Experiment with exhaust from cars

This is a picture of Wafaa and Numan (two students) working with exhaust from a car. The first experiment we "fit" the exhaust with a full glass of CO2-indicator. It changed colour very fast. And it shows us that there is CO2 in the exhaust. Chemical reactions: CO2 + H2O > H2CO3 In the next experiment we did the same thing but with water. PH-value was 7 before we started the experiment. After a minute when this second and last experiment was finished. We found out that the pH-value was not changed. Asumption: We can make an asumption that there is NOxs in the car's exhaust: N2 + O2 > 2 NO Nitrogen + oxygen > nitrogenoxid 2 NO + O2 > 2 NO2 Nitrogenoxid + oxygen > nitrogendioxid 4 NO2 + O2 + 2 H2O > 4 HNO3 Nitrogendioxid + oxygen + water > salpetersyre