Anthropogenic inputs of boron into urban atmosphere: Evidence from boron isotopes of precipitations in Guiyang City,China

Boron (B) concentrations and isotopic compositions were measured in the precipitations of Guiyang, China for one year. Most precipitation samples have boron concentrations of from 2.1 to 4.8 ng ml^?1, and δ¹¹B values of from +2.0‰ to +30.0‰. Boron concentrations and δ¹¹B values of heavy rain samples are generally higher than those of light rain and snow samples. Anthropogenic inputs provided most of the SO₄^2? and NO₃^?, which were predominant ions in the precipitation. The major cation Ca²⁺ in the precipitation was mainly originated from local dust.The total boron in precipitation from Guiyang is explained by the mixing model of three boron sources. Assuming a δ¹¹B value of +45‰ for the seawater component, contributions of marine source, organic matter and biomass combustion, and coal combustion were estimated to be 32%, 49%, and 19%, respectively to the total boron in Guiyang precipitations. The coal combustion and biomass (and/or organic matter) combustion showed different contributions of boron to the rainwaters in different seasons, the former in cold season while the latter in summer season had a more marked influence on the chemical and isotopic composition of the rainwater. The largest contribution of seawater-originated boron was observed for the heavy rain samples, which was up to 68%. This study indicates that the atmospheric environment of Guiyang city was strongly influenced by human activities, and boron isotopic composition is of great sensitivity to anthropogenic sources and can be a powerful technique to trace various sources of atmospheric emissions and even their origins.     

Rainwater formaldehyde: concentration,deposition and photochemical formation

Formaldehyde (HCHO) concentrations were measured in 116 rain samples in Wilmington, NC from June 1996 to February 1998. Concentrations ranged from below the detection limit of 10 nM, to 13 μM, in the range of HCHO levels reported at other locations worldwide. The volume-weighted annual average rainwater formaldehyde concentration was 3.3±0.3 μM and comprised approximately 3% of the measured dissolved organic carbon. Using the volume weighted average HCHO concentration and annual precipitation of 1.4 m, an annual formaldehyde deposition of 4.6 mmol m⁻² yr⁻¹ was determined. Rainwater is a significant source of formaldehyde to surface waters and may contribute as much as 30 times the resident amount found in natural waters of southeastern North Carolina during the summer. Formaldehyde concentrations did not correlate with precipitation volume suggesting continuous supply during rain events. Evidence is presented which indicates part of this supply may be from direct photochemical production in the aqueous phase. Formaldehyde levels exhibited a distinct seasonal oscillation, with higher concentrations during the summer. This pattern is similar to that observed with other rainwater parameters at this site including pH, nitrate, and ammonium, and is most likely the result of increased photochemical production, as well as biogenic and anthropogenic emissions during summer months. The concentration of formaldehyde in both winter El Nino rains and summer tropical rains was less than half its concentration in non-El Nino or non-tropical events, suggesting significant terrestrial input. Formaldehyde was correlated with hydrogen peroxide and non-sea-salt sulfate deposition suggesting a relationship between HCHO, H₂O₂, S(VI) within the troposphere.     

Scavenging of sea-salt aerosols by rain events over Arabian Sea during ARMEX

Scavenging coefficients are obtained for sea-salt particles at rainfall intensity of 5, 10, 15, 20 and 45 mm h⁻¹. Evolutions of size distributions for sea-salt particles by precipitation scavenging are simulated using theoretically estimated scavenging coefficients. Results indicate that below-cloud scavenging affects mainly sea-salt particles in coarse mode. Observed concentrations of Na⁺ and Cl⁻ in rainwater increased with rainfall intensity and aerosol size. Comparison of predicted concentrations of Na⁺ and Cl⁻ in rainwater with observed ionic concentrations of short-timed wet-only samples collected during rain events on 2 August 2002 over Arabian Sea (ARMEX-2002) supports the model result.     

Diurnal variations in major rainwater components at a coastal site in North Carolina

Concentrations of several major rainwater components were determined in rain events occurring during the early morning hours (12:00 midnight to 6:00 a.m.) and during the afternoon (12:00 noon to 6:00 p.m.) to examine possible diurnal variations. Generally, rainwater components with gas phase origins (H⁺, NO₃⁻, formaldehyde, H₂O₂, formic acid, acetic acid, pyruvic acid, oxalic acid, and lactic acid) had higher concentrations during p.m. rain events compared to a.m. events. Although source strengths of both biogenic and anthropogenic rainwater components are generally higher during the daytime, nocturnal removal of a wide variety of components in similar proportions (approximately 2–3× less at night) indicates a physical rather than a chemical process affecting diurnal variations. Rainwater components with aerosol origins (Cl⁻, and SO₄²⁻) displayed the opposite diurnal pattern or showed no diurnal variation. Possible reasons for these variations include one or both of the following scenarios: (1) the formation of dew at night removes gas phase atmospheric gasses but not aerosols or (2) during the night, a marine air mass containing lower concentrations of all analytes and higher concentrations of Cl⁻ is advected into the area.     

Factors affecting the levels of hydrogen peroxide in rainwater

Measurements of hydrogen peroxide (H₂O₂) and several meteorological and chemical parameters were made for 34 rain events which occurred in Miami, Florida between April, 1995 and October, 1996. The measured H₂O₂ concentrations ranged from 0.3 to 38.6 μM with an average concentration of 6.9 μM. A strong seasonal dependence for H₂O₂ concentrations was observed during this period, with highest concentrations in the summer and lower levels in the winter, which corresponds to the stronger solar radiation and higher vaporization of volatile organic compounds (VOCs) in the summer and fall, and the weaker sunlight and lower vaporization in the winter and spring. Measurements also showed a significant increase trend of H₂O₂ with increasing ambient rainwater temperature. Rains that were out from lower latitude were exposed to higher solar irradiation and contained relatively higher levels of H₂O₂ than those from the north. All these observations indicate that photochemical reactions that involved volatile organic compounds are the predominant source of H₂O₂ observed in rainwater. During several individual rainstorms, H₂O₂ concentration was found to increase as a function of time due to electrical storm activities. This finding suggests that lightning could be an important factor that determines the level of H₂O₂ during thunderstorms. Statistical data showed that the highest concentrations of H₂O₂ were observed only in rains containing low levels of nonsea-salt sulfate (NSS), nitrate and hydrogen ion. H₂O₂ concentrations in continental originated rains were much lower than marine originated ones, indicating that air pollutants in continental rains could significantly deplete the H₂O₂ concentration in atmospheric gas-phase, clouds and rainwater.     

Real-time wet scavenging of major chemical constituents of aerosols and role of rain intensity in Indian region

Real-time simultaneous studies on chemical characteristics of rainwater and PM₁₀ aerosols were carried out to understand the scavenging of major chemical components in Indian region. The concentrations of Ca²⁺, NH₄⁺, SO₄²⁻ and NO₃⁻ were observed to be lower in the aerosol samples collected during rain as compared to before and after rain events. The most significant reduction was noticed for Ca²⁺ (74%) during rain which showed highest scavenging ratio (SR) and indicated that below-cloud scavenging is an effective removal process for Ca²⁺ in Indian region. Among non-sea salt components, Ca²⁺ had highest SR at Hyderabad indicating typical characteristics of crustal influence as abundance of calcium carbonate in soil dust has been reported in India. However, the levels of these major chemical components gradually got build-up in due course of time. After rain events, the levels of SO₄²⁻ aerosols were noticed to be substantially higher (more than double) within 24 h. In general, scavenging ratios for all components (except Ca²⁺, NH₄⁺ and K⁺) were higher over BOB as compared to Hyderabad. The maximum fall in aerosol levels (BR minus AR) was observed during continuous and low intensity rain events that did not allow building up of aerosol concentrations.     

Water-soluble organic nitrogen in atmospheric aerosol: a comparison of UV and persulfate oxidation methods

Two well established methods that are widely applied in the determination of marine dissolved organic nitrogen (DON) have been investigated in their application to the determination of rainwater DON and the water-soluble organic nitrogen component of atmospheric aerosol. Empirical observation highlighted some difficulties in the analysis of DON in these non-marine matrices, so some practical suggestions for the extension of the oxidative methods to atmospheric samples are proposed.Ten rain samples, 20 aqueous aerosol extracts, and a suite of commercially obtained organic nitrogen compounds were both chemically oxidised by persulfate and oxidised by exposure to high-intensity ultraviolet light. The total dissolved nitrogen concentration of the rains in this study ranged from 4 to 35 μM nitrogen. The aerosol extracts were diluted to a pre-oxidation concentration range of 12–65 μM N for oxidation and analysis. Both UV and persulfate methods require the aqueous extract of the aerosol organic nitrogen to be diluted approximately to rainwater concentrations for optimal oxidation efficiency, since sub-optimal recoveries and high analytical variability arise at high concentration. Some potential causes of analytical interference at higher concentration are discussed.This study shows that total dissolved nitrogen results obtained by the two methods are linearly correlated (with an R² of 0.87 for 30 samples) over the full range of natural rainwater concentrations, but results obtained using the persulfate oxidation are about 30% lower than those obtained by photo-oxidation.     

Application of the nested grid STEM to an early summer acid rain in South Korea

The nested grid Sulfur Transport Eulerian Model (STEM) was developed and used to simulate the acid rain in Korea that occurred on 10 June 1996. The present nested grid system consists of three-grid systems. The coarsest grid system includes China, Korean Peninsula and Japan with the horizontal grid size of 80 km and the finest grid system includes only Korea with the horizontal grid size of 8.9 km. The calculated gas-phase SO₂ and O₃ concentrations agree relatively well with the field measurements. In addition, the model successfully reproduces the measured sulfate and nitrate concentrations in the rain water and futhermore identified the high concentration regions of liquid-phase sulfate and nitrate. In the present simulation conditions, most of the gas-phase of SO₂ and HNO₃ were washed out. A close relationship between wet deposition fluxes and precipitation rates were found for sulfate and nitrate. Finally, the model results also showed that a fine grid size is required to accurately calculate gas-phase concentrations as well as acid deposition fluxes.     

Chemical composition and seasonal variation of acid deposition in Guangzhou, South China: comparison with precipitation in other major Chinese cities

With the aim of understanding the origin of acid rains in South China, we analyzed rainwaters collected from Guangzhou, China, between March 2005 and February 2006. The pH of rainwater collected during the monitoring period varied from 4.22 to 5.87; acid rain represented about 94% of total precipitation during this period. The rainwater was characterized by high concentrations of SO₄²⁻, NO₃⁻, Ca²⁺, and NH₄⁺. SO₄²⁻ and NO₃⁻, the main precursors of acid rain, were related to the combustion of coal and fertilizer use/traffic emissions, respectively. Ca²⁺ and NH₄⁺ act as neutralizers of acid, accounting for the decoupling between high SO₄²⁻ concentrations and relatively high pH in the Guangzhou precipitation. The acid rain in Guangzhou is most pronounced during spring and summer. A comparison with acid precipitation in other Chinese cities reveals a decreasing neutralization capacity from north to south, probably related to the role and origin of alkaline bases in precipitation.     

Influence of air mass trajectories on the chemical composition of precipitation in India

Chemical composition of precipitation was measured with wet-only samplers at a rural site at Bhubaneswar in eastern India during 1997–1998. All rain events were compared with trajectories and precipitation fields from the ECMWF. The pH and ionic concentrations were found to vary systematically with the origin of air and the amount of rainfall along the trajectory. A seasonal cycle for pH was found with a monthly median pH below 5.0 during October–December. The highest monthly median concentration of Ca²⁺ was found in May with 20 μmol l⁻¹ and for SO₄²⁻ in January with 52 μmol l⁻¹. Samples with trajectories within 400 km from Bhubaneswar during the last 5 days were found to have a median pH slightly below 5.0 as an average. These samples also had the highest concentration for all measured ions, indicating large pollution sources within the region. Samples with continental origin showed a decrease of ∼70% in concentration if there had been rain during >50% of the last 5 days compared to rain during <50% of the last 5 days. High concentrations of Na⁺ and Cl⁻ were also found in continental samples. Resuspension of previously deposited sea salt is believed to be the reason. The data were compared with data from three other sites in western India and higher concentrations of almost all ions (NH₄⁺ being the exception) compared to Bhubaneswar were found at the west coast in monsoon samples.     

Polycyclic aromatic hydrocarbons in rainwater and surface waters of Lake Maggiore, a subalpine lake in Northern Italy

Fourteen polycyclic aromatic hydrocarbons (PAHs) were measured in surface waters and precipitation inputs to Lake Maggiore, a subalpine lake in Northern Italy, from July 2003 to January 2004. Particulate and dissolved phases in surface water and rain samples were determined. Analyses of PAHs were performed using XAD-2 resin to isolate the dissolved PAHs and subsequent extraction by accelerated solvent extraction (ASE). Both the dissolved and particulate phase PAH patterns in surface water and rainwater samples were dominated by the low molecular weight compounds (e.g., phenanthrene, fluoranthene and pyrene). More than 85% of PAHs in surface waters and 72% of PAHs in rainwater were associated to the dissolved phase. The SigmaPAH concentrations in surface waters (particulate and dissolved phases) were 0.584 +/- 0.033 ng l(-1), 2.9 +/- 0.312 ng l(-1) and in rainwater (particulate and dissolved phases) 27.5 +/- 2 ng l(-1), 75.4 +/- 9 ng l(-1), respectively. Temporal variability of PAH concentrations in rain and surface water samples were observed, with higher concentrations in November and December, coinciding with the largest precipitation amounts. The comparison of PAH signatures in rainwater and surface waters seems to indicate that wet deposition (2.5-41 microg m(-2) month(-1)) is the main source of PAH contamination into surface waters of Lake Maggiore.     

Assessing decadal changes in rainwater alkalinity at a rural Mediterranean site in the Montseny Mountains (NE Spain)

Annual volume-weighted mean (VWM) concentrations in rainwater collected at La Castanya (LC, Montseny Mountains, NE Spain) were analysed from 1983 to 2000 to study the temporal trends in precipitation chemistry, and the causes behind the changes. A significant positive correlation was found between annual rainwater SO₄²⁻ concentrations at LC and Spanish SO₂ emissions (r=0.73, P=0.0008) both decreasing remarkably during this period. Rainwater alkalinity increased during the period, shifting from negative values at the beginning (VWM in the 5 initial years=−2.7 μeq l⁻¹) to alkaline values in recent years (VWM in the 5 final years=18.0 μeq l⁻¹). Stepwise regression analysis indicated that 88% of the variation of alkalinity could be accounted for by the variability of non-marine Ca²⁺ and non-marine SO₄²⁻, with a more prominent dependence on Ca²⁺.Rains of African provenance were highly enriched in alkalinity and Ca²⁺, but no significant increases in their occurrence were found for the study period. Because of the reported higher dust updraft in northern Africa during years of high North Atlantic Oscillation (NAO) index, we also explored the relationship between rainwater variables associated with an African provenance and NAO. Annual precipitation was inversely related to NAO (r=−0.61, P=0.007). The annual wet deposition of African dust-related elements showed no correlation with NAO, probably because wet deposition of these elements depends on two factors (precipitation and dust updraft) which have opposite behaviour with respect to NAO. We hypothesise that dry deposition of African dust during dry spells (not sampled in this study) might be higher during high NAO-index years.     

Pesticides analysed in rainwater in Alsace region (Eastern France): Comparison between urban and rural sites

Current-used pesticides commonly applied in Alsace region (Eastern France) on diverse crops (maize, vineyard, vegetables, etc.) were analysed, together with Lindane, in rainwater between January 2002 and June 2003 simultaneously on two sites situated in a typical rural (Erstein, France) and urban area (Strasbourg, France).Rainwater samples were collected on a weekly basis by using two automatic wet only collectors associated with an open collector for the measurement of rainwater height.Pesticides were analysed by GC-MSMS and extracted from rainwater by SPME. Two runs were performed. The first one was performed by using a PDMS (100 μm) fibre for pesticides where direct injection into GC is possible (alachlor, atrazine, azinphos-ethyl, azinphos-methyl, captan, chlorfenvinphos, dichlorvos, diflufenican, α- and β-endosulfan, iprodione, lindane, metolachlor, mevinphos, parathion-methyl, phosalone, phosmet, tebuconazole, triadimefon and trifluralin). The second run was performed by using PDMS/DVB fibre and this run concerns pesticides where a preliminary derivatisation step with pentafluorobenzylbromide (PFBBr) is required for very low volatiles (bromoxynil,2,4-MCPA, MCPP and 2,4-D) or thermo labiles (chlorotoluron, diuron and isoproturon) pesticides.Results showed that the more concentrated pesticides detected were those used as herbicides in large quantities in Alsace region for maize crops (alachlor, metolachlor and atrazine). Maximum concentrations for these herbicides have been measured during intensive applications periods on maize crops following by rapid decrease immediately after use.For Alachlor, most important peaks have been observed between 21 and 28 April 2003 (3327 ng L⁻¹ at Erstein and 5590 ng L⁻¹ at Strasbourg). This is also the case for Metolachlor where most important peak was observed during the same week.Concentrations of pesticides measured out of application periods were very low for many pesticides and some others where never detected during this period. This is the case for diflufenican which was detected only during application. Two important peaks of concentrations were observed; a first one (101 ng L⁻¹) in Erstein in November 2002 (4–11 November) and a second one (762 ng L⁻¹) also in Erstein (28 April–15 May).The same behaviour can be seen for chlorfenvinphos and phosalone which have been detected, respectively, 2 and 4 times in Erstein and Strasbourg at high concentrations (28 April 2003–15 May 2003, 187 ng L⁻¹ of phosalone and 157 ng L⁻¹ of chlorfenvinphos in Erstein).MCPP, 2,4 MCPA and 2,4-D have been detected at high concentrations in rainwater but for the other pesticides very episodically and mainly during their use in agriculture. Maximal concentrations of MCPP and 2,4 MCPA have been measured in Erstein between 28 April and 15 May (904 and 746 ng L⁻¹, respectively).Comparison between rural and urban sites showed that concentrations in rural areas are generally higher except for pesticides commonly applied in urban areas like Diuron.No seasonal phenomenon was observed for Diuron. This herbicide has been detected in practically all of the rainwater samples in Strasbourg (40/41) with a maximum of 1025 ng L⁻¹ (16–23 September 2002) in 38 samples on 41 in Erstein with a maximum of 317 ng L⁻¹ (15–23 October 2002). The total concentration of Diuron measured between 4 March 2002 and 20 July 2003 is of 4721 ng L⁻¹ in Strasbourg and 5025 ng L⁻¹ in Erstein. This result shows that wet deposition of Diuron in urban and rural sites was equivalent and can be explained by the “urban use” of this molecule together with its potential persistence.     

Chemical and strontium isotope characterization of rainwater in Beijing,China

Major ion concentrations and Sr isotope ratios (⁸⁷Sr/⁸⁶Sr) were measured in rainwater samples collected at an urban site in Beijing over a period of one year. The pH value and major ion concentrations of samples varied considerably, and about 50% of the rainwater studied here were acidic rain with pH values less than 5.0. Ca²⁺ and NH₄⁺ were the dominant cations in rainwaters and their volume weighted mean (VWM) values were 608 μeq l^?1 (14–1781 μeq l^?1) and 186 μeq l^?1 (48–672 μeq l^?1), respectively. SO₄^2? was the predominant anion with VWM value of 316 μeq l^?1 (65–987 μeq l^?1), next was NO₃^? with VWM value of 109 μeq l^?1 (30–382 μeq l^?1).Using Na as an indicator of marine origin, and Al for the terrestrial inputs, the proportions of sea salt and terrestrial elements were estimated from elemental ratios. More than 99% of Ca²⁺ and 98% of SO₄^2? in rainwater samples are non-sea-salt origin. The ⁸⁷Sr/⁸⁶Sr ratios were used to characterize the different sources based on the data sets of this study and those from literatures. Such sources include sea salts (⁸⁷Sr/⁸⁶Sr～0.90917), soluble soil dust minerals originating from either local or the desert and loess areas (～0.7111), and anthropogenic sources (fertilizers, coal combustion and automobile exhausts). The high concentrations of alkaline ions (mainly Ca²⁺) in Beijing atmosphere have played an important role to neutralize the acidity of rainwater. However, it is worth noting that there is a remarkable acidification trend of rainwater in Beijing recent years.     

Seasonal variability of formaldehyde production from photolysis of rainwater dissolved organic carbon

Photochemical production of formaldehyde (HCHO) was measured in rainwater from 13 precipitation events in Wilmington, North Carolina, USA under conditions of simulated sunlight. HCHO concentrations increased in all samples irradiated with no changes observed in dark controls. HCHO photoproduction rates were strongly correlated with dissolved organic carbon (DOC) suggesting HCHO was derived from direct or indirect photolysis of rainwater DOC. The higher photoproduction rates (0.03–2.9 μM h^?1) relative to those reported for surface waters suggests that rainwater DOC is more photolabile in terms of HCHO production than surface waters. HCHO photoproduction rates were higher in growing season (1.0 ± 1.0 μM h^?1) compared to non-growing season (0.08 ± 0.05 μM h^?1) even when rates were normalized for DOC (6.8 ± 3.6 μM h^?1 mM C^?1 versus 1.8 ± 1.0 μM h^?1 mM C^?1). The higher growing season rate may be related to seasonal differences in the composition of DOC as evidenced by differences in fluorescence per unit carbon of rainwater samples. Irradiation of C18 extracts of rainwater also produced HCHO, but at lower rates compared to corresponding whole rain samples, suggesting that hydrophyllic components of rainwater play a role in HCHO photoproduction. Our results indicate that photolysis of rainwater DOC produces significant amounts of HCHO, and possibly other low molecular weight organic compounds, likely increasing its reactivity and bioavailability.     

Copper complexation in coastal rainwater,southeastern USA

Complexation of dissolved copper (Cu) was studied in Atlantic coastal rainwater using adsorptive cathodic stripping voltammetry (ASCV) with salicylaldoxime as a competing ligand at pH 7.8. Detectable concentrations of strong Cu-complexing ligands possessing conditional stability constants of 10¹³–10¹⁶ were observed in over 80% of the rain events occurring over the course of 2 year. In 11 of the 23 samples analysed, total dissolved Cu concentrations were higher than those of dissolved ligands, indicating that a significant fraction of the Cu occurred as the free ion and as weaker complexes. In the remaining samples, ligand concentrations were equal to or greater than Cu concentrations, indicating virtually complete (>99%) complexation of the ambient Cu. By varying the analytical detection window, two classes of ligands with differing conditional stability constants were detected in selected rain samples suggesting that the Cu ligands most likely represent a spectrum of organic compounds. Back trajectory analysis indicated that continentally dominated rain samples contained higher concentrations of Cu and organic ligands relative to storms of marine origin, suggesting a strong terrestrial and/or anthropogenic source of both Cu and ligands in rain at this location. Variability in Cu speciation may impact a variety of atmospheric redox reactions because free and complexed forms of the metal have very different reactivities.     

Dissolved organic carbon in rainwater: Glassware decontamination and sample preservation and volatile organic carbon

The efficiency of different methods for the decontamination of glassware used for the analysis of dissolved organic carbon (DOC) was tested using reported procedures as well as new ones proposed in this work. A Fenton solution bath (1.0 mmol L⁻¹ Fe²⁺ and 100 mmol L⁻¹ H₂O₂) for 1 h or for 30 min employing UV irradiation showed to combine simplicity, low cost and high efficiency. Using the optimized cleaning procedure, the DOC for stored UV-irradiated ultra-pure water reached concentrations below the limit of detection (0.19 μmol C L⁻¹). Filtered (0.7 μm) rain samples maintained the DOC integrity for at least 7 days when stored at 4 °C. The volatile organic carbon (VOC) fraction in the rain samples collected at two sites in São Paulo state (Brazil) ranged from 0% to 56% of their total DOC content. Although these high-VOC concentrations may be derived from the large use of ethanol fuel in Brazil, our results showed that when using the high-temperature catalytic oxidation technique, it is essential to measure DOC rather than non-purgeble organic carbon to estimate organic carbon, since rainwater composition can be quite variable, both geographically and temporally.     

On the interpretation of event and sub-event rainfall chemistry

Variations in precipitation chemistry between and within rain events have been examined in order to identify possible relationships with synoptic, mesoscale and micrometeorological processes. A microprocessor-based acid rain monitor was used to provide high resolution meteorological and rain chemistry data from which two case study events have been selected to illustrate event and sub-event rainfall chemistry characteristics. Event rainfall chemistry is strongly influenced by the history of the prevailing air mass and the synoptic situation. From back trajectories calculated at the 950 mbar level it is clear that air mass history can change markedly within a few hours. These observations emphasise the value of high resolution rainfall chemistry measurements. Pollutant concentrations in rainwater have been shown to fluctuate markedly within the course of individual events as a result of both advective and scavenging processes. Advective effects may result from: (a) air mass discontinuities at frontal zones; and/or (b) variable rainfall interception of the air mass prior to arrival at the site. A simple mathematical model has been developed to describe the scavenging mechanisms and it shows good agreement with field observations. Theoretical considerations suggest that in-cloud processes give rise to most of the observed decline in concentrations.     

Carbonyl compounds and dissolved organic carbon in rainwater of an urban atmosphere

This study investigates the occurrence of carbonyl compounds in rainwater at the city of Thessaloniki, Northern Greece. The concentrations of carbonyl compounds (as sum of 14 compounds) ranged from 21.8 to 592 μg/L, mean concentration 119 μg/L. Formaldehyde, acetaldehyde, hexanal, glyoxal, and methylglyoxal were the dominant compounds. DOC concentrations in rainwater ranged from 0.46 to 21.3 mg/L. UV–Vis and fluorescence spectra characteristics showed variation among rain events. Carbonyl compounds were negatively correlated with temperature exhibited relatively higher concentrations in cold season. They also influenced by storm origin with higher concentrations under terrestrial air masses. Calm conditions enhance the concentrations of DOC. Wash out is an effective removal mechanism of DOC.     

Iron speciation and hydrogen peroxide concentrations in New Zealand rainwater

Rain was collected on the southern portion of the South Island of New Zealand during the summer of 1999 (January–March) during which time significant losses of ozone and increased UV were reported in the stratosphere over New Zealand. Iron and hydrogen peroxide concentrations were measured in rainwater because these analytes are directly influenced by photochemical processes and therefore are particularly susceptible to increasing UV levels. The absolute concentration of dissolved Fe(II) in New Zealand samples was very similar to summertime rain received in Wilmington, NC however the relative contribution of Fe(II) to total Fe was approximately twice as great in New Zealand samples. The larger percentage of reduced iron may reflect higher UV levels in New Zealand since Fe(II) is generated via photochemical reduction of particulate or dissolved Fe(III). No dissolved Fe(III) was detected in New Zealand rainwater, in contrast to the Wilmington site, where summertime Fe(III) concentrations are approximately equal to Fe(II) concentrations. Summertime hydrogen peroxide concentrations and diel variability in New Zealand were similar to other coastal and marine values in both the northern and southern hemispheres suggesting the increasing UV in New Zealand is not significantly increasing hydrogen peroxide concentrations at this location. Any excess photochemically produced hydrogen peroxide in New Zealand may be consumed through oxidation of Fe(II) which is rapidly reformed from photochemical reduction of Fe(III) by the higher UV levels in New Zealand.