Gasoline worse than diesel when it comes to some types of air pollution: secondary organic aerosols SOAs

SOAs are tiny particles that are formed in air and make up typically 40 percent to 60 percent of the aerosol mass in urban environments. Fine-particle pollution can cause human health effects, such as heart or respiratory problems

While diesel engines emit pollutants such as soot and nitrogen oxides, for organic aerosol pollution they account for less than 20 percent - that being accounted for by emissions from petrol engines.