In real world, diesel vehicle loading changes largely, but whether vehicle loading affects the engine emission re mains unclear yet. Using portable emissions measurement systems, Yao et al. (2012) measured that HC emission from full loaded HDDVs was 70% higher than that from half loaded ones. But the result of Huang et al. (2006) showed that the ratios between full loaded HDDVs and non loaded ones ranged 0.9–1.1. Figure 2d displays that the carbonyl emission of 50% loading and 100% loading were 105.2, 110.1 mg/km respectively. From our study, the influence of loading on diesel vehicles carbonyl emission was negli gible. But as diesel vehicles are generally overloaded in China and other developing countries, this factor needs further investigation.