LITERATURE SURVEY
2.1. Characteristics of Hydrogen Sulphide
2.1.1. Physical and Chemical Properties
H2S is a colourless gas characterised by a rotten gas odour which is highly toxic. It is soluble in different liquids including water and alcohols. It is typically formed under deficit oxygen conditions in the presence of organic matter and sulphate compounds (WHO, 2003). Hydrogen Sulphide is also present in the atmosphere in the range of 0.0001-0.0002 ppm though it may vary with places and therefore goes unnoticed (WHO, 1981). The table gives description of physical and chemical properties of H2S:
Table 2.1: Properties of Hydrogen Sulphide (AIHA, 1991):
Description Hydrogen Sulphide
Molecular formula H2S
Molar mass 34.08g/mol
Boiling point -60.4 0C
Melting point -85.5 0C
Critical temperature 100.50C
Density 1.43g/m3
Short Term Exposure Limit(STEL) 5 ppm (15 min)
Immediate Damage to Life or Health (IDLH) 100 ppm
Vapour pressure 18.266 bar at 210C
Conversion factor 1ppm= 1.5 mg/m3
2.1.2. Health Effects
Hydrogen sulphide is an asphyxiant and irritant gas. Concentrations above a limit of 20 ppm might irritate the eyes and the respiratory tract, above 50-100 ppm have neurotoxic effects and concentrations above 100 ppm are considered of immediate life danger (WHO, 2003). H2S is a dense gas and it can accumulate in closed areas. Many of the fatal accidents have been accredited to the effect of H2Swhich is released by vents or through thermal springs (Martin-Duque et.al. 2006). The effect of H2S also depends on the amount of pollutants present, the duration of exposure, age and level of activity of a person. Even though studies of severe toxic effects of H2S are common but knowledge about the long term exposure effects is rare. The first visible effect of H2S at low concentrations is its odour followed by eye irritation (WHO, 2003).The following table gives dose effect relationships for hydrogen sulphide: Table 2.2: Dose effect relationship for hydrogen sulphide H2S concentration (ppm) Effect Reference 1000-2000 Immediate collapse with paralysis of respiration WHO, 1981 530-1000 Strong CNS stimulation, hyperpnoea followed by respiratory arrest WHO, 1981 320-530 Pulmonary oedema with risk of death WHO, 1981 150- 250 Loss of olfactory sense Ronk,R et al.,1985 50-100 Serious eye damage Ronk,R et al.,1985 10-20 Threshold for eye irritation Ronk,R et al.,1985 2.2. Basics of meteorology Meteorology is defined as the science of atmosphere in to which the pollutants are emitted. The knowledge of meteorology is used to manage and handle the release of pollutant into the ambient atmosphere. It gives us an idea of the fate and the transport of air pollutants. By proper management we can ensure that that the pollutant concentrations are in accordance with the air quality standards. 2.2.1 Atmosphere – Composition, Structure and Circulation 2.2.1.1. Composition of atmosphere The earth is surrounded by the atmosphere which rotates as earth orbits around the sun. Generally, dry air consists of about 78% nitrogen, 21% oxygen and 1% of other gases (argon, carbon dioxide, neon, helium and water vapour). Even though the composition of water vapour is very less as compared to other gases, it absorbs around six times more radiation than other atmospheric constituents and is therefore an important component of the atmosphere (Sheehy J.P.,et al.,1968). 2.2.1.2. Structure of the atmosphere The atmosphere is divided into four distinct layers: the troposphere, stratosphere, mesosphere and thermosphere. The lowest layer is called the troposphere which accounts for almost three quarters of the mass of atmosphere and it consists of all the water (vapour, clouds, and precipitation), air masses, fronts and storms. Due to these factors it is the most unsettled layer in the atmosphere and it provides earth its climate. The thickness of troposphere changes with latitude and season …show more content…
At this temperature, the water vapour condenses to form water and releases latent heat in the parcel. Due to this the cooling rate of the parcel slows down. This rate is called the wet adiabatic lapse rate. The wet adiabatic lapse rate is always less than the dry adiabatic lapse rate because the air parcel cools slower when heat is released. The wet adiabatic lapse is not constant and changes with temperature and pressure (Hanna,S.R.,et.al.,1982). However, the average value in the middle troposphere is taken approximately as -6 to -70C /