rainwater, but both were lower than drinking water standards. Dissolved heavy metal concentrations were generally higher in the areas of intensive human activities, such as roads with high traffic volume and densely populated residential areas. The satisfactory quality of rainwater, which results from this analysis, makes its use as grey water possible.

Chemical characterization of rainwater at Singapore

A short term study of the chemical composition of rainwater was carried out from November 1999 to October 2000 in Singapore. The rainwater was typically acidic with a mean pH of 4.2. Sulfate was the most abundant ion and comparable to the results reported for other industrialized regions. The concentrations of major ions (NH(4)(+), Ca(2+), K(+), Na(+), Mg(2+), SO(4)(2+), NO(3)(2-), Cl(-), HCOO(-), CH(3)COO(-)) varied monthly. Results show that local meteorological conditions influence the chemical compositions to a significant extent. The pollutants in rainwater were derived from long range and local (industry and traffic) sources.