Sources for h2so4 and hno3 in the air Both substances are formed in the air Precursor to H2S04: S02 Precursor to hno3 No2 Concentrations of the precursors so2 and NO2 are greatly increased by man-made activities, especially fossil fuel combustionSources for H2SO4 and HNO3 in the air • Both substances are formed in the air – Precursor to H2SO4: SO2 – Precursor to HNO3: NO2 • Concentrations of the precursors SO2 and NO2 are greatly increased by man-made activities, especially fossil fuel combustion