Nitrogen oxides Essay
Nitrogen oxides occur in NO, NO2 N2O forms. They are formed by oxidation of diatomic nitrogen (N2 ) which makes up 78 percent of the total atmosphere. The air, temperature rises which trigger a chemical reaction between diatomic nitrogen to form Nitrogen oxide. N2 + O2 2NO The three nitrogen monoxide formed by combustion, persist in the atmosphere for an average of four days before it is oxidized by atmosphere ozone. NO +O3 NO2+O2 This reaction threatens the stratospheric O3 responsible for screening UV radiations from the sun.
The resultant NO2 undergoes hydrolysis to form nitric acid by reacting with water molecules in the atmosphere which fall as acid rain. 3NO2 + H2O 2HNO3 +NO The nitric acid rain brought down may first combine with ammonia (NH3 ) to form ammonium nitrate (NH4NO3) where it eventually becomes viable plant nutrient. Nitrogen oxides have tremendous effects on the environment especially in urban center endowed with high traffic volume. This is reflected on human health and biodiversity at large. They include –NO2 which is unusual among simple air pollutants because of its color which is brownish-yellow in appearance.
An NO2 level of one parts per million sometimes found in urban centers to reduce visibility to a distance of about 10 miles (Giddlings 1973). The compound NO is relatively inert and moderately toxic like carbon monoxide. It combines with hemoglobin forming metheglobin therefore reducing oxygen transport. Nitrogen dioxide is highly toxic and corrosive causing respiratory irritation and distress. NOx together with hydrocarbons are important precursors for the formation of tropospheric oxygen and other photochemical oxidants including peroxyacetyl nitrate.
This utilizes free hemoglobin in blood rendering it impossible and unable to ferry oxygen, hence the body is deprived of oxygen. HYDROCARBONS (VOC) “From their toxicological standpoint benzene is probably the most significant of the VOCs as documented in HIGHWAY POLLUTION by Ronald S Hamilton page 264. Aplastic anaemia (reduced red blood cells) occurs either through inhalation or skin contact with benzene. In serious benzene poisoning red blood cells, white blood cells and even platelets are affected a condition called Pancytopenia. The total benzene emissions increase with increase in benzene petrol levels and other aromatic fuel contents.
Use of alcohol particularly ethanol and methanol as fuel additives in hybrid vehicles have resulted into increased VOC load. Methanol using fuels have resultant effect in increasing formaldehyde that is regarded as carcinogenic. PHOTOCHEMICAL SMOG. Exhausts from hybrid vehicles produce oxidative pollutants which lead to photo chemical smog. These have effects on eye irritation. These reactions form ozone, peroxy acetyl nitrate and aldehydes and other compounds that may affect human health. O3 + hv O2 + O O + H2O 2OH NO2 +hv NO+O (3P) O (3P) + M O3 + M NO from NO2 photolysis reacts with ozone. O3 +NO2 NO2 + O2
K3[NO2] K5 [NO] [O3] [O3] k3/k5[NO2]/[NO] CO +OH CO2 + H H +O2 HO2 HO2 + NO NO2+ OH With high NO2 /NO ratio increase O3 concentration is predicted in the presence of good sunlight DISCUSSION PARTICULATE The reason for darkness of smoke in the atmospheric (air) is the presence of particulate elemental carbon (PEC) in the emissions from diesel smoke. PEC’s emission factors showed that diesel alone was responsible for between 84% and 95 % PEC Emissions for major towns “PEC is generally considered responsible for more than 90% of light absorption and 30% visibility reduction in the atmosphere” HIGHWAY POLLUTION page 18 by Ronald S.
Hammilton. The qualification of carbon dioxide in air and its origination from traffic source was done using emission inventory approach. The results indicate that vehicles are responsible for 24% of the carbon dioxide emissions. Diesel emission from hybrid which have been found to have mutagenic activity Lead To start up, air lead has been found to correlate with blood lead according to the department of environment in the UK. They concluded “in the UK exposure to lead from a number of sources was found to co relate with alterations on petroleum lead levels.
Lead toxicity is a major health hazard in children because of their rapid development. They cause reduction in cognitive scales hyper activity as documented from the second national health and nutrition examination survey (NHANES II) in the U. S. A. Manganese it is used in hybrid vehicles as methylecyclopentadienyl manganese tracarbonyl (MMT) as antiknock additives. It has minimal effects since emissions from hybrid vehicles. “In the US airborne manganese levels decreased approximately 50 percent between 71 and 1982. These reductions occur as a result of greater control of particulates from point sources”.
As documented in highway pollution by Ronald Hamilton page 271. Chronic exposure of manganese result into mangaism characterized by hallucinations and psychosis. CARBON MONOXIDE Carbon monoxide is odorless and colorless. Its effects as environmental hazards are bared on its property to combine with Hemoglobin of blood. Hemoglobin is an iron-containing protein that carries oxygen (O2) to body tissues. It picks up O2 in the lungs as shown below Hb + O2 O2 Hb (in the lungs) Hemoglobin in the lungs Released in tissues This is reversible association.
However if carbon monoxide enters the lungs, it replaces O2 by combining with Hemoglobin. Owing it to its diatonic form, CO is comparable to O2 and hence can replace it Hb + CO Carboxyl hemoglobin CH4 + OH CH + H2O CH3 + O2 CH3O2 2CH3O2 + 2CH3O + O2 CH3O2H +O2 CH3O + O2 HCHO +HO2 HCHO HCO + H HCHO CH3O + OH RCO + O2 RCO3 RCO3 +NO RCO3 + NO2 RCO2 R +CO2 R2C CR2 R2C CR2O R C CRO R2COH +R2CO Conclusion Emission from the internal combustion engine of a hybrid vehicle is a function of its fuel concentration and engine type.
However the ratio of fuel and air is the major factor in the operation of the system. The paper has identified the emissions from hybrid vehicles as carbon monoxide, carbon dioxide, VOCs, nitrogen oxides and particulate as the major pollutants. All this contribute to the general air pollution leading to toxicity in man.
REFERENCES 1. DETR, A New Deal For Tranport: better For Everyone, Tso press London, 1998. 2. www. sciencedirect. com journal on Atmospheric environment. 3. ATKINS R, Physical Chemistry by Mc grawHill press, 1999, USA.
Subject: NO2 N2O,
University/College: University of Arkansas System
Type of paper: Thesis/Dissertation Chapter
Date: 21 April 2017
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