Sailesh N. Behera

Ammonia in the atmosphere: a review on emission sources, atmospheric chemistry and deposition on terrestrial bodies

Gaseous ammonia (NH3) is the most abundant alkaline gas in the atmosphere. In addition, it is a major component of total reactive nitrogen. The largest source of NH3 emissions is agriculture, including animal husbandry and NH3-based fertilizer applications. Other sources of NH3 include industrial processes, vehicular emissions and volatilization from soils and oceans. Recent studies have indicated that NH3 emissions have been increasing over the last few decades on a global scale. This is a concern because NH3 plays a significant role in the formation of atmospheric particulate matter, visibility degradation and atmospheric deposition of nitrogen to sensitive ecosystems. Thus, the increase in NH3 emissions negatively influences environmental and public health as well as climate change. For these reasons, it is important to have a clear understanding of the sources, deposition and atmospheric behaviour of NH3. Over the last two decades, a number of research papers have addressed pertinent issues related to NH3 emissions into the atmosphere at global, regional and local scales. This review article integrates the knowledge available on atmospheric NH3 from the literature in a systematic manner, describes the environmental implications of unabated NH3 emissions and provides a scientific basis for developing effective control strategies for NH3.

2013 Southeast Asian Smoke Haze: Fractionation of Particulate-Bound Elements and Associated Health Risk

Recurring biomass burning-induced smoke haze is a serious regional air pollution problem in Southeast Asia (SEA). The June 2013 haze episode was one of the worst air pollution events in SEA. Size segregated particulate samples (2.5-1.0 μm; 1.0-0.5 μm; 0.5- 0.2 μm; and <0.2 μm) were collected during the June 2013 haze episode. PM2.5 concentrations were elevated (up to 329 μg/m(3)) during the haze episode, compared to those during the nonhaze period (11-21 μg/m(3)). Chemical fractionation of particulate-bound trace elements (B, Ca, K, Fe, Al, Ni, Zn, Mg, Se, Cu, Cr, As, Mn, Pb, Co, and Cd) was done using sequential extraction procedures. There was a 10-fold increase in the concentration of K, an inorganic tracer of biomass burning. A major fraction (>60%) of the elements was present in oxidizable and residual fractions while the bioavailable (exchangeable) fraction accounted for up to 20% for most of the elements except K and Mn. Deposition of inhaled potentially toxic trace elements in various regions of the human respiratory system was estimated using a Multiple-Path Particle Dosimetry model. The particle depositions in the respiratory system tend to be more severe during hazy days than those during nonhazy days. A prolonged exposure to finer particles can thus cause adverse health outcomes during hazy days. Health risk estimates revealed that the excessive lifetime carcinogenic risk to individuals exposed to biomass burning-impacted aerosols (18 ± 1 × 10(-6)) increased significantly (P < 0.05) compared to those who exposed to urban air (12 ± 2 × 10(-6)).

Human health risk associated with exposure to toxic elements in mainstream and sidestream cigarette smoke

Toxic particulate elements present in cigarette smoke pose health threats to the life of smokers due to direct inhalation and at the same time increase health risks to non-smokers present in the vicinity of smokers because of their exposure. This study conducted a series of experiments using a controlled experimental chamber, equipped with simulated smoking conditions for characterization of particulate trace elements in mainstream and sidestream cigarette smoke. Four popular commercial cigarette brands available in Singapore market were used in this study. The target elements for extraction and analysis were Al, As, B, Ba, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Fe, Ga, Hg, K, Li, Mg, Mn, Na, Ni, Pb, Rb, Se, Sn, Sr, Te, Tl and Zn of both water-soluble and total constituents. The human health risk assessment results showed that the sidestream smoke had higher concentrations of toxic elements than those in the mainstream smoke. However, risk assessment analysis revealed that the sidestream smoke resulted in less human health risks compared to the mainstream smoke due to the influence of dilution of particulate emissions in sidestream smoke prior to inhalation exposure experienced by non-smokers. The cumulative non-cancer and cancer risks of toxic elements varied from 2.0 to 3.1 and from 398.4×10(-6) to 626.1×10(-6) due to inhalation of cigarette smoke by an active smoker. In the case of non-smokers, the risks were estimated under three possible cases of exposure. The cumulative cancer risks under three different cases were greater than the permissible limits. Therefore, it could be concluded that the toxic particulate elements present in cigarette smoke have significant carcinogenic and non-carcinogenic health effects due to inhalation exposure in the environment.

A study of diurnal variations of PM2.5 acidity and related chemical species using a new thermodynamic equilibrium model.

Aerosol acidity is one of the most important parameters that can influence atmospheric visibility, climate change and human health. Based on continuous field measurements of inorganic aerosol species and their thermodynamic modeling on a time resolution of 1h, this study has investigated the acidic properties of PM2.5 and their relation with the formation of secondary inorganic aerosols (SIA). The study was conducted by taking into account the prevailing ambient temperature (T) and relative humidity (RH) in a tropical urban atmosphere. The in-situ aerosol pH (pH(IS)) on a 12h basis ranged from -0.20 to 1.46 during daytime with an average value of 0.48 and 0.23 to 1.53 during nighttime with an average value of 0.72. These diurnal variations suggest that the daytime aerosol was more acidic than that caused by the nighttime aerosol. The hourly values of pH(IS) showed a reverse trend as compared to that of in-situ aerosol acidity ([H(+)]Ins). The pH(IS) had its maximum values at 3:00 and at 20:00 and its minimum during 11:00 to 12:00. Correlation analyses revealed that the molar concentration ratio of ammonium to sulfate (R(N/S)), equivalent concentration ratio of cations to anions (RC/A), T and RH can be used as independent variables for prediction of pH(IS). A multi-linear regression model consisting of RN/S, RC/A, T and RH was developed to estimate aerosol pH(IS).

Advances on transition metal oxides catalysts for formaldehyde oxidation: A review

ABSTRACT This article highlights recent advances in the development of transition metal-based catalysts for formaldehyde oxidation, particularly the enhancement of their catalytic activity for low-temperature oxidation. Various factors that enhance low-temperature activity are reviewed, such as morphology and tunnel structures, synthesis methods, specific surface area, amount and type of active surface oxygen species, oxidation state, and density of active sites are discussed. In addition, catalyst immobilization for practical air purification, reaction mechanism of formaldehyde oxidation, and the reaction parameters affecting the overall efficiency of the reaction are also reviewed.

Influence of Biomass Burning on Temporal and Diurnal Variations of Acidic Gases, Particulate Nitrate, and Sulfate in a Tropical Urban Atmosphere

The present study investigated the temporal and diurnal distributions of atmospheric acidic gases (sulphur dioxide (SO2), nitrous acid (HONO), and nitric acid (HNO3)) and those of particulate nitrate () and sulfate () through a comprehensive field campaign during the largest smoke haze episode in Singapore, a representative country in Southeast Asia (SEA). To identify the atmospheric behavior of these pollutants during the smoke haze period, the data generated from the measurement campaign were divided into three distinct periods: prehaze, during haze, and posthaze periods. The 24 hr average data indicated that ambient SO2, HONO, and HNO3 during the smoke haze episodes increased by a factor ranging from 1.2 to 2.6 compared to those during the prehaze and posthaze periods. Similarly, in the case of particulates and , the factor ranged from 2.3 to 4.2. Backward air trajectories were constructed and used to find the sources of biomass burning to the recurring smoke haze in this region. The air trajectory analysis showed that the smoke haze episodes experienced in Singapore were influenced by transboundary air pollution, caused by severe biomass burning events in the islands of Indonesia.

In situ acidity and pH of size-fractionated aerosols during a recent smoke-haze episode in Southeast Asia

The characterization of aerosol acidity has received increased attention in recent years due to its influence on atmospheric visibility, climate change and human health. Distribution of water soluble inorganic (WSI) ions in 12 different size fractions of aerosols was investigated under two different atmospheric conditions (smoke-haze and non-haze periods) in 2012 using the Micro-Orifice Uniform Deposit Impactor (MOUDI) and nano-MOUDI for the first time in Singapore. To estimate the in situ acidity ([H+]Ins) and in situ aerosol pH (pHIS), the Aerosol Inorganic Model version-IV under deliquescent mode of airborne particles was used at prevailing ambient temperature and relative humidity. The study revealed an increase in the levels of airborne particulate matter (PM) mass and concentrations of WSI ions for all size fractions during the smoke-haze period, which was caused by the trans-boundary transport of biomass burning-impacted air masses from Indonesia. A bimodal distribution was observed for concentrations of SO42−, NO3−, Cl−, K+ and Na+, whereas concentrations of NH4+, Ca2+ and Mg2+ showed a single mode distribution. The concentration of WSI ions in PM1.8 during the smoke-haze period increased by 3.8 (for SO42−) to 10.5 (for K+) times more than those observed during the non-haze period. The pHIS were observed to be lower during the smoke-haze period than that during the non-haze period for all size fractions of PM, indicating that atmospheric aerosols were more acidic due to the influence of biomass burning emissions. The particles in the accumulation mode were more acidic than those in the coarse mode.

Development of GIS-Based Optimization Method for Selection of Transportation Routes in Municipal Solid Waste Management

The municipal bodies in Indian megacities are facing several problems to maintain a good management practice with the massive solid wastes generated at all corners of large cities. This unique study used inbuilt optimization techniques and self-modified algorithms of the network analyst tool in the platform of Geographical Information System (GIS) to propose the optimized paths for municipal solid waste (MSW) collections at Kanpur, India. The input parameters used in modeling exercise were geographical location of waste points, existing road network, proposed transport routes, and locations of the dumping yards. The zone with eighteen wards having thirty-three locations for collection and two transfer stations for disposal of MSW was used as a test bed for the simulation exercise. All the locations were modeled separately to find respective optimized collection routes for solid waste management. This study found the reductions in haul distance as 27.78 ± 10.2% for the selected network.

The Air Quality Influences of Vehicular Traffic Emissions

The number of automobiles has been steadily increasing in cities as a consequence of rapid urbanization and economic growth. It has been widely reported that vehicular emissions are strongly correlated with the level of urban air pollution. The major primary air pollutants that are linked to direct emissions from on‐road vehicles include soot (black carbon), carbon monoxide (CO), and nitric oxide (NO). Human exposure to these air pollutants is of health concern. Therefore, it is important to investigate air pollutants of traffic origin (e.g., BC, CO, and NO) in ambient air at different locations of cities and to assess the effects of vehicles on the urban air quality. With this goal in mind, we carried a systematic study in Singapore (the fourth most densely populated country in the world) with concurrent measurements of BC, NO, and CO in ambient air at four different locations having variations in traffic flows and meteorology. We then assessed the relationship between traffic flows and prevailing levels of the three air pollutants, and studied the association of these air pollutants among each other and with diverse meteorological conditions. The major outcomes of the study are discussed.