Aerosol formation in the photooxidation of isoprene and β-pinene

Isoprene and β-pinene, at concentration levels ranging from a few ppb to a few ppm, were reacted photochemically with NOₓ in the Caltech outdoor smog chamber facility. Aerosol formation from the isoprene photooxidation is found to be negligible even under extreme ambient conditions due to the relatively high vapor pressure of its products. Aerosol carbon yield from the β-pinene photooxidation is as high as 8% and depends strongly on the initial HC/NOₓ ratio. The average vapor pressure of the β-pinene aerosol is estimated to be 37 ± 24 ppt at 31 °C. Monoterpene photooxidation can be a significant source of secondary aerosol in rural environments and in urban areas with extended natural vegetation.