▁Part icles ▁in ▁the ▁atmosphere ▁can ▁be ▁divided ▁into ▁two ▁types , ▁depending ▁on ▁the ▁way ▁they ▁are ▁em itted . ▁Primary ▁particles , ▁such ▁as ▁min eral ▁dust , ▁are ▁em itted ▁into ▁the ▁atmosphere . ▁Second ary ▁particles , ▁such ▁as ▁am mon ium ▁nit rate , ▁are ▁formed ▁in ▁the ▁atmosphere ▁through ▁gas - to - part icle ▁conversion . ▁ ▁S ources ▁ ▁Some ▁particul ates ▁occur ▁naturally , ▁origin ating ▁from ▁vol cano es , ▁dust ▁storm s , ▁forest ▁and ▁grass land ▁fires , ▁living ▁veget ation ▁and ▁sea ▁sp ray . ▁Human ▁activities , ▁such ▁as ▁the ▁burning ▁of ▁foss il ▁fu els ▁in ▁vehicles , ▁stub ble ▁burning , ▁power ▁plants , ▁road ▁dust , ▁wet ▁cool ing ▁to wers ▁in ▁cool ing ▁systems ▁and ▁various ▁industrial ▁processes , ▁also ▁generate ▁significant ▁amounts ▁of ▁particul ates . ▁Co al ▁comb ust ion ▁in ▁developing ▁countries ▁is ▁the ▁primary ▁method ▁for ▁he ating ▁homes ▁and ▁supp lying ▁energy . ▁Because ▁salt ▁sp ray ▁over ▁the ▁o ce ans ▁is ▁the ▁over wh el ming ly ▁most ▁common ▁form ▁of ▁partic ulate ▁in ▁the ▁atmosphere , ▁anth rop ogen ic ▁a eros ols — th ose ▁made ▁by ▁human ▁activities — current ly ▁account ▁for ▁about ▁ 1 0 ▁percent ▁of ▁the ▁total ▁mass ▁of ▁a eros ols ▁in ▁our ▁atmosphere . ▁ ▁Marine ▁de br is ▁Marine ▁de br is ▁and ▁marine ▁a eros ols ▁refer ▁to ▁particul ates ▁susp ended ▁in ▁a ▁liquid , ▁usually