# INTRODUCTION esearch work had been carried out in the past to investigate the influence of ambient temperature on exhaust emissions [1 -14]. It was reported that exhaust emissions could be increased tremendously at cold ambient conditions. For instance, the hydrocarbon emissions could increased by 650% at -20 o C and carbon monoxide emissions could increased by 800% at -20 o C, compared to standard certification values at +25 o C [8,9]. However, the influence of cold temperatures on NOx was much lower and more complex as cold temperatures increase engine heat losses and cool the flame, thus reducing NOx emissions from the engine. This partially offset the slower catalyst light off. The low ambient temperature can reduce lubricating oil pumpability and increase viscosity of lubricating oil and thus results in higher mechanical losses for engine's cold start. The performance of the battery would be affected by low ambient temperature. The air and fuel mixture can be affected due to poor volatility of fuel at low ambient temperature and therefore cause deterioration of combustion quality. The lower the ambient temperature, the richer the air fuel mixture required for a start up. Incomplete combustion with excess fuel results in increased carbon monoxide and hydrocarbon emissions. The low ambient temperature can also delay the light-off of the catalyst, which is one of the most important reasons accounting for high emissions at cold start. The literature above reveals the influence of ambient temperature on vehicular emissions at 'cold start' period only. However not much work has been done to investigate the variation of vehicular emissions with ambient temperature and humidity at both the morning and afternoon periods, which entails the cold start and warm-up period of the engine. With a unique approach, this study investigates the variation of vehicular emissions with ambient temperature and humidity in the tropics by considering both the morning and afternoon period for exhaust emission measurements and analysis. # II. # METHOD OF INVESTIGATION Certain exhaust samples were collected from a number of vehicle engines (that use Motor Premium Spirit) and analyzed using the Exhaust Gas Analyzer with Model number "Testo 350 XL". These samples were collected during the morning (low temperature and high humidity) and afternoon (high temperature and low humidity) periods. A temperature and humidity sensing device (Digital Thermometer/Hygrometer with Model number IT 202) was used to measure both temperature and humidity during those periods. The investigation was carried out in some parts of Edo State of Nigeria and thereafter mathematical models and graphical representation of the investigations were obtained using MATLAB. (See table 1) # RESULTS AND DISCUSSION Using linear and quadratic fitting of the MATLAB code, the following mathematical and graphical models for CO, CxHy, and NOx emissions were obtained; b) NOx Emissions Figure 3 above shows the Nitrogen Oxides emissions as a function of the temperature. The result of figure 3 above shows that the "engine out NOx emissions" are reduced in the morning period when the ambient temperature is very low, but increased during the afternoon period when the ambient temperature was high. This implies that the increase of NOx emission is directly proportional to the ambient temperature. The reason for this is that NOx is a temperature dependent pollutant as it is formed in the combustion chamber when the combustion temperature increases to 2000 o C [3]. This means that, as the temperatures decreases, the engine heat loss increases thereby cooling the flame temperature and therefore reducing the amount of NOx released from the engine exhaust. The mathematical model and graphical representations of the pollutants against the humidity (H) are shown below; # Figures of 4 & 5 show Carbon Monoxide and Hydrocarbon emissions as functions of humidity. It is observed that when the humidity is very high, the concentration of the pollutants (CO & CxHy) will also be high and when the amount of humidity present in the atmosphere is very low, the concentration will automatically be low. The reason for this is that high amount of humidity in the atmosphere can cause poor mixing of fuel and air in the combustion chamber, thereby resulting in incomplete combustion which will in turn results in excessive release of CO and CxHy pollutants [5]. The case is the reverse for NOx emissions of figure 6 above as high humidity will result in the reduction of NOx pollutants released from the engine exhaust. The reason for these has been explain in the previous paragraph of this study. # CONCLUSION Investigations carried out in this study tend to show that vehicular emissions vary with ambient temperature and humidity at different times of the day. There seem to be much increase in emission rates when the ambient temperature falls below the standard temperature of 75 o F, this might be due to "cold start problem of the vehicle engine". It could also be that it takes a long time for the emission control system (catalytic converter) to warm up, indicating that more fuel is required in the combustion chamber for smooth combustion (rich fuel/air mixture). The findings from this study have shown high concentration of CO and CxHy pollutants during the early morning periods when the engine is just warming up, and high concentration of NOx emissions during the afternoon period when the engine is fully warmed up. These pollutants are capable of causing harm to the environment by contributing to the formation of smog, ground level ozone and global warming. 12![Fig 1 : Graph of Predicted and Measured Values of Carbon Monoxide against Temperature.](image-2.png "Fig 1 :Fig 2 :F") 1and humidityTemperature ( o C)Humidity (%)26.97028.56429.26131.85433.449III. © 2012 Global Journals Inc. (US) * Emissions and air quality HansPeter ChristianCozzarini 2000 SAE Reference book R-237 * JLaurikko Erlandsson RArbrahamsson Exhaust in Cold Ambient Conditions 1995 * Considerations for a European Test Procedure. SAE Paper 95923 * The effect of Ambient Temperature on the Emissions of Some Nitrogen Coumpouds"; A Comparative Study on Low-Medium and High Mileage Three way Catalyst Vehicles JLaurikko PAakko 1995 SAE Paper 950933 * Predictability of emissions from In-Use Vehicles at Low-Ambient Temperature and Alternate Driving Cycle Based on Standard Tests MDGurney Allsup J. R 1989 SAE Paper 890625 * .R ELarson 1989 * Cold Start Impact on Vehicle Energy Use GWTaylor StewartS 2001 SAE Paper 01-0221 * The Effect of Ambient Temperature on Cold Start Urban Traffic Emissions for a real World SI Car GEAndrews HZhu Li ASimpson JAWylie Bell JTate 2004 SAE Paper 01-2903 * Regulated and Unregulated Emissions from Catalyst Vehicles at Low Ambient Temperature JLaurikko NNylund 1993 SAE Paper 930946 * Quantifying Vehicle Emission Factors for Various Ambient Conditions using an On-Road, Real-Time Emissions system DHJason MCheckel 2003 SAE Paper 01-0301 * Transient Heating and Emissions of an SI Engine during the Warm-up period GEAndrews JRHarris AQunzain 1988 SAE Paper 880264 * SI Engine Warm-up: Water and Lubricating Oil Temperature Influences GEAndrews JRHarris AQunzain 1989 SAE Paper 892103 * The Role of Cooling Water and Lubricating Oil Temperature on Transient Emissions during SI Engine Warm-up GEAndrews JRHarris AQunzain 1989 IMech. E. * Experimental Methods for Investigating the Transient Heating and Emissions of an SI Engine during the Warm-up Period GEAndrews JRHarris AQunzain 1988 Imech.E. * The Influence of External Heat Losses on the Transient SFC and Emissions during the warm-up period of an SI Engine GEAndrews JRHarris AQunzain 1990 * References Références Referencias