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A detailed time-resolved chemical characterization of ambient nonrefractory submicron aerosols (NR-PM1) was conducted for the first time in India. The measurements were performed during the winter (November 2011 to January 2012) in a heavily polluted city of Kanpur, which is situated in the Indo-Gangetic Plain. Real-time measurements provided new insights into the sources and evolution of organic aerosols (OA) that could not be obtained using previously deployed filter-based measurements at this site. The average NR-PM1 loadingwas very high (&gt;100 µg/m3) throughout the study, with OA contributing approximately 70% of the total aerosol mass. Source apportionment of the OA using positive matrix factorization revealed large contributions from fresh and aged biomass burning OA throughout the entire study period. A back trajectory analysis showed that the polluted air masses were affected by local sources and distant source regions where the burning of paddy residues occurs annually during winter. Several fog episodes were encountered during the study, and the OA composition varied between foggy and nonfoggy periods, with higher oxygen to carbon (O/C) ratios during the foggy periods. The evolution of OA and their elemental ratios (O:C and H:C) were investigated for the possible effects of fog processing. © 2015. American Geophysical Union. All Rights Reserved.

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Department of Civil & Infrastructure Engineering

Fulltext

Journal of Geophysical Research

Real-time measurements of ambient aerosols in a polluted Indian city: Sources, characteristics, and processing of organic aerosols during foggy and nonfoggy periods

Atmospheric aerosols are key elements in cloud microphysics, the hydrological cycle and climate by serving as cloud condensation nuclei (CCN). The present work analyzes simultaneous measurements of number concentration of CCN (NCCN) and condensation nuclei (NCN) obtained at Nainital, in the Gangetic-Himalayan (GH) region, during the frameworks of Ganges Valley Aerosol Experiment (GVAX), June 2011 to March 2012. The NCCN, NCN and activation (AR=NCCN/NCN) at 0.31-0.33% S (supersaturation ratio), exhibit significant daily, monthly and seasonal variations within a range of 684-2065cm-3 for NCCN, 1606-4124cm-3 for NCN, and 0.38-0.60 for AR, suggesting large inhomogeneity in aerosol properties, types and sources, which control the degree of aerosol potential activation. Thus, transported aerosols from the Ganges valley and abroad, the boundary-layer dynamics and atmospheric modification processes play an important role in aerosol-cloud interactions over the GH region. The NCN and NCCN show monthly-dependent diurnal variations with afternoon maxima due to transported aerosols from the Ganges valley up to the Himalayan foothills, while the AR is lower during these hours implying lower hygroscopicities or smaller sizes of the transported aerosols. The dependence of NCCN on S is highest during Dec-Mar and lowest during monsoon (Jun-Sep), suggesting different aerosol chemical composition. Comparison between Nainital and Kanpur shows that NCN and NCCN are much lower at Nainital, while the similarity in AR suggests aerosols of similar type, source and chemical composition uplifted from the Ganges valley to the Himalayan foothills. © 2014 Elsevier B.V.

Atmospheric Research

Seasonal inhomogeneity in cloud precursors over Gangetic Himalayan region during GVAX campaign

This study presents a detailed cloud condensation nuclei (CCN) closure study that investigates the effects of chemical composition (bulk and size resolved) and mixing state (internal and external) on CCN activity of aerosols. Measurements of the chemical composition, aerosol size distribution, total number concentration, and CCN concentration at supersaturation (SS = 0.2-1.0%) were performed during the winter season in Kanpur, India. Among the two cases considered here, better closure results are obtained for case 1 (low total aerosol loading, 49.54 ± 26.42 µg m-3, and high O:C ratio, 0.61 ± 0.07) compared to case 2 (high total aerosol loading, 101.05 ± 18.73 µg m-3, and low O:C ratio, 0.42 ± 0.06), with a maximum reduction of 3-81% in CCN overprediction for all depleted SS values (0.18-0.60%). Including the assumption that less volatile oxidized organic aerosols represent the soluble organic fraction reduced the overprediction to at most 40% and 129% in the internal and external mixing scenarios, respectively. At higher depleted SS values (0.34-0.60%), size-resolved chemical composition with an internal mixing state performed well in CCN closure among all organic solubility scenarios. However, at a lower depleted SS value (0.18%), closure is found to be more sensitive to both the chemical composition and mixing state of aerosols. At higher SS values, information on the solubility of organics and size-resolved chemical composition is required for accurate CCN predictions, whereas at lower SS values, information on the mixing state in addition to the solubility of organics and size-resolved chemical composition is required. Overall, κtotal values are observed to be independent of the O:C ratio [κtotal = (0.36 ± 0.01) × O:C - (0.03 ± 0.01)] in the range of 0.2&lt;O:C&lt;0.81, which indicates that the variation in the chemical composition of aerosols is not well represented by the changes in the O:C ratio alone. © 2014. American Geophysical Union. All Rights Reserved.

CCN closure study: Effects of aerosol chemical composition andmixing state

We present long-term measurements of sub-micron particle number size distributions (PNSDs) conducted at an urban location, Kanpur, in India, from September 2007 to July 2011. The mean Aitken mode (NAIT), accumulation mode (NACCU), the total particle (NTOT), and black carbon (BC) mass concentrations were 12.4×103cm-3, 18.9×103cm-3, 31.9×103cm-3, and 7.96μgm-3, respectively, within the observed range at other urban locations worldwide, but much higher than those reported at urban sites in the developed nations. The total particle volume concentration appears to be dominated mainly by the accumulation mode particles, except during the monsoon months, perhaps due to efficient wet deposition of accumulation mode particles by precipitation. At Kanpur, the diurnal variation of particle number concentrations was very distinct, with highest during morning and late evening hours, and lowest during the afternoon hours. This behavior could be attributed to the large primary emissions of aerosol particles and temporal evolution of the planetary boundary layer. A distinct seasonal variation in the total particle number and BC mass concentrations was observed, with the maximum in winter and minimum during the rainy season, however, the Aitken mode particles did not show a clear seasonal fluctuation. The ratio of Aitken to accumulation mode particles, NAIT/NACCU, was varied from 0.1 to 14.2, with maximum during April to September months, probably suggesting the importance of new particle formation processes and subsequent particle growth. This finding suggests that dedicated long-term measurements of PNSDs (from a few nanometer to one micron) are required to systematically characterize new particle formation over the Indian subcontinent that has been largely unstudied so far. Contrarily, the low NAIT/NACCU during post-monsoon and winter indicated the dominance of biomass/biofuel burning aerosol emissions at this site. © 2014 Elsevier B.V.

Sub-micron particle number size distributions characteristics at an urban location, Kanpur, in the Indo-Gangetic Plain

We present properties of size-resolved cloud condensation nuclei (CCN) over the central Indo-Gangetic Basin (IGB) station, Kanpur, India. The measurements were done during three different seasons: spring, summer and monsoon in 2012. Size-resolved CCN efficiency spectra (20-280nm), measured at 0.2-1% supersaturation (SS), resulted in an average activation diameter (Da) of 148-45nm. The activation diameter was found to be maximum in spring followed by monsoon and summer at all SS except at SS=1%. The size-averaged hygroscopicity (κ) of CCN-active particles for all SS was found to be 0.11±0.03, 0.24±0.13 and 0.14±0.06 in spring, summer, and monsoon, respectively. κ increased with increasing particle diameter, suggesting change in chemical composition with size which further leads to change in CCN activity. In comparison to summer and monsoon, despite the presence of lower κ in spring, the higher activation fraction in Aitken mode is observed due to the shift of CN size distribution towards larger diameter. κ is observed to be lower in first half of the day (0900-1400h) for SS=0.2-0.5% due to relatively less photochemical activity compared to second half of the day. Size-and-time averaged κ value over all three seasons (0.16±0.08) suggests dominance of organic species, as reported in previous studies. © 2013 Elsevier Ltd.

Atmospheric Environment

Inter-seasonal variability in size-resolved CCN properties at Kanpur, India

The aim of this study conducted at Kanpur (26.51°N, 80.23°E), India, was to quantify chemical properties of dust and the intensity of mixing, due to its interaction with various emissions from anthropogenic activities, during its long range transport. Aerosol mass was collected at Indian Institute of Technology, Kanpur (IIT-K) located in the Indo-Gangetic Plain from April-July 2011, a period marked by intense dust storms and onset of monsoon. The sampling days were classified as Dust, Polluted Dust1 (PD1), Polluted Dust2 (PD2) and Continental days. PM10 (coarse mode) and PM2.5 (fine mode) collected on filter substrates were analysed for chemical composition. Elemental concentrations were measured using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). The results show that crustal elements like Ca, Fe, K, Na and Mg were dominant in coarse mode during dusty days, whereas, elements of anthropogenic origin like Cu, Ni, Se and V were mostly concentrated in fine mode during PD1 as well as PD2.Very low elemental concentrations were found during continental days. SO4 2-, Cl- and NO3 - were found to be high during PD1 and PD2 days. Very good correlations of NH4+ with Cl- and SO4 2- ions in PD1 days indicate their common sources of origin and formation of ammonium chloride and ammonium sulphate. Water Soluble Inorganic Carbon (WSIC) was found during all dust days, Water Soluble Organic Carbon (WSOC) was found to be highest during PD1 and PD2 days. © Taiwan Association for Aerosol Research.

Aerosol and Air Quality Research

Chemical characterization of summertime dust events at Kanpur: Insight into the sources and level of mixing with anthropogenic emissions

The optical, chemical, and physical properties of dust over the Indo-Gangetic basin are presented based on a campaign mode experiment conducted at Kanpur (26.52oN, 80.23oE), India, during April to July, 2011. During the study period, heavy dust storms and onset of south-west Indian Monsoon occurred. Based on physico-chemical characteristics, four aerosol types were identified in the region: background aerosol, dust dominated aerosol, pollution dominated aerosol, and mixed aerosol. The classification of aerosol types was found to be consistent with various aerosol properties examined and backtrajectory analysis. In addition to the locally generated aerosols, there were both short and long range transported aerosols. Aerosols of oceanic origin were encountered during late June, and July. © 2014 Elsevier Ltd.

An overview of the physico-chemical characteristics of dust at Kanpur in the central Indo-Gangetic basin

The number concentrations of cloud condensation nuclei (CCN) and submicron aerosols (CN), along with their chemical composition and optical properties, have been studied during October 2008, October-November 2009 and November 2010 from an urban (Kanpur) site in the Indo-Gangetic Plain (IGP). The concentrations of CCN and CN and their optical properties vary with primary emission and secondary aerosol formation. The CCN (at 0.38% super-saturation) and CN concentrations varied from ~3900 to 15,000cm-3 and ~23,000 to 99,000cm-3, respectively. The diurnal variability of CCN and CN show peak concentrations during early morning hours (6:00-9:00 AM) and nighttime (7:00-10:00 PM), attributable to variability in source strength of carbonaceous aerosols and secondary aerosol formation. The CCN and CN concentrations are ~50% higher during nighttime with simultaneous increase in organic carbon (OC), elemental carbon (EC) and NO3- mass concentrations. However, CCN/CN ratios are similar during day and nighttime suggesting their co-variability with primary and secondary aerosol formation. The CCN/CN ratios are relatively lower (range: 0.11-0.33) than global average value and those over urban areas (with similar chemical composition in China and around the world) suggesting suppressed activation and hygroscopic growth in highly polluted environment of the IGP. The average mass absorption efficiency of EC during daytime (11.7±2.5m2g-1) is about factor of two higher than that during nighttime (5.7±1.3m2g-1). These results have implications to study morphological features, mixing state and microphysical properties of aerosols under high acidic environment over northern India. © 2014 Elsevier Ltd.

Primary and secondary aerosols from an urban site (Kanpur) in the Indo-Gangetic Plain: Impact on CCN, CN concentrations and optical properties

In-situ aircraft measurements of cloud condensation nuclei (CCN) and aerosol size distribution were carried out over the region spanning from 24.78 °N to 29.5 °N and 78.1 °E to 85.0 °E from June 29 to July 3, 2009 during the Indian Continental Tropical Convergence Zone (CTCZ) campaign, consisting of total 9 flight sorties. CCN measurements were conducted at a constant supersaturation (SS) of 0.84%. It was found that at higher altitudes (4.7-6.7km), 30nm sized particles were dominating while at lower altitudes (0.6-3.7km), 50nm particles. Overall, CCN closure ratio (CCNpredicted/CCNmeasured) at different altitudes using Köhler theory and assuming pure ammonium sulfate was 1.375 (R2=0.80). For each sortie, the closure ratio varied with height and depended greatly on measured CN concentrations. A case study of Khajuraho sortie showed that the closure ratio increased from 1.07 to 1.40 as the CCN concentration increased from 1000cm-3 to 4000cm-3. Results of CCN closure improved significantly (overprediction improved by 37.5% and 34.6% for Pantnagar and Gaya, respectively) with the assumption of internally mixed aerosols composed of ammonium sulfate and insoluble organics. Hygroscopicity parameter calculated for these two sorties (κ=0.51 and 0.5) indicates the presence of moderately hygroscopic organic species along with some inorganic content. © 2013 Elsevier B.V.