Sachin S Gunthe

This study provides baseline information about indoor-outdoor PM concentrations, size-resolved bioaerosol concentration, size distribution and diversity, I/O ratios of PM and bioaerosol, indoor bioaerosol emissions for five locations such as laboratory, students’ office, air-conditioned room, eatery, and residence. While most of the indoor air quality studies reported so far emphasized on a distinct type of indoor environment at a time, this study provides a first-hand account about PM and bioaerosols simultaneously measured and compared from diverse yet commonly encountered indoor locations of southern Indian region. PM2.5 and PM10 was found to have similar concentration distributions at all locations. Elevated cooking activity and human induced floor resuspensions led to the highest indoor-outdoor number concentration of PM at eatery. The I/O mass concentration ratios indicated the influence of outdoor PM on indoor environment of laboratory. Presence of distinct sources that contributed to significant PM mass variations at indoor and outdoor environments were substantiated with ANOVA and chi-square test results. Human occupancy and potted plants was found contributing to the elevated indoor bacterial concentrations (>800 CFU m−3). Fine to coarse bioaerosol fractions implied the abundant presence of coarse mode bacteria and fungi amounting to >80% of total cultivable bioaerosol load across all locations. Bacilli and Gammaproteobacteria dominated the bacterial aerosols while Cladosporium and Aspergillus dominated the fungal aerosols. Fungi contributed highest to the mass fraction of PM10 in comparison to bacteria, both indoor and outdoor. Highest bacterial emission rates were observed at air-conditioned room (4.85 × 105 CFU/h/person) and fungal emissions at laboratory (4.60 × 105 CFU/h/person).

Evaluating and quantifying the scientific output of a researcher is a complex problem that may not benefit from standardized or uniformly accepted solutions. Over the past few decades, various indices, including the most popular h-index, have been introduced for assessing the output and quality of research publications. The uniform application of a single index to researchers with varying age, tenure, gender, economies, funding opportunities, nature of tasks performed, etc., can introduce significant bias, eventually leading to inappropriate assessment results for promotion and tenure. Further, no indices explicitly account for the time spent on teaching-related tasks, advising students for their projects not necessarily resulting in publications, and administration work leading to a situation that favors colleagues who are focused only on research. A new metric, called GG-index, for internal use by institutions of higher education, is proposed to evaluate researchers who have spent a minimum of five continuous years at the academic/research institution. This GG-index is calculated from the h-index, the logarithm of the scientific tenure, citations/paper over the recent 5-year period, and a correction factor that considers the relative dedication to research and the researcher’s field. A survey was conducted of some top researchers in various fields, and their publication parameters and responses are used to illustrate the robustness and characteristics of the GG-index. We further demonstrate how the GG-index complements the h-index and helps mitigate the bias against researchers with long-term breaks for maternity, childcare, and other personal reasons. Further, young researchers with good recent publication impact (reflected by high citations per paper) and those working in fields with low citations would also be benefited. It is, however, to be noted that the GG index strongly relies on data available with the institutions, thus making it suitable for the internal assessment of faculty/researchers.

Size-resolved measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted over a full seasonal cycle at the remote Amazon Tall Tower Observatory (ATTO, March 2014-February 2015). In a preceding companion paper, we presented annually and seasonally averaged data and parametrizations (Part 1; Pöhlker et al., 2016a). In the present study (Part 2), we analyze key features and implications of aerosol and CCN properties for the following characteristic atmospheric conditions: Empirically pristine rain forest (PR) conditions, where no influence of pollution was detectable, as observed during parts of the wet season from March to May. The PR episodes are characterized by a bimodal aerosol size distribution (strong Aitken mode with DAit ≈ 70nm and NAit ≈ 160cm-3, weak accumulation mode with Dacc ≈ 160nm and Nacc ≈ 90cm-3), a chemical composition dominated by organic compounds, and relatively low particle hygroscopicity (ΚAit ≈ 0.12, Κacc ≈ 0.18). Long-range-transport (LRT) events, which frequently bring Saharan dust, African biomass smoke, and sea spray aerosols into the Amazon Basin, mostly during February to April. The LRT episodes are characterized by a dominant accumulation mode (DAit ≈ 80nm, NAit ≈ 120cm-3 vs. Dacc ≈ 180nm, Nacc ≈ 310cm-3), an increased abundance of dust and salt, and relatively high hygroscopicity (ΚAit ≈ 0.18, Κacc ≈ 0.35). The coarse mode is also significantly enhanced during these events. Biomass burning (BB) conditions characteristic for the Amazonian dry season from August to November. The BB episodes show a very strong accumulation mode (DAit ≈ 70nm, NAit ≈ 140cm-3 vs. Dacc ≈ 170nm, Nacc ≈ 3400cm-3), very high organic mass fractions (∼ 90%), and correspondingly low hygroscopicity (ΚAit ≈ 0.14, Κacc ≈ 0.17). Mixed-pollution (MPOL) conditions with a superposition of African and Amazonian aerosol emissions during the dry season. During the MPOL episode presented here as a case study, we observed African aerosols with a broad monomodal distribution (D ≈ 130nm, NCN, 10 ≈ 1300cm-3), with high sulfate mass fractions (∼ 20%) from volcanic sources and correspondingly high hygroscopicity (Κ < 100 nm ≈ 0.14, Κ > 100 nm ≈ 0.22), which were periodically mixed with fresh smoke from nearby fires (D ≈ 110nm, NCN, 10 ≈ 2800cm-3) with an organic-dominated composition and sharply decreased hygroscopicity (Κ < 150 nm ≈ 0.10, Κ > 150 nm ≈ 0.20). Insights into the aerosol mixing state are provided by particle hygroscopicity (Κ) distribution plots, which indicate largely internal mixing for the PR aerosols (narrow Κ distribution) and more external mixing for the BB, LRT, and MPOL aerosols (broad Κ distributions). The CCN spectra (CCN concentration plotted against water vapor supersaturation) obtained for the different case studies indicate distinctly different regimes of cloud formation and microphysics depending on aerosol properties and meteorological conditions. The measurement results suggest that CCN activation and droplet formation in convective clouds are mostly aerosol-limited under PR and LRT conditions and updraft-limited under BB and MPOL conditions. Normalized CCN efficiency spectra (CCN divided by aerosol number concentration plotted against water vapor supersaturation) and corresponding parameterizations (Gaussian error function fits) provide a basis for further analysis and model studies of aerosol-cloud interactions in the Amazon. .

Macrofungi have long been investigated for various scientific purposes including their food and medicinal characteristics. Their role in aerobiology as a fraction of the primary biological aerosol particles (PBAPs), however, has been poorly studied. In this study, we present a source of macrofungi with two different but interdependent objectives: (i) to characterize the macrofungi from a tropical dry evergreen biome in southern India using advanced molecular techniques to enrich the database from this region, and (ii) to assess whether identified species of macrofungi are a potential source of atmospheric PBAPs. From the DNA analysis, we report the diversity of the terrestrial macrofungi from a tropical dry evergreen biome robustly supported by the statistical analyses for diversity conclusions. A total of 113 macrofungal species belonging to 54 genera and 23 families were recorded, with Basidiomycota and Ascomycota constituting 96% and 4% of the species, respectively. The highest species richness was found in the family Agaricaceae (25.3%) followed by Polyporaceae (15.3%) and Marasmiaceae (10.8%). The difference in the distribution of commonly observed macrofungal families over this location was compared with other locations in India (Karnataka, Kerala, Maharashtra, and West Bengal) using two statistical tests. The distributions of the terrestrial macrofungi were distinctly different in each ecosystem. We further attempted to demonstrate the potential role of terrestrial macrofungi as a source of PBAPs in ambient air. In our opinion, the findings from this ecosystem of India will enhance our understanding of the distribution, diversity, ecology, and biological prospects of terrestrial macrofungi as well as their potential to contribute to airborne fungal aerosols.

An ultraviolet aerodynamic particle sizer (UV-APS) was continuously operated for the first time during two seasons to sample the contrasting winds during monsoon and winter to characterize the properties of fluorescent biological aerosol particles (FBAPs), at a high-Altitude site in India. Averaged over the entire monsoon campaign (1 June-21 August 2014), the arithmetic mean number and mass concentrations of coarse-mode (>ĝ€1ĝ€μm) FBAPs were 0.02ĝ€cmĝ'3 and 0.24ĝ€μgĝ€mĝ'3, respectively, which corresponded to ĝ1/4 ĝ€2 and 6ĝ€% of total aerosol loading, respectively. Average FBAP number size distribution exhibited a peak at ĝ1/4 ĝ€3ĝ€μm, which is attributed to the fungal spores, as supported by scanning electron microscope (SEM) images, and these results are consistent with previous studies made for FBAPs. During 11 weeks of measurements the variability of the total coarse-mode particle number (TAP) concentration was high compared to that observed in FBAP number concentrations. The TAP and FBAP number concentrations measured at this site were strongly dependent on changes in wind direction and rainfall. During periods of westerly/southwesterly winds with heavy persistent rainfall, the TAP and FBAP concentrations exhibited very low values (1.3 and 0.005ĝ€cmĝ'3, respectively) with no significant diurnal variations, whereas during periods of northerly winds with scattered rainfall FBAPs exhibited relatively high concentration values (0.05ĝ€cmĝ'3) with pronounced diurnal variations, which were strongly coupled with diurnal variations in meteorological parameters. The campaign-Averaged FBAP number concentrations were shown to correlate with daily patterns of meteorological parameters and were positively correlated with relative humidity (RH; R2ĝ€ Combining double low line ĝ€0.58) and negatively with temperature (R2ĝ€ Combining double low line ĝ€0.60) and wind speed (R2ĝ€ Combining double low line ĝ€0.60). We did not observe any significant positive correlation with precipitation as reported by previous researchers from selected areas. These measurement results confirm the fact that the ratio of PBAPs to TAP is strongly dependent on particle size and location and thus may constitute a significant proportion of total aerosol particles.

Many cities in India experience severe deterioration of air quality in winter. Particulate matter is a key atmospheric pollutant that impacts millions of people. In particular, the high mass concentration of particulate matter reduces visibility, which has severely damaged the economy and endangered human lives. But the underlying chemical mechanisms and physical processes responsible for initiating haze and fog formation remain poorly understood. Here we present the measurement results of chemical composition of particulate matter in Delhi and Chennai. We find persistently high chloride in Delhi and episodically high chloride in Chennai. These measurements, combined with thermodynamic modelling, suggest that in the presence of excess ammonia in Delhi, high local emission of hydrochloric acid partitions into aerosol water. The highly water-absorbing and soluble chloride in the aqueous phase substantially enhances aerosol water uptake through co-condensation, which sustains particle growth, leading to haze and fog formation. We therefore suggest that the high local concentration of gas-phase hydrochloric acid, possibly emitted from plastic-contained waste burning and industry, causes some 50% of the reduced visibility. Our work implies that identifying and regulating gaseous hydrochloric acid emissions could be critical to improve visibility and human health in India.

Dry deposition is a major sink for tropospheric ozone; nevertheless, studies on its effects on ozone distribution are very limited over the rapidly developing South Asian region. We performed numerical simulations using the regional model WRF-Chem (Weather Research and Forecasting Model coupled with chemistry) to investigate the effect of dry deposition on surface ozone over this region by switching dry deposition ON-OFF in the model. Dry deposition of ozone is found to reduce ozone mixing ratios by up to ∼ 40% over the Indo-Gangetic Plain (IGP) and parts of western and central India. Additional enhancements (by up to ∼ 5 ppbv) in ozone are simulated when dry deposition for all gaseous species is switched off. We find a significant contrast on the effects of dry deposition from station to station as well as on the diurnal timescales over this region. The enhancements in ozone, caused by the absence of dry deposition, are lower over urban stations during nighttime, as compared to the rural and high-altitude stations. Significant enhancements in ozone levels in the absence of dry deposition over the mostly agrarian IGP underpin the importance of dry deposition particularly in the vegetated areas. The South Asian ecosystem is seen to act as an important sink of surface ozone via the dry deposition. The analyses partially fill a gap in the studies of dry deposition over the South Asian region, where this sink is anticipated to get perturbed following the changes in land use and land cover.

We evaluate numerical simulations of surface ozone mixing ratios over the south Asian region during the pre-monsoon season, employing three different emission inventories in the Weather Research and Forecasting model with Chemistry (WRF-Chem) with the second-generation Regional Acid Deposition Model (RADM2) chemical mechanism: the Emissions Database for Global Atmospheric Research - Hemispheric Transport of Air Pollution (EDGAR-HTAP), the Intercontinental Chemical Transport Experiment phase B (INTEX-B) and the Southeast Asia Composition, Cloud, Climate Coupling Regional Study (SEAC4RS). Evaluation of diurnal variability in modelled ozone compared to observational data from 15 monitoring stations across south Asia shows the model ability to reproduce the clean, rural and polluted urban conditions over this region. In contrast to the diurnal average, the modelled ozone mixing ratios during noontime, i.e. hours of intense photochemistry (11:30-16:30gIST - Indian Standard Time - UTC +5:30), are found to differ among the three inventories. This suggests that evaluations of the modelled ozone limited to 24gh average are insufficient to assess uncertainties associated with ozone buildup. HTAP generally shows 10-30gppbv higher noontime ozone mixing ratios than SEAC4RS and INTEX-B, especially over the north-west Indo-Gangetic Plain (IGP), central India and southern India. The HTAP simulation repeated with the alternative Model for Ozone and Related Chemical Tracers (MOZART) chemical mechanism showed even more strongly enhanced surface ozone mixing ratios due to vertical mixing of enhanced ozone that has been produced aloft. Our study indicates the need to also evaluate the O3 precursors across a network of stations and the development of high-resolution regional inventories for the anthropogenic emissions over south Asia accounting for year-to-year changes to further reduce uncertainties in modelled ozone over this region.

Bioaerosols abundantly found in the atmosphere can potentially influence the climate by acting as ice nuclei and thus profoundly influencing the hydrological cycle. As the first attempt over India, we report the diversity, abundance, and ice nucleating ability of bacteria present in the rainwater collected at Chennai, during summer and two contrasting monsoon seasons. Diverse bacterial communities were present in all the twenty rainwater samples and predominantly belonged to Actinobacteria (6%), Alpha proteobacter (9%), Bacilli (29%), Betaproterobacteria (14%), Flavobacteria (3%), and Gammaproteobacteria (39%). The most efficient ice nucleating bacteria such as Pseudomonas sp. and Pantoea sp. were present in our precipitation samples and they contributed to 8.4% and 9.4% of the total cultivable bacterial species obtained. The relative abundance of Pseudomonas was highest during the south-west monsoon (75%) whereas Pantoea was abundant in the north-east monsoon (51.8%). The dominant bacteria belonging to the known ice nucleating genera Pseudomonas, Pantoea, and Bacillus were chosen for the determination of their freezing temperatures using tube freeze assay technique. The onset freezing temperature of species belonging to Pseudomonas and Pantoea was recorded as −12 °C and for those species belonging to Bacillus it was found to be −14 °C. Further, the number of bacterial cells making up an ice nucleus was estimated at the temperatures ranging from −18 °C to −12 °C for all the ice nucleating bacteria and it was found to vary from 106 to 109 (cells/nucleus).

Aerosol Liquid Water Content (ALWC), a ubiquitous component of atmospheric aerosols, modulates atmospheric chemistry through aerosol surface reactions and reduces the atmospheric visibility. However, the complex dependency of ALWC on aerosol chemistry and relative humidity (RH) in the Indian region remains poorly characterized. Here, we combine available measurements of aerosol chemical composition with thermodynamic model, ISORROPIA2.1, to reveal a comprehensive picture of ALWC in fine mode aerosols during the winter season over the Indian continental region. The factors modulating ALWC are primarily dependent on the RH, such that the effect of aerosol dry mass and hygroscopicity are significant at high RH while the effect of hygroscopicity significantly reduces with decreasing RH. ALWC is observed to display a sharp non-linear rise, beyond a critical value of ambient RH dependent on the particle hygroscopicity. Further analysis by coupling Weather Research Forecasting-Chem simulation with ISORROPIA2.1 revealed significant spatial heterogeneity in ALWC over India, strongly associating with regions of high aerosol mass loading and RH. The Indo-Gangetic Plain is consequently observed to be a hotspot of higher ALWC, which explains the prevalent conditions of haze and smog during winter in this region. Our findings re-emphasize that high aerosol mass resulting from intense pollution is vital in modulating aerosol–climate interaction under favorable meteorological conditions. Observations suggest the need for localized pollution control strategies, directed at the reduction in aerosol emissions of specific chemical composition observed to contribute to the enhancement in PM through an increase in ALWC during wintertime in the region.