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The ultrafine and nano particles compared to larger particles are gaining high importance because of their vulnerable effects to environment and human health causing respiratory problems, cardiovascular disease, and various types of cancers leading to premature death [1]. WHO report points out that approximately, two thirds of the global burden of disease due to urban outdoor air pollution is mostly from the developing countries in Asia (Cohen et al. 2004)[2]. By number, nearly all of the particles emitted by a diesel engine are nanoparticles which are also true for gasoline engines [3]. This is addressed by new UN Regulations by introducing the emission norms for diesel and GDI vehicles for particle number and PM2.5 as 6 x 10 11 and 4.5 mg/km respectively [4]. However, other S.I. engines like CNG, even though they look clean as there is no visible smoke but emitting large number of particles is necessary to investigate. This research paper focuses on characterization of ultrafine and nano particle emissions from CNG vehicle on Indian driving cycle and it covers experimental Investigation to identify the significance of different operating phases viz. idling, acceleration, deceleration and cruising for their contributions to particle number and size distribution pattern over urban as well as on extra urban part of the cycle. CNG passenger car shows large peak of PN emissions during cold starting phase at the beginning of the test cycle which is almost twice that of diesel vehicle. However, this concentration peak will decrease near to 25% on light operating loads during urban part of the cycle, but during acceleration and cruising operation on extra urban cycle under heavy load the PN emissions from CNG car are higher in magnitude. The particles emitted from CNG buses are too small to contribute to PM10 as they are of ultrafine and nano size range.

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Today, in the automotive emissions ultrafine and nanoparticles emissions are of very high importance because of their vulnerable effects to environment and human health causing respiratory problems like bronchitis, asthma, cardiovascular disease, and various types of cancers spreading in all age groups in the society leading to premature death [1]. Therefore, characterization of ultrafine and nanoparticles in terms of their size distribution and number concentration for the automobiles operating on various fuels and traffic conditions is of great importance in understanding the phenomenon and the adverse effects. Various research studies carried out at international level show the adverse health effects due to ultrafine particles from C.I. and S.I. engines and hence, there is definite need to examine for the particulate mass, size and number concentration considering social needs [2].Even after very stringent emission norms which were tightened over the years and today down to more than 97% from it’s baseline norms couldn’t show proportionate improvement in the ambient air quality. Climate effects inevitably lead to health effects leading to premature death due to ultrafine particles from the automotive exhaust [1]. Recent WHO report confirmed the vulnerable effect of diesel particles in terms of carcinogenicity and severe health effects of diesel fuel used in automotive sector [3]. European regulations has taken the steps to address this concern by introducing new norms for particle number and PM2.5 as 6 x 1011 and 4.5 mg/km respectively [4]. Investigations carried out on GDI vehicles show substantial ultrafine and nanosize particle emissions and by number, nearly all of the particles emitted by a diesel engine are nanoparticles which are also true for gasoline engines [5]. Like gasoline engines other S.I. engines, even though they look very clean as there is no visible smoke and large particles emitted in their exhaust, it is necessary to investigate them. Very limited research work has been carried out particularly, on CNG engines/ vehicles for their PM and PN levels at national and international level. Characterization of ultrafine and nanoparticles in terms of their size distribution and number concentration for the automobiles operating on various fuels and traffic conditions is of great importance in understanding the phenomenon and their significance.In this context and understanding the social need this research work was carried out to investigate experimentally the significance of CNG and diesel passenger car for it’s contribution to particle number (PN) and PM2.5. This work includes comparative investigation of CNG and diesel passenger cars to characterize the ultrafine and nanoparticle emissions on modified Indian driving cycle. CNG passenger car show large peak of PN emissions during cold starting phase at the beginning of the test cycle which is almost twice that of diesel vehicle but it settles down to lower level as the vehicle gets warmed up. During acceleration and cruising operation on extra urban cycle under heavy load the PN emissions from CNG car are higher in magnitude. For diesel car, urban part of cycle contributes approximately 53% compared to 25% for CNG vehicle and rest 47% and 75% is contributed by extra urban part towards PN emissions.This research paper covers experimental Investigation carried out to compare the behavior of diesel and CNG passenger cars to characterize the particle emissions and to identify the significance of different operating phases viz. idling, acceleration, deceleration and cruising for their contributions to Particle number and size distribution pattern on urban and on extra urban part of the driving cycle.