Acute and Chronic Toxicity of Chlorine Dioxide (ClO2) and Chlorite (ClO2ˉ) to Rainbow Trout (Oncorhynchus mykiss) (4 pp)

Goal, Scope and Background Chlorite (ClO2ˉ) is a primary decomposition product when chlorine dioxide (ClO2) is added during water treatment; therefore the toxic effects of both compounds on aquatic organisms are possible. Limited data are available concerning their toxicity to fish. The aim of this study was to investigate sensitivity of rainbow trout to acute and chronic toxicity of chlorine dioxide and chlorite, and to estimate the Maximum-Acceptable-Toxicant-Concentration (MATC) of those compounds in fish. Methods The acute and chronic toxicity of chlorine dioxide and chlorite to larval and adult rainbow trout was investigated in 96-hour to 20-day laboratory exposures evaluating the wide range spectrum of biological indices under semi-static conditions. Results and Discussion Median lethal concentration (96-hour LC50) values derived from the tests were: 2.2 mg/l for larvae; 8.3 mg/l for adult fish and 20-day LC50 for larvae was 1.6 mg/l of chlorine dioxide, respectively. Chlorite was found to be from 48 to 18 times less acutely toxic to larvae and adult fish, correspondingly. Both chemical compounds induced similar toxic effects in rainbow trout larvae during chronic tests (they affected cardio-respiratory and growth parameters), but chlorine dioxide had a higher toxic potency than chlorite. A significant decrease in the heart rate and respiration frequency of larvae was established. However, within an increase in exposure duration recovery of cardio-respiratory responses was seen to have occurred in larvae exposed to chlorite. Meanwhile, in larvae exposed to chlorine dioxide, a significant decrease in cardio-respiratory responses remained during all 20-day chronic bioassays. Chlorine dioxide also more strongly affected growth parameters of rainbow trout larvae at much lower test concentrations. Decreased rate of yolk-sack resorption occurred only in the tests with chlorine dioxide. Conclusions Maximum-Acceptable-Toxicant-Concentration (MATC) of 0.21 mg/l for chlorine dioxide and of 3.3 mg/l for chlorite to fish was derived from chronic tests based on the most sensitive parameter of rainbow trout larvae (growth rate). According to substance toxicity classification accepted for Lithuanian inland waters, chlorine dioxide and chlorite can be referred to substances of \moderate\ toxicity to fish. Recommendations and Outlook Due to its very reactive nature, chlorine dioxide is rapidly (in a few hours) reduced to chlorite, which is persistent also as a biocide but 16 times less toxic to fish, according to MATC. Therefore, it is much more likely that fish will be exposed to chlorite than to chlorine dioxide in natural waters. Presently accepted, the Maximum-Permitted-Concentration of total residual chlorine (TRC) in waste-water discharging into receiving waters is 0.6 mg/l. If this requirement will not be exceeded, it is unlikely that fish would be exposed to lethal or even to sublethal concentrations of chlorine dioxide or chlorite. Furthermore, chlorine dioxide does not generate toxic nitrogenous (chloramines) or carcinogenic organic residuals (trihalomethanes). All these properties make chlorine dioxide a more promising biocide than chlorine.     

Determination and evaluation of cadmium, lead and nickel in greenhouse soils of Almería (Spain)

This study determines total levels of three (Cd, Pb and Ni) potentially toxic trace elements in western Almería (Spain) greenhouse surface soil horizons using microwave digestion; it establishes the geochemical baseline concentration, and it investigates possible relationships between soil properties and elemental concentrations. The results show that the soil concentration of these heavy metals is lower than mentioned in the European and Spanish normative, but they are higher than those reported by other authors working on agricultural soils. The obtained geochemical baseline concentrations (mg kg(-1)) were: Cd 0.4-0.8, Pb 2.5-89.9 and Ni 16.1-30.7. Using the upper baseline criterion, 88% of greenhouse soils have relatively higher content of heavy metals because of their Cd, Pb and Ni concentration. Moreover, soil properties are related to heavy metals contents suggesting that among Cd, Pb and Ni have a similar origin and those total metal concentrations are controlled primarily by soil compositions.     

Concentrations of heavy metal and radioactivity in surface water and sediment of Hazar Lake (Elaziğ, Turkey)

Concentration of heavy metals and natural gross radioactivity were measured in the surface water and sediment of Hazar Lake (Elazi?, Turkey). Eight sampling sites were pre-defined in different locations of the lake. A preliminary study on heavy metals (Zn, Fe, Mn, Ni, Cu, Cr, Co and Pb), major elements (Na, K, Ca, Mg) concentrations and natural radioactivity related to 226Ra, gross-alpha and gross-beta radiations in the surface water and deep sediments were determined. The obtained results showed that, in general, the heavy metals (Zn, Fe, Mn, Ni, Cu and Pb) and major elements (Na, K, Ca, Mg) concentrations in water did not exceed WHO (World Health Organization, 1999), EC (Europe Community, 1998), EPA (Environment Protection Agency, 2002) and TSE-266 (Turkish Standard, 1997) guidelines. Generally, heavy metals and major elements concentration of the sediments were found decrease in sequence of Fe>Mg>Ca>Mn>Zn>Ni>Cr>Cu>Co>Pb. The results of this study indicated that a general absence of serious pollution in the Hazar Lake. The results obtained from the radioactivity determination indicate that the surface water radioactivity concentration of 226Ra, gross-alpha and gross-beta were ranging from 0.52+/-0.02 to 2.02+/-0.06 Bq/l and from 0.65+/-0.03 to 2.52+/-0.07 Bq/l and from 0.01+/-0.01 to 0.14+/-0.01 Bq/l, respectively. Deep sediment radioactivity concentrations of 226Ra is ranging from 0.07+/-0.03 to 0.32+/-0.07 Bq/g.     

Sources and concentrations of gaseous and particulate reduced nitrogen in the city of Münster (Germany)

Atmospheric ammonia mixing ratios and the main inorganic ions NH₄⁺, NO₃⁻ and SO₄²⁻ of size-resolved particles in the range from 0.05 to 10 μm were measured at an urban site in Münster, Germany. High mixing ratios of ammonia with a median of 5.2 ppb and a maximum of 50 ppb were detected. The mass fraction of submicron particles was much higher during the day than at night. At night, a greater particle mass and an increased presence of particulate nitrate was measured. Recurring patterns of particle distribution were distinguished and their characteristics analysed. In half of the measurements, the accumulation mode was clearly dominating, which is an indication of aged aerosol. In some measurements, higher concentrations of fine particles were found indicating particle formation. In these cases, a smaller particle mass and about four times greater ratios of ammonia versus ammonium concentrations were observed. These data show that ammonia contributes considerably to the formation of secondary particulate material.     

Removal of copper from water by electrocoagulation process—effect of alternating current (AC) and direct current (DC)

Purpose and aim

In general, direct current (DC) is used in an electrocoagulation processes. In this case, an impermeable oxide layer may form on the cathode as well as corrosion formation on the anode due to oxidation. This prevents the effective current transfer between the anode and cathode, so the efficiency of electrocoagulation processes declines. These disadvantages of DC have been diminished by adopting alternating current (AC) in electrocoagulation processes. The main objective of this study is to investigate the effects of AC and DC on the removal of copper from water using magnesium alloy as anode and cathode.

Materials and methods

Magnesium alloy of size 2.0 dm² was used as anode and as cathode. To optimize the maximum removal efficiency, different parameters like effect of initial concentration, effect of temperature, pH, and effect of current density were studied. Copper adsorbed magnesium hydroxide coagulant was characterized by SEM, EDAX, XRD, and FTIR.

Results

The results showed that the optimum removal efficiency of copper is 97.8 and 97.2 % with an energy consumption of 0.634 and 0.996 kWh/m³ at a current density of 0.025 A/dm², pH of 7.0 for AC and DC, respectively. The adsorption of copper is preferably fitting the Langmuir adsorption isotherm for both AC and DC respectively. The adsorption process follows the second-order kinetics model with good correlation. Temperature studies showed that adsorption was endothermic and spontaneous in nature.

Conclusions

The magnesium hydroxide generated in the cell removes the copper present in the water, reducing the copper concentration to less than 1 mg/L, making it safe for drinking. The results of the scale-up study show that the process was technologically feasible.     

Fenton-like oxidation and mineralization of phenol using synthetic Fe(II)–Fe(III) green rusts

Background, aim, and scope  

In literature, the environmental applications of green rust (GR) have mainly been pointed out through the reduction of inorganic contaminants and the reductive dechlorination of chlorinated organics. However, reactions involving GR for the oxidation and mineralization of organic pollutants remain very scantly described. In this study, the ability of three synthetic Fe(II)–Fe(III) green rusts, GR(CO₃²⁻), GR(SO₄²⁻), and GR(Cl⁻), to promote Fenton-like reaction was examined by employing phenol as a model pollutant. Unlike the traditional Fenton’s reagent (dissolved Fe(II) + H₂O₂), where the pH values have to be lowered to less than 4, the proposed reaction can effectively oxidize the organic molecules at neutral pH and could avoid the initial acidification which may be costly and destructive for the in situ remediation of contaminated groundwater and soils. The green rust reactivity towards the oxidative transformation of phenol was thoroughly evaluated by performing a large kinetic study, chemical analyses, and spectroscopic investigations.     

Enantioselective toxicokinetics study of the bioaccumulation and elimination of α-hexachlorocyclohexane in loaches (Misgurnus anguillicaudatus) and its environmental implications

The enantioselective bioaccumulation and elimination of α-hexachlorocyclohexane (α-HCH) in loaches (Misgurnus anguillicaudatus) were studied for the first time. Valid chiral residue analysis methods for α-HCH enantiomers in water and loach samples were established using gas chromatography coupled with electron capture detector and a BGB-172 chiral column. A rapid accumulation process was found during the 39-d bioaccumulation experiment. The α-HCH in loaches reached its maximum on the fourth day, after which it fluctuated slightly, reflecting a balance between elimination and reuptake. The maximum bioaccumulation factor was 728 at the 10 μg L^?1 exposure level. The enantiomeric fraction (EF) values showed that the bioaccumulation was enantioselective with enantioenrichment of (+)-α-HCH in the loaches. The elimination experiment indicated that the degradation kinetics of α-HCH fitted a typical first-order kinetics model, and the half-life was about 5 d. Significant enantioselectivity was observed during the elimination process, with the EFs declining from higher than 0.5–0.39, suggesting (+)-α-HCH is preferentially biotransformed than (?)-α-HCH in loaches. The results reveal a high capacity for α-HCH bioconcentration by loaches and that biotransformation is the main route of decontamination.     

The ‘Storm of the Century’ (December 1999) and the accidental escape of Siberian sturgeons (Acipenser baerii) into the Gironde estuary (Southwest France)

GOAL, SCOPE AND BACKGROUND: The Gironde estuary is considered as a reference ecosystem with a large fish assemblage (75 species) and the presence of eleven diadromous species. However, geochemical studies and biomonitoring using oysters have shown high metal pollution levels. During the December 1999 hurricane, more than 5,000 young Siberian sturgeons (Acipenser baerii) accidentally escaped from a fish farm into the estuary, where this species had not been present until then. METHODS: In 2002/2003, thirteen sturgeons were collected from the estuary and twelve were obtained from the fish farm, from the same initial batch. Analysis of five metals (cadmium, zinc, copper, lead, mercury) measured in the gills, muscle, liver and kidneys, revealed significantly higher levels of cadmium, lead and mercury in the sturgeon collected from the estuary compared with those from the fish farm. RESULTS AND DISCUSSION: Metal analysis of the stomach contents of fish collected from the estuary and artificial food used in the fish farm indicated that dietary exposure might account for the differences observed. Nevertheless, metal concentrations in sturgeons that had spent about three years in the Gironde estuary may be considered low when compared with other species (mullets, eels) or with data in the literature regarding concentrations able to induce structural and functional perturbations in fish. As the introduced Siberian sturgeons live in the same place and feed on the same prey as the juveniles of the endangered A. sturio, our results indicate in the short-term that this strictly protected species does not appear to be much affected by the polymetallic pollution in the Gironde estuary. Marked differences in the concentrations of three metals (Cd, Pb, Hg) were established in four organs (gills, liver, skeletal muscle, kidneys) of Siberian sturgeons between specimens that had accidentally escaped into the Gironde estuary (France) during the December 1999 hurricane and were collected in March/June 2003 and specimens from the same initial batch at the fish farm. RECOMMENDATIONS AND PERSPECTIVES: Based on these results, a programme will be set up, with sampling campaigns carried out in the estuary every two years, with systematic monitoring of age in order to check the origin of individuals, in conjunction with sampling of sturgeon from the fish farm. This programme will complement other studies on several biological species representative of the main trophic levels in the estuary, especially the plankton component, benthic macroinvertebrates and oysters.     

Effects of Cutrine-Plus® algaecide and predators on wood frog (Lithobates sylvaticus) tadpole survival and growth

Copper contamination is increasing in many aquatic ecosystems. One mode by which copper can be introduced into aquatic ecosystems is as an algaecide, such as Cutrine-Plus®. Using a mesocosm experiment, we examined the effects of Cutrine-Plus® on wood frog (Lithobates sylvaticus) tadpoles. In addition, we examined how the presence of a nonnative predator the Western mosquitofish (Gambusia affinis) may interact with exposure to Cutrine-Plus®. Exposure to our low and high Cutrine-Plus® treatments had a strong negative effect on the wood frog tadpoles, and survivorship was greatly decreased in the low treatment, and no tadpoles survived in the high treatment. Additionally, the tadpoles that survived the low treatment were significantly smaller than those in the control treatment. Mosquitofish had no effect on the survivorship or growth of wood frog tadpoles, and mosquitofish presence did not have a significant interaction with the Cutrine-Plus® treatments. Cutrine-Plus® clearly had a negative effect on wood frog tadpoles at the concentrations used in our experiment, which were at and below the label-recommended dosages, suggesting that the use of Cutrine-Plus® in natural ponds may have negative consequences for wood frog populations and possibly other amphibians.     

Occurrence of organochlorine pesticides (OCPs) and their enantiomeric signatures, and concentrations of polybrominated diphenyl ethers (PBDEs) in the Adélie penguin food web, Antarctica

Concentrations and enantiomeric signatures of organochlorine pesticides were determined in Antarctic krill, emerald rockcod and Adélie penguin from the Ross Sea, Antarctica. HCB and DDTs were prevalent contaminants in penguin eggs. The highest concentrations of SigmaHCHs (1.35 +/- 0.72 ng/g) were found in the rockcod muscle, where gamma-HCH (1.23 +/- 0.67 ng/g) was the principal isomer. The ratio gamma-HCH/alpha-HCH was evaluated. Enantioselective gas chromatography was used for the evaluation of enantiomeric fractions (EFs) for alpha-HCH and oxychlordane. An increase of 14% in the (+)alpha-HCH enantiomer was found from krill through penguin, suggesting the enantioselective biotransformation increased proportionately with trophic level. Polybrominated diphenyl ethers (PBDEs) were measured and their concentrations were 5.6 +/- 1.12, 5.81 +/- 2.32, 4.57 +/- 0.17 and 3.06 +/- 3.27 ng/g lipids in krill, rockcod muscle, rockcod homogenate and penguin eggs, respectively. The detection of BDE28, BDE47, BDE99 and BDE100 in Antarctic organisms confirmed their global transport and distribution; the detection of lower brominated congeners suggested a potential long-range transport.     

The climatology of summertime O3 and SO2 (1977–1981)

The mean monthly distribution of the diurnal maximum O₃ and of the SO₂ in the eastern two-thirds of the U.S. was determined for the summer (July and August) of 1977–1981. Highest O₃ concentrations varied from 60 to 90 ppbv and covered an area of about 2 to 5 × 10⁶ km²; and that for SO₂ varied from values greater than 10 ppbv to values about 25 ppbv and covered an area of 0.3–1.3 × 10⁶ km². The geographical locations of the centers of high O₃ concentrations were related to the path of the anticyclones. The centers of high SO₂ concentration were affected by the path of anticyclones but to a lesser extent. The SO₂ distribution was controlled to a significant extent by the location of major SO₂ sources. The data suggested that highpressure systems that become stationary, weaken and dissipate in the eastern two-thirds of the U.S. have a profound effect on the O₃ and SO₂ distribution.     

Toxicological effects of active and inert ingredients of imazethapyr formulation Verosil® against Scenedesmus vacuolatus (Chlorophyta)

Environmental Science and Pollution Research - Imazethapyr, a selective systemic herbicide, is widely used in agriculture and it is frequently detected in water bodies close to application areas....     

Elemental and isotopic determination of lead (Pb) in particulate matter in the Brazilian city of Goiânia (GO) using ICP-MS technique

Environmental Science and Pollution Research - The toxic metal lead (Pb) can be harmful to human health in various manners, but is also considered as a distinguished tracer of environmental...     

Analyses of ozone in urban and rural sites in Málaga (Spain)

Ozone concentrations were measured at two (urban and a rural) sites near the city of Málaga (Spain). The aim of this study was to determine the daily, monthly and seasonal variation patterns of ozone concentrations at both sites and to study the possible regional influences. The daily variations mostly have the usual features with the afternoon maximum and the night minimum being more pronounced in the urban area. The average monthly concentrations throughout the year start to increase in March reaching their maximum values in July for the urban site. However, in the rural area, the monthly variations are smaller reaching their maximum value in June. The hourly evolution of the ozone concentrations in both sampling sites is well defined in spring and summer and not so well defined in autumn and winter. Taking into account the four seasons, the rural concentrations are higher than the urban ones. Summer is the season when there are similar concentrations at both sampling sites. Average hourly summer afternoon ozone for the hours 12:00-20:00 LST exceeded the 110 microg m(-3) European Union guidelines for human health for 8 h ozone exposure at the urban and rural sites.     

Spatial and temporal variability of ²¹⁰Po and ²¹⁰Pb in mussels (Mytilus galloprovincialis) at the Turkish coast of the Aegean Sea

In this study, the activity concentrations of ²¹⁰Po and ²¹⁰Pb were determined in mussel samples (Mytilus galloprovincialis) collected from the Turkish coast of the Aegean Sea. The samples were collected seasonally for a period of two years (2004-2006) at six coastal stations (Çanakkale, Dikili, Foça, Çe?me, Didim, Bodrum). Mussels were separated into several groups according to their size (1-4, 4-6, >6 cm). The results showed that ²¹⁰Po concentrations in mussels varied between 53 ± 4 and 1960 ± 60 Bq kg⁻¹ dw. The highest activity ²¹⁰Po concentrations were determined in winter samples of mussels with a shell length of 4-6 cm from Didim. In general, it was observed that the ²¹⁰Pb concentration levels in mussels were lower than ²¹⁰Po concentrations. The ²¹⁰Po/²¹⁰Pb activity concentration ratios exceeded unity for all mussel samples and averaged 26.0. The inter-site differences seen in ²¹⁰Po concentrations can be due to both the natural background levels of sites and industrial activities.     

Analysis of mobile source air toxics (MSATs)—Near-road VOC and carbonyl concentrations

Exposures to mobile source air toxics (MSATs) have been associated with numerous adverse health effects. While thousands of air toxic compounds are emitted from mobile sources, members of a subset of compounds are considered high priority due to their significant contribution to cancer and noncancer health risks and the contribution of mobile sources to total exposure as evaluated by the U.S. Environmental Protection Agency (EPA) National-Scale Air Toxics Assessments (NATA). These pollutants include benzene, 1,3-butadiene, ethylbenzene, acrolein, acetaldehyde, formaldehyde, naphthalene, polycyclic organic matter, and diesel particulate matter/organic gases. This study provided year-long trends of benzene, 1,3-butadiene, acrolein, acetaldehyde, and formaldehyde in Las Vegas, NV. Results indicated that MSAT concentrations often did not exhibit trends typical of other primary emitted pollutants in this study. Instead, other mobile sources beyond the highway of interest contributed to the measured values, including a major arterial road, a large commercial airport, and a nearby parking lot. The data were compared with relevant census-tract NATA estimates, with estimated ambient 1,3-butadiene concentrations similar to the measured values. Measured benzene values were much lower relative to the NATA total ambient benzene concentrations. Measured acrolein values were much higher relative to the NATA total acrolein concentrations. Measured acetaldehyde and formaldehyde values were also higher relative to the NATA total acetaldehyde and formaldehyde concentrations for all wind conditions and downwind conditions. Some possible explanations for these differences include nearby sources influencing the measured values; meteorological influences that may not be well captured by the NATA modeling regime; chemical reactivity of measured compounds; and additional explanatory variables may be needed for certain urban areas in order to accurately disaggregate anthropogenic air toxics emissions.

Implications: Comparison of air toxics concentrations measured at four long-term near-road sites in Las Vegas, NV, show generally good agreement with the EPA 2005 U.S. Environmental Protection Agency. 2005. National Air Toxics Assessments (NATA)(accessed December 7, 2012) http://www.epa.gov/ttn/atw/natamain/index.html (http://www.epa.gov/ttn/atw/natamain/index.html)  [Google Scholar] NATA total ambient concentrations. Measured concentrations did not compare as well with EPA 2005 U.S. Environmental Protection Agency. 2005. National Air Toxics Assessments (NATA)(accessed December 7, 2012) http://www.epa.gov/ttn/atw/natamain/index.html (http://www.epa.gov/ttn/atw/natamain/index.html)  [Google Scholar] NATA for the on-road mobile portion of the ambient concentrations. This highlights the complexity of air toxic emission sources and impacts in urban areas, especially around large highway facilities; NATA's inability to capture local-scale meteorology and fine-scale ambient gradients; and that additional explanatory variables may be needed for certain urban areas in order to accurately disaggregate anthropogenic air toxics emissions.     

The toxic effects of neem extract and azadirachtin on the brown planthopper, Nilaparvata lugens (Stål) (BPH) (Homoptera: Delphacidae)

Extracts of neem (Azadirachta indica A. Juss) are used in the developing world for many purposes including management of agricultural insect pests. The effects of different neem extracts (aqueous (NSKEaq), ethanol (NSKEeth) and hexane (NSKEhex)) on mortality, survival and weight of the brown planthopper, Nilaparvata lugens (St?l) (BPH) (Homoptera: Delphacidae) third and fourth nymphal instars were investigated. When fed rice plants treated with neem derivatives in bioassays, the survival of BPH nymphs is affected. Comparisons were made with the pure neem limonoid, azadirachtin (AZA) to ascertain its role as a compound responsible for these effects. AZA was most potent in all experiments and produced almost 100% nymphal mortality at 0.5 ppm and higher concentrations. When higher concentrations were applied, the effects appeared shortly after treatment and mortality was higher. Many insects died after remaining inactive for several days or during prolonged moulting. At lower concentrations, if moulting was achieved, disturbed growth and abnormalities were then likely to occur in the moulting process. Nymphs that were chronically exposed to neem extract showed a reduction in weight (45-60%). The results clearly indicate the simple NSKE (aqueous, ethanolic or both), containing low concentrations of AZA, can be used effectively to inhibit the growth and survival of BPH.     

Spatial distribution and mobility of organic carbon (POC and DOC) in a coastal Mediterranean environment (Saronikos Gulf, Greece) during 2007–2009 period

Particulate (POC) and dissolved organic carbon (DOC) is an important parameter for the pollution assessment of coastal marine systems, especially those affected by anthropogenic, domestic, and industrial activities. In the present paper, a similar marine system (Saronikos Gulf) located in the west-central Aegean Sea (eastern Mediterranean Sea) was examined, in terms of the temporal and spatial distribution of organic carbon (POC and DOC), with respect to marine sources and pathways. POC was maximum in winter in the Saronikos Gulf, due to the bloom of phytoplankton, whereas in the Elefsis Bay (located in the north side of the Saronikos Gulf) in summer, since phytoplankton grazes in the Bay in the end of summer (except for winter). Approximately 60 % of the bulk DOC of the water column was estimated as non-refractory (labile and semi-labile), due to the major anthropogenic, domestic, and industrial effects of the region and the shallow depths. The spatial distribution of POC and DOC mainly affects the northeastern section of the Gulf, since that region has been accepted major organic discharges for a long time period, in connection to the relatively long renewal times of its waters.     

Simultaneous measurements of ammonia and nitric acid in ambient air at Agra (27°10′N and 78°05′E) (India)

Simultaneous measurements of ammonia and nitric acid in ambient air were conducted at Dayalbagh, Agra using the mist chamber technique. The sampling site is located near a cattle shed. A total of 120 samples were collected during the period July–September and November–February (1997–1998). Sampling was performed during six different times a day. Gas-phase HNO₃ was estimated as NO₃⁻ using ion chromatographic technique while ammonia was determined colorimetrically as NH₄⁺ using indophenol blue method. The mean levels of NH₃ and HNO₃ for the entire data set were 16.3±2.8 and 1.6±1.4 ppbv, respectively. In the monsoon, mean values for NH₃ and HNO₃ averaged to 16.4±3.5 and 0.9±0.7 ppbv while the winter means were 11.8±4.4 and 2.1±1.2 ppbv, respectively. Concentration of both the species (NH₃ and HNO₃) did not show any significant diurnal behaviour in both the seasons. However, concentration of both NH₃ and HNO₃ were lower at dawn than the previous night's value. This has been ascribed to their removal through dew. Concentrations of HNO₃ are observed to increase during the daytime, consistent with its formation by photochemical reactions. Nitric acid and ammonia concentrations show a significant seasonal variation. Levels of HNO₃ are higher in winter but lower in monsoon, while ammonia shows a reverse trend with higher monsoon and lower winter values. Observed trends in nitric acid and ammonia concentration are due to seasonal variation in emission sources, chemistry and meteorology. Gaseous ammonia and nitric acid are in equilibrium with NH₄NO₃ (solid or aqueous) in the atmosphere. The existence of this equilibrium was examined from simultaneous measurements of NH₃ and HNO₃ in the ambient air. It is found that for the monsoon data, measured concentrations are qualitatively below the predicted equilibrium value, while in the winter, concentration product ([NH₃] [HNO₃]) lies consistently above the predicted values. These deviations may be explained due to local sources of both [NH₃] and [HNO₃], presence of coarse nitrate particles and low-temperature and high-humidity conditions.