Transportation (road, rail, air and marine) released the largest proportion of Canada's NOX and CO emissions. Off-road vehicles were also an important source of NOX and CO emissions. The oil and gas industry was an important contributor to NOX emissions. Most of Canada's VOC emissions came from the oil and gas industry and from the use of paints and solvents. Agricultural activities were the main source of ammonia (NH3) emissions. Finally, open sources, largely activities associated with construction operations and dust from paved and unpaved roads, emitted most of the PM2.5 in Canada.