S. S. Srivastava

Atmospheric formic and acetic acids: An overview

Interest in the role of organic acids as chemical constituents in troposphere has been growing rapidly over the past couple of decades. In addition to their presence in the atmosphere in a variety of phases, organic acids are important constituents of the global troposphere and contribute a large fraction (∼25%) to the nonmethane hydrocarbon atmospheric mixture. They contribute significantly to the acidity of precipitation and cloud water, especially in remote regions. In this review, we consider the information presently available on concentration distribution of formic and acetic acids in multiple phases and their sources in different geographical locations, i.e., midlatitude continental, tropical continental and marine sites. Photochemical reactions (i.e., ozone-olefin reaction, isoprene oxidation, gas phase reaction of formaldehyde with HO2, and aqueous phase oxidation of formaldehyde) are important sources of these acids. In midlatitude continental regions, possible sources of formic and acetic acids, in addition to photochemical reactive vehicular emission, are direct emission from vegetation and biomass burning. In tropical continental sites, direct emission from vehicles, ants, soil, vegetation, and biomass burning are the important source of these species. The probable sources at marine locations are photochemical reactions, biogenic emissions, and long-range transport from continental sites.

Chemical Composition and Association of Size-Differentiated Aerosols at a Suburban Site in a Semi-Arid Tract of India

Size-differentiated concentrations of SPM, F, Cl, NO3, SO4, Na, K, Ca, Mg and NH4 in atmospheric aerosols were measured in a suburban area of Agra city during December 1992 to March 1993. Except for NH4, Cl and Na, all components were found to have a bimodal distribution. The fine fraction was dominated by NH4, K, NO3 and SO4, while Na, Ca, Mg, F and Cl contributed to the coarse fraction. Fifty-eight percent of SO4 and 67% of NO3 were found in the fine mode and the coarse mode comprised 42 and 33% of SO4 and NO3, respectively. SO4 was found to have a peak above the submicron range at 1.1 µm which has been attributed to secondary sulphate formation by heterogeneous oxidation of SO2 on alkaline particles of Ca and Mg. The total aerosol was basic in nature and dominated by the soil-derived acid neutralising components (Ca, Mg and Na).

HCHO, HCOOH and CH3COOH in air and rain water at a rural tropical site in North Central India

HCHO, HCOOH and CH3COOH were measured in vapour phase and rain water during monsoon period at Gopalpura, Agra a rural site of north central semi-arid tract of India. Mean concentrations of formaldehyde, formic and acetic acids were 1.4, 1.7 and 1.6 ppbv in the vapour phase and were 4.4, 5.4 and 4.8 μmol l−1 (volume weighted) in rain water, respectively. Due to cloud cover and rain which occurs intermittently in monsoon these species did not show typical diurnal pattern as reported by others. In the gas phase a good correlation of formic acid with acetic acid (r = 0.78) and poor correlation with formaldehyde (r = 0.19) suggested that formic and acetic acids may also have significant contributions from other than photochemical sources such as biogenic sources. The strong correlation between formate and acetate (r = 0.96) and formate and formaldehyde (r = 0.95) in rain water suggests that their sources are common, if not identical. Regression analysis between concentration vs precipitation volume and deposition amount vs precipitation volume of the three species suggested that concentration of these species are almost independent of rain volume and controlled by a continuous supply of these species by slowly scavenged material or oxidation of aldehyde to organic acid. HCOO−/HCHO ratio (1.4) also suggested that aqueous-phase oxidation of formaldehyde is a major source of formic acid in rain water.

Chromium mobilization and plant availability — the impact of organic complexing ligands

Pot experiments were conducted to investigate the effect of various organic acids (carboxylic and amino acids) on the uptake and translocation of root-absorbed trivalent chromium by tomato ( Lycopersicum esculentum) plants grown in sand and soil culture. Statistically significant increases in chromium accumulation from Cr(III) treated plants in the presence of increasing concentrations of organic acid suggest the existence of Cr(III) — organic acid interactions in the soil-plant system. However, the amino acids have been less effective in the mobilization of chromium compared to carboxylic acids. The results are discussed on the basis of the potential of organic acids to form complexes with Cr(III).

Studies on uptake of trivalent and hexavalent chromium by maize (Zea mays)

Pot culture experiments were carried out to study the uptake and translocation of chromium from irrigation water when supplied in its trivalent and hexavalent states to maize plants grown in soil and sand culture. The uptake of chromium was observed to increase with increase in the concentration for both oxidation states of chromium. For the root, the observed order of uptake was CrIII sand > CrVI sand > CrIII soil > CrVI soil, whereas in the lower shoot, upper shoot and fruit the order was CrVI sand > CrVI soil > CrIII sand > CrIII soil. Significantly high uptake of chromium by roots in the sand culture (CrIII treatment) is attributed to the effect of root exudates and degradation products on the mobilization of CrIII. In aerial parts of the plants a higher uptake was observed when the initial supply was CrVI. The trends observed are explained on the basis of the redox behaviour of chromium.

Study of mercury-selenium (HgSe) interactions and their impact on Hg uptake by the radish (Raphanus sativus) plant

Pot culture experiments were conducted to study the effects of selenite and selenate treatment (0.5-6.0 microg/ml) on the uptake and translocation of root-absorbed mercury (Hg) in radish plants irrigated with 2 and 5 microg/ml Hg in sand and soil culture. Statistically significant reductions in mercury uptake with increasing concentrations of selenium (Se) were observed. Both forms of selenium (selenite and selenate) were equally effective in reducing the mercury burden of the plant. The observed reduction in plant uptake of mercury is explained by the formation of an HgSe insoluble complex in the soil-root environment. No significant difference (P > 0.05) in dry matter yields with the various selenium treatments was found, suggesting that no selenium toxicity or salt injury occurred in the plants.

Measurements of major ion concentration in settled coarse particles and aerosols at a semiarid rural site in India

Deposition rates and deposition velocities of water-soluble ions (F, Cl, NO3, SO4, NH4, Ca, Mg, Na and K) were measured at a rural site (Gopalpura, Agra). Dry deposition samples were collected throughout the year from December 1995 to August 1997, while the aerosol samples were collected only during the winter season of 1996. Surrogate technique was used to collect the dry deposition samples, while aerosol samples were collected on PTFE membrane filter. Deposition velocities (Vd) of SO4 and NO3 are < or = 0.01 m s(-1) while Ca, Mg, Na, K, NH4, F and Cl exhibit greater than 0.01 m s(-1) Equivalent concentration ratios of K/Na, Ca/Na and Mg/Na conform with the corresponding ratios of local soil, indicating the dominant contribution of local sources. Deposition rates are maximum in winter, followed by summer and monsoon. No significant differences are found in dry deposition rates of all ions or in atmospheric concentrations of soil-derived elements with respect to wind direction. However, in aerosols, concentrations of F, Cl, NO3 and SO4 are higher with winds from southwesterly and westerly directions corresponding to pollution sources located in these directions. Deposition data have been used to calculate the critical load of S and N for soil with respect to Triticum vulgaris. The critical load of actual acidity was found to be 622.4 eq ha(-1) year(-1) within the range of 500-1,000 eq ha(-1) year(-1) as assessed by the RAINS-Asia model for this region. The present load of S and N (77.4 and 86.4 eq ha(-1) year(-1)) was much lower than the critical load of S and N (622.4 and 2,000 eq ha(-1) year(-1)), indicating that at present there is no harmful effect on ecosystem structure and function.

Multiphase measurement of atmospheric ammonia

Abstract Measurement of ammonia in vapour phase, particulate and rain was made at a suburban site of India. Vapour phase concentrations varied between 0.97 and 25.5 μg m−3 (57.1–1500.0 nmol m−3) and diurnal variation study showed high concentration of NH3 during night time and minimum at 0600 h (early morning). Particulate phase NH4 values ranged between 1.2 and 5.3 μg m−3 (66.7–294.4 nmol m−3). Dry deposition flux was determined from model calculations. Day time NH3 flux was found to be 8.4±4.0 mg m−2 d−1 and that of night 2.2±1.2 mg m−2 d−1. With respect to particulate deposition flux was found 0.2±0.1 mg m−2 d−1 while in precipitation values of NH4 ranged between 0.7 and 74.4 μeq l−1. Regression analysis of ammonium concentration with rain volume and deposition indicates that NH3 concentration is being controlled by both gas and particulate ammonium. Annual inputs for wet and dry deposition were found to be 0.34±0.3 and 3.9±1.9 g m−2 y−1.

A study on the uptake of trivalent and hexavalent chromium by paddy (Oryza sativa) : possible chemical modifications in rhizosphere

The uptake and translocation of chromium by paddy (Oryza sativa L. Arbario) was studied using radiotracers. Chromium was supplied as Cr III and Cr VI through irrigation water and plants were grown in sand and soil culture. The uptake of chromium for both the oxidation states and culture types was found to increase more or less linearly with the increase in chromium concentration though with different slopes. The rate of increase of the uptake when compared to the increase in feed concentration indicates that the uptake by roots is mediated possibly through a passive mechanism. For a given concentration of feed, values of chromium in μgg−1 dry matter in shoot and grain did not vary significantly either for different oxidation states of feed chromium or culture type. The order of uptake for paddy shows a considerably different pattern when compared to onion, maize and groundnut. This has been qualitatively explained on the basis of the different chemistry of chromium in the rhizosphere of paddy. The amount of chromium translocated to grain was also considerably less compared to the other three crops.

Dry deposition of sulphate and nitrate to polypropylene surfaces in a semi-arid area of India

Abstract Dry deposition rates of the major ionic species Cl − , NO 3 − , SO 4 2− , Na + , K + , Ca 2+ and Mg 2+ were estimated by the surrogate collection technique using polypropylene surfaces. The dry deposition rates of the soil derived cations Ca 2+ , Na + , K + and Mg 2+ were of the order of 0.4–6.1 mg m −2 d −1 . The dry deposition rates of the acidic ions NO 3 − and SO 4 2− were of similar magnitude, suggesting that they are also soil derived or associated with the soil elements. On a seasonal basis, deposition rates were maximum during the winter followed by summer and minimum during the monsoon.