Seasonal variations of dustfall fluxes and biochemical parameters in the foliage of selected indoor plants in Delhi, India.

This study reports the seasonal variations in dry deposition of coarse and fine particles on the foliar surfaces of common indoor plants viz. Ficus elastica, Ficus lyrata, and Schefflera arboricola along with their biochemical changes in the urban households of metropolitan Delhi. The dustfall fluxes were significantly higher at the industrial site as compared to residential site and temporal variations indicated higher dustfall fluxes during the winter months as compared to other seasons. Seasonal concentrations of chlorophylls, pH, and soluble sugars were higher during monsoon season for the indoor plants whereas ascorbic acid content was higher in the winter season indicating more stress. The results of correlation plots revealed that the variations observed in the biochemical traits were interlinked with the changes in dustfall fluxes during different seasons, thereby reflecting the changes in air pollution stress faced by plant foliage. The air pollution tolerance index and anticipated performance index were evaluated to understand the overall tolerance of indoor plants toward air pollution which can be utilized in phytoremediation techniques. It was concluded that among the studied indoor plants, Ficus elastica and Ficus lyrata are better plant species than Schefflera arboricola for improving indoor air quality.

The novelty of this work lies in studying the spatial and temporal variations in the deposition of indoor dust on foliar surfaces of plants in the households of a highly polluted metropolitan. Based on the biochemical parameters, the air pollution tolerance index (APTI) and anticipated performance index (API) have been calculated for the first time for Ficus elastica, Ficus lyrata, and Schefflera arboricola. The study strengthens the existing knowledge regarding the role of leaves as a platform to capture dust particles and role of indoor plants in improving air quality. The outcomes of this study can be applied in modern day concepts for urban areas such as nature-based solutions for air pollution mitigation, vertical greenery systems (VGS), green roofs, and outdoor green walls.

Gaseous and particulate reactive nitrogen species in the indoor air of selected households in New Delhi.

The present study reports the indoor abundance of inorganic trace gases (NH3, NO2 and SO2) and their corresponding particulates (NH4+, NO3- and SO42-) along with other major ionic species present in the aerosol form (Cl-, F-, Na+, K+, Ca2+ and Mg2+), in the urban households of megacity Delhi (India). Two different households (DH site and MH site) were selected in the city based on the variation in the land use patterns of the locations in which they were situated. Trace gases followed the order NH3 > SO2 > NO2 at both the sites with NH3 contributing about 90% and 85% to the total Nr species at DH and MH sites, respectively. NH3 showed maximum indoor concentrations during monsoon season whereas NO2 and SO2 were higher during winter season. The gas to particle conversion of the inorganic trace gases was studied by calculating their oxidation ratios which followed the order SOR > NOR > NHR, indicating that SO2 showed more oxidative conversion to SO42- as compared to NO2 and NH3 in the indoor setup. The chemical composition of the particulates revealed that Ca2+ and SO42- were the most abundant cation and anion, respectively, among the measured ionic species at both sites and the concentrations of all the major ions were higher for the industrial MH site as compared to the residential DH site. Source apportionment using principal component analysis and mass ratios showed that indoor activities such as cooking, cleaning along with others such as biomass burning and dust resuspension were responsible for the indoor composition of particulates at DH site whereas outdoor influences such as coal burning and industrial emissions from local sources were prominent at MH site due to its industrialized surroundings. For naturally ventilated households (such as the present study), it was observed that the emissions generated indoors as well as the characteristic outdoor influences seem to influence the overall indoor air composition and quality.

Industrial dust sulphate and its effects on biochemical and morphological characteristics of Morus (Morus alba) plant in NCR Delhi.

Abundance of CaCO3 rich soil dust is a typical feature of atmospheric environment in the Indian region. During prevailing dry weather conditions, dustfall is deposited onto the foliar surfaces of plant affecting their morphology, stomata and the levels of biochemical constituents. This study reports the chemical characteristics of dustfall, its effect on foliar morphology and biochemical constituents of a medicinal plant (Morus alba) at two sites which are differentiated on the basis of landuse pattern, viz., (i) residential, Jawaharlal Nehru University (JNU), and (ii) industrial, Sahibabad (SB), located in the National Capital Region (NCR) of Delhi. Dustfall was characterized for major anions (F(-), Cl(-), NO3 (-) and SO4 (--)) and cations (Na(+), NH4 (+), K(+), Mg(++) and Ca(++)). Biochemical parameters such as chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, proline and ascorbic acid were determined in foliar samples. The results showed that the dustfall fluxes of all the major ions were found to be higher at the industrial site (SB) as compared to the residential site (JNU). Foliar analysis revealed that the levels of biochemical parameters were more affected at SB site due to higher levels of dust SO4 (--) contributed by various anthropogenic sources resulting in more stressful conditions affecting the biochemistry of the plant. The possible entry pathways for dust SO4 (--) into foliar cells are also discussed in the paper. It was noticed that the deposition of urban dust was responsible for the damage of trichome, epidermis, cuticle and stomatal guard cells significantly affecting foliar morphology. SB exhibited more damage to these morphological parts suggesting that industrial dust is harmful to the plants.

Spatial and temporal patterns of air pollutants in rural and urban areas of India.

In this study, we analysed spatial and temporal patterns of Suspended Particulate Matter (SPM) concentrations across India. We have also assessed MODIS-derived aerosol optical depth (AOD) variations to characterize the air quality and relate it to SPM, NO2 and SO2 in different areas. In addition, the pollutant concentrations have been mapped using geospatial techniques. The results indicated significant differences in air pollutant levels across rural and urban areas. In general, districts of central and northern India had relatively higher SPM concentrations compared to southern India. Out of the top ten SPM polluted districts in India, nine were located in the state of Uttar Pradesh (UP). We observed significant correlations between the SPM and AOD at different sites. Although spatial and temporal patterns of NO2 and SO2 matched AOD patterns, the correlation strength (r2) varied based on location. The causes and implications of these findings are presented.

Precipitation and aerosol studies in India.

In India, rain water and atmospheric aerosols are observed to be alkaline in nature due to the influence of soil-derived particles which are rich in components like Ca and Mg. These components increase the neutralization potential of rain water and have a greater influence at rural site compared to urban site. However, if there are continuous rains, the concentration of crustal components becomes lower resulting in lower pH of rain water. Unlike the characteristics of rain water on continent, the pH of rain water has been observed to be acidic in all the events over the Indian Ocean during Pre-campaigns of Indian Ocean Experiment (INDOEX). The possible reason for acidic rains over Indian Ocean could be the anthropogenic contribution from continent transported by NE winds coming towards the ocean during this period.

Identification of the nature and source of atmospheric aerosols near the Taj Mahal (India).

The chemical composition of aerosol samples collected at Agra near the Taj Mahal during April 1991-June 1992 was identified by wet chemical analysis. The average concentration of suspended particulate matter (SPM) was 368.5 µg m(-3), ranging between 83 and 1305 µg m(-3), depending upon the season. Elevated levels of Na, SO4, Mg, NO3 and Cl compared to levels reported worldwide were attributed to the suspension of soil particles, as well as industrial emissions. Geometric mean enrichment factors of elements indicated two groups; one having enrichment factors less than 7 which were comprised of Na, K, Ca, Mg, Fe, Al, Mn and Si (crustal) and the other having enrichment factors greater than 13 and which were comprised of Ni, Cu, Zn, Pb, and Cd (non-crustal). Principal component analysis revealed the association of the first principal component with soil-derived elements while the second, third and fourth principal components were associated with industrial processes, wood combustion and brick kilns respectively. The study indicates that near the Taj Mahal the dominance of natural sources may enhance the degree of deterioration of the marble surface if micro-climatological conditions favour its wetting.

Factors affecting alkaline nature of rain water in Agra (India).

Rain water was collected and analysed from a reference site, Dayalbagh and Taj Ganj, near the Taj Mahal in Agra. The ionic components Ca, Mg, Na, K, NH(4), Pb, Fe, Zn, SO(4), HCO(3), Cl and F were analysed along with pH, alkalinity and conductance. The average pH of rain water at both sites is 7.05. There is a dominance of alkaline components, particularly Ca. The rain water chemistry shows the importance of calcareous soil-derived materials in controlling the pH of rain water.