P. Khare

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.

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.

Measurements of formic and acetic acid levels in the vapour phase at Dayalbagh, Agra, India

Abstract Acetic and formic acid concentrations were determined in the vapour phase at ground level at Dayalbagh, Agra, during the winter and summer of 1992–1993. Ion chromatography was used to measure the species. Yearly means were 1.7±1.6 ppbv for acetic acid and 1.3±1.4 ppbv for formic acid ( N = 137). Average winter mixing ratios ( N = 60) for acetic acid and formic acid were 1.8±1.6 and 1.4±1.4 ppbv, respectively, and the corresponding summer levels ( N = 77) were 1.3±1.2 and 1.1±1.2 ppbv but seasonal variation was not statistically significant. These concentrations are within the range reported at other sites worldwide. The F A (formate-to-acetate) ratio showed a diurnal variation with higher averages in the day (1.2) than at night (0.45). With respect to wind direction, the W sector appears to be the cleanest and is associated with the lowest mean concentrations of acetic and formic acids; local sources as well as the ones on a larger scale appear to contribute to the levels recorded in this study.

Rainwater Composition at a Regional Representative Site of a Semi-Arid Region of India

Rainwater samples (N = 51) were collected at Rampur, an areafree from anthropogenic activity during the monsoon of 1997 and1998. The concentration of ions follows a general pattern as Ca> NH4 > Mg > SO4 > Cl > F >Na > NO3 > K > HCOO >CH3 COO. The pH of precipitation ranges between 5.9 and 7.4. The levels of Ca and Mg at this site are higher than otherremote sites, probably dominated by particles of soil origin.Good correlation between Ca, NO3, SO4, HCOO and CH3COO indicate that a fraction of NO3, SO4, HCOOand CH3COO may be derived from soil or associated with Ca and Mg after neutralization. The order of neutralization factorCa (2.19) > NH4 (1.26) = Mg (1.26) indicates that majorneutralization occurred by Ca. Factor analysis suggested thatCa, Mg, Na, K, NO3, SO4, HCOO and CH3COO arecontributed by soil. NH3 is known to exist as(NH4)2SO4, NH4NO3 and NH4Cl. Theymay be formed in the atmospheric water droplets by scavenging ofaerosols and reaction of gaseous species.

Formate and acetate levels compared in monsoon and winter rainwater at Dayalbagh, Agra (India)

A total of 59 rainwater samples were collected during the winter and monsoon (1991–92) at Dayalbagh, Agra. This site is relatively free from the influence of anthropogenic emissions and the volume-weighted average concentrations (VWA) of formate in the winter and monsoon were 22.5±6, 16.1±3 while acetate VWAs were 17.1±5 and 13.8±3 μmol l-1, respectively. Although the VWAs varied between seasons, it was not statistically different. Total deposition (in mmol m-2) varied between season (winter formate, 1.4; acetate, 1.1; monsoon formate, 7.4; acetate, 6.4). A difference in VWA values may have occurred as a result of the dilution factor; the total rain depth from collected samples in the monsoon was 46 cm while that in winter was 6.3 cm. Sources at this site may be anthropogenic and natural; scavenging from the vapour phase, washout of soil particles and emissions from vegetative sources are probably important sources for formate and acetate.

Formate and acetate in particulate matter and dust fall at Dayalbagh, Agra (India)

Formate and acetate were estimated in particulate matter and dust fall at Dayalbagh. The mean concentration of formate and acetate in particulate matter was 290±-205 and 320±-90 ng m−3 in the winter and 240±-160 and 440±-100 ng m−3 in the summer. The percent of formic acid present in the particulate phase was 29% in the winter and 25% during the summer while the same values for acetic acid were 29% and 43%, respectively. Higher percentages of both acids in particulate phase compared to those observed at other sites were attributed to the basic nature of aerosol at this site. In dust fall, the fluxes of formate in the winter and summer were 132±-114 and 155±-55 μg m−2 day−1, respectively while corresponding acetate fluxes were 177±-166 and 80±-54 μg m−2 day−1. Higher fluxes at this site is contributed by higher atmospheric loading of particulate matter, dominated by the soil-derived elements. The estimated deposition velocities of particulate formate were 0.5±-0.6 cm s` in winter and 0.3±-0.6 cm s−1 in summer while vd′s for particulate acetate were 1.0±0.9 cm s−1 in winter and 0.5±-0.6 cm s−1 in summer.

Surface measurements of formaldehyde and formic and acetic acids at a subtropical semiarid site in india

Vapor phase formaldehyde, formic acid, and acetic acid (HCHO, HCOOH, and CH3COOH) were measured at Dayalbagh, a suburban site in Agra. The average mixing ratios of formaldehyde, formic acid and acetic acid for the entire data set (N=60) were 0.8±0.5 parts per billion by volume (ppbv), 1.4±0.8 ppbv, and 0.9±0.3 ppbv, respectively. Maximum levels of HCHO were observed between 1500 and 1900 hours (LT) possibly because of an increase in in situ formation up to 1600 hours. The extension of maximum concentration up to 1900 hours was probably due to low rates of HCHO removal as a result of diminished insolation and a decrease in OH concentration. Formic and acetic acids showed elevated levels between 1000 and 1600 hours, probably due to active photochemistry and direct emissions. HCOOH and CH3COOH correlated significantly with each other but not with HCHO. This finding suggested the origin of both the acids from the same sources, while HCHO had different pathways. Rates of direct emission, in situ formation, and removal by dry deposition were estimated for both acids. In situ reaction produced more formic acid than acetic acid. Production of acetic acid was seen to be dominated by direct emissions. The production estimates exceed removal by a factor of ≈2.5; these fall within the uncertainty limits.

Variation in Ionic Composition of Precipitation Collected by Sequential Sampling

Thirty-four rain water samples of equal volume (60 mL corresponding to 3.6 mm rain) were collected sequentially from five showers during the monsoon of 1994, at Agra situated in a semi arid zone in India. Conductivity, pH, F−, Cl−, NO3 −, SO4 2−, Na+, K+, NH4 +, Ca2+, and Mg2+ were determined in the samples. The concentration of all the anions and cations decreased progressively till the end of the event. Fifty percent of the total concentration of the ionic components is removed in the first two samples of events. On the basis of correlation coefficients between the first samples of each event, Ca2+ appeared to be the dominant neutraliser of H+ acidity (Ca2+ and NO3 −=0.80; Ca2+ and SO4 2− = 0.93), while in the second sample ammonium emerged as another important acid-neutralising species (NO3 − and NH4 + = 0.89; SO4 2− and NH4 + = 0.61). In subsequent samples, in addition to Ca2+ and NH4 +, other cations (Mg2+, K+, Na+) were also found to act as acid neutralisers (NO3 − and NH4 + = 0.83; Na+ and NO3 − = ...

Deriving critical loads for the Agra region in India

Abstract A steady state mass balance (SMB) method was used to calculate the critical load of S and N for soil. The present load of sulphur (160.6 Eq ha −1 year −1 ), nitrogen (49.6 Eq ha −1 year −1 ) and ammonium (172.4 Eq ha −1 year −1 ) were calculated from wet and dry depositions collected from the Agra region. The values of the critical load of S and N for soil with respect to Cenchrus ciliaris (Anjan grass) were 309.2 and 381.8 Eq ha −1 year −1 , respectively. The present loads are lower than the critical loads in this region. The critical loads calculated by the SMB method from the experimental data are in agreement with the results obtained from the RAINS-Asia model for this region.