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

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 (NO3-) and sulfate (SO42-) 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 SO42- and NO3-, 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

Assessment of Personal Exposure to Particulate Emissions in Urban Microenvironments

The levels of fine (PM2.5), derived from combustion sources, in both outdoor and indoor environments within cities can be very high and are therefore of health concern. In recent years, the focus of several air pollution studies has shifted from PM2.5 to other urban pollutants such as Black Carbon (BC) and ultrafine particles (UFP) due to their association with negative health effects. BC is a light-absorbing component of PM, and a good indicator of exposure to harmful particulate-bound chemical substances such as polycyclic aromatic hydrocarbons (PAHs) emitted from combustion sources such as urban vehicular traffic. UFP (those with aerodynamic diameter less than 0.1 μm) may be more toxic than PM2.5 due to their enhanced pulmonary deposition efficiency and much higher surface area. We assessed the personal exposure to PM2.5, UFPs and BC in diverse outdoor and indoor microenvironments (MEs) in Singapore. Since individuals are always on the move, it is important to follow their activity patterns, which determine their actual exposure. Consequently, a GPS was used to track individual’s movement and exposure across MEs. Potential health risks associated with inhalation exposure to airborne particles were estimated. The findings obtained from the study can be useful for citizens to make informed choices to reduce their exposures to particulate pollution in both outdoor and indoor environments. In addition, the study outcomes provide a scientific basis for the government to implement effective mitigation measures to lower people’s exposure to airborne particles at the city scale, contributing to improved urban air quality and enhanced health benefits

Your Course to College 2016-17

Iowa College Aid Your Course to College 2016-1

Comparison of physical and chemical properties of ambient aerosols during the 2009 haze and non-haze periods in Southeast Asia

Recurrent smoke-haze episodes that occur in Southeast Asia (SEA) are of much concern because of their environmental and health impacts. These haze episodes are mainly caused by uncontrolled biomass and peat burning in Indonesia. Airborne particulate matter (PM) samples were collected in the southwest coast of Singapore from 16 August to 9 November in 2009 to assess the impact of smoke-haze episodes on the air quality due to the long-range transport of biomass and peat burning emissions. The physical and chemical characteristics of PM were investigated during pre-haze, smoke-haze, and post-haze periods. Days with PM2.5 mass concentrations of ≥35 μg m−3 were considered as smoke-haze events. Using this criterion, out of the total 82 sampling days, nine smoke-haze events were identified. The origin of air masses during smoke-haze episodes was studied on the basis of HYSPLIT backward air trajectory analysis for 4 days. In terms of the physical properties of PM, higher particle surface area concentrations and particle gravimetric mass concentrations were observed during the smoke-haze period, but there was no consistent pattern for particle number concentrations during the haze period as compared to the non-haze period except that there was a significant increase at about 08:00, which could be attributed to the entrainment of PM from aloft after the breakdown of the nocturnal inversion layer. As for the chemical characteristics of PM, among the six key inorganic water-soluble ions (Cl−, NO3 −, nss-SO4 2−, Na+, NH4 +, and nss-K+) measured in this study, NO3 −, nss-SO4 2−, and NH4 + showed a significant increase in their concentrations during the smoke-haze period together with nss-K+. These observations suggest that the increased atmospheric loading of PM with higher surface area and increased concentrations of optically active secondary inorganic aerosols [(NH4)2SO4 or NH4HSO4 and NH4NO3] resulted in the atmospheric visibility reduction in SEA due to the advection of biomass and peat burning emissions

Importance of transboundary transport of biomass burning emissions to regional air quality in Southeast Asia during a high fire event

10.5194/acp-15-363-2015Atmospheric Chemistry and Physics151363-37

The chemistry of meteoric metals in the upper atmosphere

The metals Na, Li, K, Ca and Fe have been observed around 90 km in the earth\u27s upper atmosphere. Meteoric ablation is believed to be the source of these metals. The mesospheric chemistry of these metals and their impact on the general chemistry of the atmosphere are poorly understood. Therefore, a detailed investigation of processes affecting the gas-phase chemistry of these metals was undertaken.Both kinetic and photochemical studies were carried out using the techniques of pulsed photolysis of a suitable metal precursor and laser induced fluorescence of the resulting metal atoms. Ab initio calculations were also carried out to study the geometries of the metallic species and calculate their thermochemical properties.Kinetic investigations on the recombination reactions of the alkali metals with O\sb2 were performed over an extended temperature range (230-1100 K) in an attempt to understand their different seasonal behavior. The three reactions have very similar temperature dependences over the experimental temperature range. Use of the Troe formalism indicates that this dependency will continue into the mesospheric temperature range (140-240 K). The similarity suggests that differences in the temperature dependence of these reactions are not responsible for the different seasonal behavior of the alkali metals.The lower limits for the bond energies of the alkali superoxides were estimated from the kinetic decays obtained at 1100 K, and then combined with ab initio calculations to yield recommended bond energies. These values are of use in the Troe formalism and the mesospheric models.To assess the effectiveness of NaO\sb2 as a daytime sink, the absolute cross-section for photodissociation of NaO\sb2 was measured at 230 K. The photolysis rate of NaO\sb2 was derived above 70 km. The results indicate that above 85 km the reaction between NaO\sb2 and O is a more important loss term for NaO\sb2 than daytime photolysis and that between 80 and 65 km the photolysis of NaO\sb2 is the dominant loss term. From the photolysis experiment, an atmospherically important new Na species, NaO\sb4, was identified.The bimolecular reactions of Na with HCl/DCl, N\sb2O, and Li with H\sb2O were investigated. The possible role of the reaction between NaCl and H in the chlorine catalyzed destruction of O\sb3 was explored.Finally, the role of the reactions of dissociative electron attachment to NaHCO\sb3 and NaCO\sb3 in the formation of sudden sodium layers above 90 km was examined by ab initio and thermochemical calculations. The results indicate that NaHCO\sb3, an unreactive species in the mesosphere, can result in the formation of SSLs on collision with energetic auroral electrons