Essay Example on Non methane hydrocarbons NMHC









Non methane hydrocarbons NMHCs are a major class of organic pollutants Xiao and Zhu 2003 Caselli et al 2010 that significantly affect atmospheric photochemical chemistry and human health Elbir et al 2007 Mudliar et al 2010 The NMHCs and oxygenated NMHCs e g alcohols aldehydes and organic acids are constituents of volatile organic compounds VOC that have short atmospheric lifetimes fractions of a day to months and have direct but small impacts on atmospheric radiative forcing Intergovernmental Panel on Climate Change https www ipcc ch ipccreports tar wg1 140 htm NMHCs have an important role to play on air quality due to their high reactivity that enables them to generate tropospheric ozone O3 through atmospheric chemical reactions with nitrogen oxides NOx and radicals under relatively high NOx concentrations Fehsnfeld and Liu 1987 Finlayson Pitts and Pitts 2000 Batterman et al 2005 As O3 in many areas could be NMHC dependent controlling NMHC emissions has assumed great importance and has been imposed to attain O3 standards Batterman et al 2005 In rural areas where NOx concentration is generally small O3 production is also less But in the urban areas due to the industrial and vehicular pollution the relative concentration of NOx reaches up to a level so that it easily contributes to production of O3 even in small concentration of NMHCs Donahue and Prinn 1990 

The importance of NMHCs as O3 producing precursor through the OH radical initiated oxidation and subsequent reaction with NOx has been well studied Warnec 1988 In polluted areas with relatively high concentration of NOx photochemical oxidants of NMHCs initiate a complex series of photochemical reactions known as photochemical smog mechanism that leads to the production of O3 and other secondary oxidant pollutants Haggansmith 1952 Bowman and Seinfeld 1994 Because of their important role in the air quality and the formation of ozone the World Meteorological Organization Global Atmospheric Watch WMO GAW programme commenced to measure NMHCs and other reactive compounds in the global network WMO 2007 Sources of NMHCs in urban air are usually dominated by anthropogenic emissions including liquefied petroleum gas LPG leakages solvent usage and vehicular emissions Barletta et al 2005 Tang et al 2007 Duan et al 2008 power plants petrochemical plants oil refineries and chemical plants slash burning and even solid waste disposal Arya 1999 Barletta et al 2002 Vehicular emission is one of the major NMHC sources and their emissions from vehicles include refuelling losses starting emissions evaporative losses and tailpipe emissions Batterman et al 2005 

The other significant anthropogenic sources of NMHCs consist of petroleum products chemicals manufacturing industries painting operations varnishes coating operations consumer products petroleum handling auto refinishing cold clean degreasing printing inks dry cleaning etc Srivastava and Majumdar 2011 Tan et al 2011 reported that ethene ethane ethyne propane i pentane and toluene were the most abundant hydrocarbons in Foshan in China Generally most abundant hydrocarbons showed high mixing ratios in the morning 09 30 10 30 hours decreased to the lowest level in the afternoon 14 30 15 30 hours and increased to higher value in the evening 19 30 20 30 hours But i pentane exhibited a different diurnal pattern with the highest level 13 4 5 8 ppbv in the afternoon implying the acceleration of solvent evaporation resulting from higher temperature Vehicular emissions were found to be the main sources of ethene propene i butene isoprene benzene and toluene while gasoline evaporation was responsible for n pentane n hexane and n heptane It was suggested that LPG leakage was the main source of propane while natural gas leakage was responsible for ethane in Foshan City Tan et al 2011 Potential sources of greenhouse gases and various air pollutants in Nagpur Urban Agglomeration UA has been discussed at length before Majumdar and Gajghate 2012 Majumdar et al 2013 and some of these reported sources are also potential NMHC emitters 

Monitoring of total NMHC also known as TNMHC concentrations in ambient air has been undertaken sparsely from a few Indian cities Nishanth et al 2014 Sarkar 2015 Sharma et al 2016 and there are some reports on ambient concentrations of select individual NMHCs and VOCs also from a few Indian locations Sahu and Lal 2006 a b Purkait et al 2009 Srivastava and Mazumdar 2011 Majumdar et al 2015 Knowledge on ambient TNMHC concentrations could actually help formulate air quality management planning of a city Indian cities could be potential hotbeds of NMHCs due to variety of NMHC sources like vehicular traffic consisting of sizeable fleet of old vehicles small manufacturing units painting and varnishing workshops petrol pumps auto refinishing workshops etc and therefore it makes sense to assess ground level TNMHC concentrations over Indian cities This work was undertaken to measure TNMHC in ambient air of Nagpur one of the major and progressive cities of Central India over three seasons viz post monsoon September October winter January February and summer May June during 2013 2014 in a year long study Temporal diurnal and seasonal and spatial variation in TNMHC vis a vis the abundance of reported sources over the selected UA has been examined and reported Also mean TNMHC concentrations during weekdays and weekends over all seasons were extracted evaluated and compared

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