Human activities have also dramatically altered the global nitrogen cycle via production of nitrogenous gases, associated with the global atmospheric nitrogen pollution. There are multiple sources of  atmospheric reactive nitrogen (Nr) fluxes. Agricultural sources of reactive nitrogen can produce atmospheric emission of ammonia (), nitrogen oxides () and nitrous oxide (). Combustion processes in energy production, transportation and industry can also result in the formation of new reactive nitrogen via the emission of , an unintentional waste product. When those reactive nitrogens are released to the lower atmosphere, they can induce the formation of smog, particulate matter and aerosols, all of which are major contributors to adverse health effects on human health from air pollution. In the atmosphere,  can be oxidized to nitric acid (), and it can further react with  to form ammonium nitrate (), which facilitates the formation of particulate nitrate. Moreover,  can react with other acid gases (sulfuric and hydrochloric acids) to form ammonium-containing particles, which are the precursors for the secondary organic aerosol particles in photochemical smog.