Daily Precipitation Samples Research Articles

A decade (2008–2017) of water stable isotope composition of precipitation at Concordia Station, East Antarctica

Abstract. A 10-year record of oxygen and hydrogen isotopic composition of precipitation is presented here: from 2008 to 2017, 1483 daily precipitation samples were collected year-round on a raised platform at Concordia Station, East Antarctica. Weather data were retrieved from the Italian Antarctic Meteo-Climatological Observatory automatic weather station (AWS), while ERA5 was used to estimate total precipitation. The δ–temperature relationships were moderately high for daily data (r2=0.63 and 0.64 for δ18O and δ2H, respectively) and stronger using monthly data (r2=0.82 for both δ18O and δ2H), with a slope of about 0.5 ‰ °C−1 for δ18O/TAWS (3.5 ‰ °C−1 for δ2H/TAWS), which remains consistent also using annual averages. The isotopic composition of precipitation is the input signal of the snow–ice system, and this dataset will be useful to improve the interpretation of paleoclimate records and promote a better understanding of the post-depositional processes affecting the isotopic signal in ice cores. This dataset represents a benchmark for the evaluation of isotope-enabled general circulation models. Here, the ECHAM6-wiso output was compared to experimental data, showing moderately good relationships for δ18O and δ2H but not for d-excess, nonetheless marking a substantial improvement from the previous release of the model.

Evidence and causes of recent decreases in nitrogen deposition in temperate forests in Northeast China

High reactive nitrogen (N) emissions due to anthropogenic activities in China have led to an increase in N deposition and ecosystem degradation. The Chinese government has strictly regulated reactive N emissions since 2010, however, determining whether N deposition has reduced requires long-term monitoring. Here, we report the patterns of N deposition at a rural forest site (Qingyuan) in northeastern China over the last decade. We collected 456 daily precipitation samples from 2014 to 2022 and analysed the temporal dynamics of N deposition. NH4+-N, NO3−-N, and total inorganic N (TIN) deposition ranged from 10.5 ± 3.5 (mean ± SD), 6.1 ± 1.6, and 16.6 ± 4.7 kg N ha−1 year−1, respectively. Over the measurement period, TIN deposition at Qingyuan decreased by 55 %, whereas that in comparable sites in East Asia declined by 14–34 %. We used a random forest model to determine factors influencing the deposition of NH4+-N, NO3−-N, and TIN during the study period. NH4+-N deposition decreased by 60 % because of decreased agricultural NH3 emissions. Furthermore, NO3−-N deposition decreased by 42 %, due to reduced NOx emissions from agricultural soil and fossil fuel combustion. The steep decline in N deposition in northeastern China was attributed to reduced coal consumption, improved emission controls on automobiles, and shifts in agricultural practices. Long-term monitoring is needed to assess regional air quality and the impact of N emission control regulations.

Precipitation records of anthropogenic nitrogen pollution in two metropolitan cities of Southeast Asia

Human activities have promoted a rapid and continuous increase in atmospheric nitrogen (N) emission and deposition, resulting in a series of ecological and environmental problems. However, our understanding of N deposition in densely populated tropical regions remains limited, particularly regarding the chemical composition, historical changes, and its association with human activities. In this research, we aim to address these gaps by analyzing concentrations of nitrate (NO3−), ammonium (NH4+) and dissolved organic N (DON) in daily precipitation samples collected in Singapore and Ho Chi Minh City, Vietnam between May 2019 and April 2020. Results reveal that wet N deposition in Singapore and Ho Chi Minh City averaged 31.3 and 30.4 kg N ha−1 yr−1, respectively. Compared to 2001 record, wet N deposition fluxes in Singapore and Hanoi, Vietnam have increased by an average of 78% and 87%, respectively, between 2001 and 2020. Emission data strongly indicate that fossil fuel combustion has significantly elevated both fluxes and chemical composition changes of N deposition in Vietnam. This study provides important observation data of N deposition in tropical urban areas, aiding the assessment of regional N pollution and the management of anthropogenic N emissions in densely populated tropical regions.

Ionic composition of six-year daily precipitation samples collected at JRC-Ispra (Italy) in relation to synoptic patterns and air mass origin

A six-year dataset of daily precipitation samples collected and analyzed at the rural background station of Joint Research Center (JRC) at Ispra (Italy), was studied in conjunction with synoptic patterns and Concentration Weighted Trajectory (CWT) model in order to identify atmospheric mechanisms and transport pathways affecting the concentrations of eight major inorganic ions: NO3−, Cl−, Na+, Mg2+, Ca2+, SO42−, NH4+ and K+. A Principal Component Analysis (PCA) distributed the studied constituents to three categories reflecting major emission sources: a) Anthropogenic b) Sea salt and c) Crustal. The concentrations of all ions in precipitation samples were negatively correlated with precipitation amounts, however the negative correlations were more enhanced for species having a mainly anthropogenic origin (NO3−, SO42−, NH4+ and K+). The anthropogenic constituents were transported mainly from continental Europe, while the primary role of emissions in the industrialized Po Valley was highlighted from the impact of Eastern airflows on NO3−, SO42−, NH4+ and K+ levels. In addition, a secondary Saharan dust source for SO42− was verified. Sea salt species (Cl−, Na+ and Mg2+) were originated from the Mediterranean Sea, the North Sea, the Baltic Sea, and possibly from the Atlantic through France, while Saharan dust intrusions clearly enhanced the levels of crustal constituents (Ca2+ and Mg2+). The elaboration of a multi-year precipitation dataset for the first time with CWT model, provided new insights regarding the emission sources and transport mechanisms affecting the ionic composition of precipitation samples collected at JRC-Ispra.

Variations of Stable Isotopes in Daily Precipitation in a Monsoon Region

The stable isotopes of hydrogen and oxygen in precipitation provide a useful reference for the study of hydrological processes, but concerns have been raised regarding the established patterns in their variations in a monsoon climate zone. In this study, stable isotopes (δ18O and δ2H) of 539 daily precipitation samples from seven hydrometeorological stations in the Beijing area were used to investigate short-term isotopic variations and the controlling factors at a region with a monsoon climate. The δ18O in the precipitation increases from the northwest to the south, which is controlled by the monsoon from the south and continental moisture from the northwest. Consistently, both the high δ18O values and low deuterium excess values from May to September reveal the impact of the monsoon. The amount effect is significant during the monsoon season. In contrast, the T effect is significant, with a gradient of 0.4‰ per °C during the non-monsoon season. A Rayleigh distillation model indicates that the moisture source and residual vapor fraction are the two most important factors in controlling the δ18O patterns in precipitation in a monsoon region, independent of temperature. The result of this study is helpful for the understanding of the regional atmospheric water cycle.

Investigating hydrometeorology of the Western Himalayas: Insights from stable isotopes of water and meteorological parameters

The Himalayas govern the hydrometeorology of the entire Indian subcontinent and feed 19 major rivers on which a large population is dependent. Despite its vast socio-economic relevance, there exist knowledge gaps in the detailed understanding of Himalayan hydrometeorology. The present study attempts to understand subtle hydrometeorological processes concerning precipitation in Western Himalaya (WH), which is further complex due to several mountain ranges in addition to the Great Himalaya and varied land cover. In this backdrop, oxygen and hydrogen isotopic analyses of daily precipitation samples collected from Jammu was done. Major processes and features identified are: (1) Raindrop re-evaporation is dominant, indicated by lower δ18O – δD regression slope (6.6 ± 0.2). (2) Maximum raindrop re-evaporation occurs during Western Disturbances (WD), evident from the low d-excess (<10‰) and high δ18O (>0‰) with low rainfall. (3) Contrary to expectations, negligible moisture is derived from the Mediterranean region (MR) through WD. In contrast, maximum moisture (~97%) is derived from local terrestrial sources, estimated through backward wind trajectories and confirmed by vertical wind velocity (ω) and OLR. (4) The Arabian Sea (AS) moisture contributes more (~11%) compared to the Bay of Bengal (BOB) moisture (~8%) during the monsoon. (5) Isotopically, the most depleted precipitation during July-Aug is associated with continental recycling from the Indo-Gangetic plains and not with the BOB moisture. (6) Isotopic enrichment in precipitation towards end of monsoon is attributed to raindrop re-evaporation, lesser rainout fraction and moisture derived from enriched local sources. (7) Annually, 87% of the moisture for precipitation is derived through continental recycling, and only 13% of the moisture is derived through marine sources (11% from AS and 2% from BOB). Moisture from MR (<0.1%) is negligible.

Convection, Terrestrial Recycling and Oceanic Moisture Regulate the Isotopic Composition of Precipitation at Srinagar, Kashmir

AbstractThe moisture transport and precipitation in the western Himalayas is an interplay of two atmospheric systems: Western Disturbances (WDs) and Indian Summer Monsoon (ISM). WDs primarily transport moisture from the Mediterranean Sea and the Atlantic Ocean, while ISM transports moisture from the Arabian Sea and the Bay of Bengal. Local moisture sources also contribute to the regional precipitation budget. The moisture sources can be distinguished by measuring dual isotopic signatures in precipitation. Oxygen and hydrogen isotopic ratios measured in daily precipitation samples collected at Srinagar, Kashmir from March 2015–April 2017, allowed delineating the role of factors like large‐scale moisture transport processes, and local meteorological factors such as temperature, precipitation amount and relative humidity on the precipitation isotope ratios and its effect on the meteoric water line parameters. Isotopic data were further used to estimate the percentage contributions of distinct moisture sources across different seasons and validation of an isotope enabled general circulation model (iEGCM). We found that the time integrated, large‐scale convection over several days, constitutes a major factor governing the isotopic composition of precipitation, while the role of local meteorological parameters is minimal. A box model to simulate the moisture transport and estimate the oceanic versus terrestrially recycled moisture sources to the regional precipitation reveals Arabian sea to be the key moisture source. Finally, on comparing the observed isotopic composition with iEGCM simulation, discrepancies are noted. Results from the present study will enable improving the interpretation of regional paleo‐climate data derived from various proxy records.

Characteristics of Water-soluble Inorganic Ions in Aerosol and Precipitation and their Scavenging Ratios in an Urban Environment in Southwest China

Daily fine particulate matter (PM2.5) and precipitation samples were collected simultaneously at an urban site in southwest China in four segregated months in 2015 for measuring major water-soluble inorganic ions (WSIIs). Online hourly concentrations of PM10 and PM2.5 were also monitored, which showed annual mean concentrations of 67.8 and 41.6 µg m–3, respectively. PM2.5 showed the highest concentration in winter and lowest in summer. The annual mean concentration of the total WSIIs was 20.3 µg m–3, accounting for about 48.7% of PM2.5. Among the total WSIIs in ambient PM2.5, SO42– was the predominant component (49.7%), followed by NH4+ (24.1%) and NO3– (21.4%). NH4+ and SO42– were the two most abundant ions in precipitation, followed by Ca2+ and NO3–. Seasonal patterns of the major inorganic ions in precipitation were similar to those in PM2.5, with the highest concentration in winter and lowest in summer. The mean scavenging ratios were 454, 445, 364, 456, and 394 for SO42–, NO3–, NH4+, Cl–, and K+, and 116, 353, and 18 for gas SO2, HNO3, and NH3, respectively. The higher scavenging ratios of particulate ions than their gaseous precursors suggest the higher contributions of particles than gases to the total wet deposition.

Origin and percolation times of Milandre Cave drip water determined by tritium time series and beryllium-7 data from Switzerland

Early observations of the tritium (3H) activity in precipitation from Switzerland started in 1967 in Bern and a monitoring program with improved analytical techniques was carried out between 1971 and 2009. Between 2012 and 2015, we performed tritium analyses on daily precipitation samples from north-western Switzerland to better constrain the tritium variability. We also collected waters dripping inside Milandre Cave (Jura Mountains) with a 4–6 months’ resolution in order to estimate the age of the drip water, which is mandatory to interpret the high-resolution speleothem (cave carbonate deposits) records. Over the monitoring period, the mean tritium concentration in the daily precipitation samples was approximately 8.7 ± 4.7 TU with distinct seasonality showing higher values in spring and summer (from April–May to August–September). The similarity in trends with the other cosmogenic radionuclide beryllium-7 (7Be) suggests that, for the study site, tritium in precipitation essentially originates from stratospheric input in spring. In winter, precipitation dynamics with increasing moisture originating from the Atlantic and diluted during transport contribute to low values close to the Atlantic background. In cave drip water, the depleted activity level of tritium indicates a relatively long percolation time from the surface to the cave of several years. A residual superimposed short tritium variability provides evidence for the occurrence of fast flowing water paths. The contribution from both components were quantified based on a two-component lumped parameter-mixing model. Finally, we show that tritium concentrations in cave drip water are linked to the moisture origin and atmospheric transport pathways.

Controls on the isotopic composition of daily precipitation characterized by dual moisture transport pathways at the monsoonal margin region of North-Western India

The Kashmir Valley represents a critical region for understanding isotopic changes in the atmospheric moisture sources since it is located at the intercept between the influences of mid-latitude westerlies and the southwest monsoon circulation. This study presents the variation in isotopic composition (δ18O and δ2H) of daily precipitation samples collected from the Kashmir Valley, North-Western Himalaya, to quantify the effect of meteorological parameters, separately for the Southwest monsoon (SWM) season and the periods of Western Disturbances (WDs). The results suggest that precipitation isotopic composition is strongly modulated by temperature and relative humidity during the periods of WDs. Still, this dependency is weak in the case of the SWM season. Moisture transport pathways calculated from HYSPLIT back trajectory analysis shows a wide spatial variability during the monsoon season. On the other hand, the origin of moisture during the WD season was mostly restricted from the Mediterranean region, providing an explanation of a strong dependency between the precipitation isotopes and the meteorological parameters during the WD period. Such kind of relation may provide additional diagnostic for the WD events and may help in paleo-monsoon investigations.

Isotopic composition of daily precipitation along the southern foothills of the Himalayas: impact of marine and continental sources of atmospheric moisture

Abstract. The flow of the Himalayan rivers, a key source of fresh water for more than a billion people primarily depends upon the strength, behaviour and duration of the Indian summer monsoon (ISM) and the western disturbances (WD), two contrasting circulation regimes of the regional atmosphere. An analysis of the 2H and 18O isotope composition of daily precipitation collected along the southern foothills of the Himalayas, combined with extensive backward trajectory modelling, was used to gain deeper insight into the mechanisms controlling the isotopic composition of precipitation and the origin of atmospheric moisture and precipitation during ISM and WD periods. Daily precipitation samples were collected during the period from September 2008 to December 2011 at six stations, extending from Srinagar in the west (Kashmir state) to Dibrugarh in the east (Assam state). In total, 548 daily precipitation samples were collected and analysed for their stable isotope composition. It is suggested that the gradual reduction in the 2H and 18O content of precipitation in the study region, progressing from δ18O values close to zero down to ca. −10 ‰ in the course of ISM evolution, stems from regional, large-scale recycling of moisture-driven monsoonal circulation. Superimposed on this general trend are short-term fluctuations of the isotopic composition of rainfall, which might have stem from local effects such as enhanced convective activity and the associated higher degree of rainout of moist air masses (local amount effect), the partial evaporation of raindrops, or the impact of isotopically heavy moisture generated in evapotranspiration processes taking place in the vicinity of rainfall sampling sites. Seasonal footprint maps constructed for three stations representing the western, central and eastern portions of the Himalayan region indicate that the influence of monsoonal circulation reaches the western edges of the Himalayan region. While the characteristic imprint of monsoonal air masses (increase of monthly rainfall amount) can be completely absent in the western Himalayas, the onset of the ISM period in this region is still clearly visible in the isotopic composition of daily precipitation. A characteristic feature of daily precipitation collected during the WD period is the gradual increase of 2H and 18O content, reaching positive δ2H and δ18O values towards the end of the period. This trend can be explained by the growing importance of moisture of continental origin as a source of daily precipitation. High deuterium-excess (d-excess) values of daily rainfall recorded at the monitoring stations (38 cases in total, range from 20.6 to 44.0 ‰) are attributed to moisture of continental origin released into the atmosphere during the evaporation of surface water bodies and/or soil water evaporation.

Precipitation isoscapes for New Zealand: enhanced temporal detail using precipitation-weighted daily climatology

ABSTRACTPredictive understanding of precipitation δ2H and δ18O in New Zealand faces unique challenges, including high spatial variability in precipitation amounts, alternation between subtropical and sub-Antarctic precipitation sources, and a compressed latitudinal range of 34 to 47 °S. To map the precipitation isotope ratios across New Zealand, three years of integrated monthly precipitation samples were acquired from >50 stations. Conventional mean-annual precipitation δ2H and δ18O maps were produced by regressions using geographic and annual climate variables. Incomplete data and short-term variation in climate and precipitation sources limited the utility of this approach. We overcome these difficulties by calculating precipitation-weighted monthly climate parameters using national 5-km-gridded daily climate data. This data plus geographic variables were regressed to predict δ2H, δ18O, and d-excess at all sites. The procedure yields statistically-valid predictions of the isotope composition of precipitation (long-term average root mean square error (RMSE) for δ18O = 0.6 ‰; δ2H = 5.5 ‰); and monthly RMSE δ18O = 1.9 ‰, δ2H = 16 ‰. This approach has substantial benefits for studies that require the isotope composition of precipitation during specific time intervals, and may be further improved by comparison to daily and event-based precipitation samples as well as the use of back-trajectory calculations.

The use of Pb, Sr, and Hg isotopes in Great Lakes precipitation as a tool for pollution source attribution

The anthropogenic emission and subsequent deposition of heavy metals including mercury (Hg) and lead (Pb) present human health and environmental concerns. Although it is known that local and regional sources of these metals contribute to deposition in the Great Lakes region, it is difficult to trace emissions from point sources to impacted sites. Recent studies suggest that metal isotope ratios may be useful for distinguishing between and tracing source emissions. We measured Pb, strontium (Sr), and Hg isotope ratios in daily precipitation samples that were collected at seven sites across the Great Lakes region between 2003 and 2007. Lead isotope ratios (207Pb/206Pb=0.8062 to 0.8554) suggest that Pb deposition was influenced by coal combustion and processing of Mississippi Valley-Type Pb ore deposits. Regional differences in Sr isotope ratios (87Sr/86Sr=0.70859 to 0.71155) are likely related to coal fly ash and soil dust. Mercury isotope ratios (δ202Hg=−1.13 to 0.13‰) also varied among the sites, likely due to regional differences in coal isotopic composition, and fractionation occurring within industrial facilities and in the atmosphere. These data represent the first combined characterization of Pb, Sr, and Hg isotope ratios in precipitation collected across the Great Lakes region. We demonstrate the utility of multiple metal isotope ratios in parallel with traditional trace element multivariate statistical modeling to enable more complete pollution source attribution.

Characteristics of total and methyl mercury in wet deposition in a coastal city, Xiamen, China: Concentrations, fluxes and influencing factors on Hg distribution in precipitation

Daily precipitation samples were collected from June 2012 to May 2013 at four observation sites in Xiamen, a coastal city of Southeast China. Concentrations of Total mercury (THg) and methyl mercury (MeHg) in precipitation were rigorously treated and determined. The annual volume-weighted mean concentrations of THg and MeHg at four sites were 12.3 and 0.053 ng L−1, and wet deposition fluxes of THg and MeHg were 14.04 μg m−2 yr−1 and 58.2 ng m−2 yr−1, respectively. MeHg could account for 0.43% of THg, and dissolved Hg contributed 55.4% to THg. There was no significant difference in THg concentration between monsoon and non-monsoon seasons, which was consistent with neither the general seasonal pattern of inland cities of China nor the report from the Gulf coast. Higher wet deposition flux of THg in monsoon season was a function of intense rainfall, whereas higher MeHg flux in non-monsoon season could attribute to increased MeHg concentration. Atmospheric Hg was more efficiently scavenged during the earlier period of the rain event. Positive correlations between precipitation depth and wet deposition fluxes suggested that rainfall played an important role in scavenging atmospheric Hg rather than diluting concentrations. Pearson correlation analysis combined with ions ratios implied that sea salt aerosols had an important impact on rainwater, but coal combustion and traffic emission could be the dominant factors influencing THg in precipitation.

Spatial Patterns in Wet and Dry Deposition of Atmospheric Mercury to Illinois Watersheds

An intensive one month atmospheric mercury monitoring campaign was carried out at 8 sites in central Illinois, USA, during summer of 2011 to assess spatial patterns in wet and dry deposition. Daily precipitation samples, turf surrogate surfaces, and throughfall samples were collected concurrently to measure both wet and dry deposition of mercury, trace metals and major ions. Average deposition values observed for the study period (June 9 to July 3, 2011) for total wet deposition and total dry deposition were 4.0 ± 0.8 µg/m 2 and 1.2 ± 0.4 µg/m 2 , respectively. Based on previous findings, the summer 2011 wet deposition rates were higher compared to summers of 2008 and 2009 at the Nilwood and Peoria sites, and wet deposition during this period represented 20-30% of the annual deposition previously measured. Dry deposition ranged from 17 - 31% of total deposition across sites during the study period. Nilwood and its surrounding monitoring sites had slightly higher wet deposition compared to the more northerly Peoria and surrounding sites.

Sources of mercury in precipitation to Underhill, VT

Daily event precipitation samples were collected from 1995 to 2006 in Underhill, VT, USA and analyzed for mercury (Hg) and trace elements. Over the 12-year period, annual Hg deposition levels at Underhill did not decline significantly despite regulatory efforts to reduce Hg emissions in the United States. Mercury and trace element wet deposition data were examined using the multivariate receptor model EPA PMF 3.0 to identify the sources contributing to Hg deposition at the Underhill site. Results indicate that coal combustion, a mixture of incineration and non-ferrous metal smelting, and a phosphorus source contributed to the observed Hg wet deposition. The model consistently indicated that coal combustion contributed ∼60% of the total Hg measured in wet deposition and the contribution from this source did not change significantly over time. Mercury and trace element deposition were further analyzed using a hybrid-receptor model, quantitative transport bias analysis (QTBA), to identify the likely source locations contributing to Hg deposition. Results from QTBA indicate that the majority of Hg deposition at Underhill is due to transport from the Midwestern United States, where the density of coal-fired utility boilers in the U.S. is largest.

Transit time distributions of a conceptual model: their characteristics and sensitivities

AbstractThe internal behaviour of a conceptual hydrological and tracer transport model, STREAM, has been examined through generation of transit time distributions for the model. The model has been applied to a small sub‐catchment of the Lunan Water in the east of Scotland where daily precipitation and stream water samples have been analysed for isotope content. Transit time distributions are generated by numerically tracking pulse inputs of tracer to the model and evaluating the simulated stream outputs. A set of baseline simulations was first established through calibration to time series of stream flow. A series of model experiments was then undertaken to assess the sensitivity of the simulated transit time distributions to different model parameterizations, flow paths and mixing assumptions. The results of the analysis show that the model transit time distributions do not conform to any simple statistical function and that their characteristics can be significantly altered depending on how the model is set up. The analysis provided valuable insight into the functioning of the model and could be usefully applied to other model codes. Comparison of the transit time distributions generated by conceptual models with data‐based empirical evidence of distributions gives the potential to close the gap in understanding the physical explanation for why catchment systems behave as they do. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Climatic significance of δ18O records from precipitation on the western Tibetan Plateau

Analysis of daily precipitation samples for stable oxygen isotopes (δ18O) collected at the Shiquanhe and Gerze (Gaize, Gertse) stations in the Ngari (Ali) region on the western Tibetan Plateau indicates that air temperature affects the δ18O variations in precipitation at these stations. In summer, Shiquanhe and Gerze show strongly similar trends in precipitation δ18O, especially in simultaneous precipitation events. Moreover, both stations experienced low δ18O values in precipitation during the active monsoon period, resulting from the southwest monsoon (the summer phase of the Indian monsoon). However, during the break monsoon period (during the summer rainy season, when the monsoon circulation is disrupted), δ18O values in summer precipitation remain relatively high and local moisture recycling generally controls the moisture sources. Air temperature correlations with δ18O strengthen during the non-monsoon period (January–June, and October–December) due to continental air masses and the westerlies. In addition, evaporation also influences the δ18O variations in precipitation. The observed temporal and spatial variations of δ18O in precipitation on the western Tibetan Plateau and adjacent regions show that the late May and early June-the late August and early September time frame provides an important period for the transportation of moisture from various sources on the Tibetan Plateau, and that the region of the West Kunlun-Tanggula Ranges acts as a significant climatic divide on the Plateau, perhaps for all of western China.

Influence of air mass origin on the wet deposition of nitrogen to Tampa Bay, Florida—An eight-year study

Rainfall delivers on the average ∼ 10 % of the total annual nitrogen load directly to Tampa Bay, based on precipitation monitoring at a National Atmospheric Deposition Program (NADP) Atmospheric Integrated Research Monitoring Network (AIRMoN) site located adjacent to Tampa Bay in urban Tampa. We coupled the chemical analyses for 606 daily precipitation samples collected from 1996 to 2004 with corresponding air mass trajectory information to investigate if wet-deposited nitrogen originated from near versus removed source regions. Air mass trajectories were obtained using the National Oceanic and Atmospheric Administration (NOAA) HYbrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model, and were classified into six trajectory categories by the direction of their approach to Tampa Bay. Rainfall nitrate and ammonium concentrations were significantly lower for over-water air mass trajectories than for over-land trajectories as expected, but contributed to 40% of the total wet-deposited nitrogen, a likely consequence of the higher frequency of rain events for these trajectories. Average rainfall nitrate concentrations were significantly higher for air masses that stagnated over the urbanized bay region. We estimated that local sources contributed 1 kg N ha - 1 yr - 1 or 25% of the total inorganic nitrogen wet-deposited to Tampa Bay.

Sources of Mercury Wet Deposition in Eastern Ohio, USA

In the fall of 2002, an enhanced air monitoring site was established in Steubenville, Ohio as part of a multi-year comprehensive mercury monitoring and source apportionment study to investigate the impact of local and regional coal combustion sources on atmospheric mercury deposition in the Ohio River Valley. This study deployed advanced monitoring instrumentation, utilized innovative analytical techniques, and applied state-of-the-art statistical receptor models. This paper presents wet deposition data and source apportionment modeling results from daily event precipitation samples collected during the calendar years 2003-2004. The volume-weighted mean mercury concentrations for 2003 and 2004 were 14.0 and 13.5 ng L(-1), respectively, and total annual mercury wet deposition was 13.5 and 19.7 microg m(-2), respectively. Two new EPA-implemented multivariate statistical models, positive matrix factorization (PMF) and Unmix, were applied to the data set and six sources were identified. The dominant contributor to the mercury wet deposition was found by both models to be coal combustion (approximately 70%). Meteorological analysis also indicated that a majority of the mercury deposition found at the Steubenville site was due to local and regional sources.