Spatial and temporal distribution of atmospheric nitric acid and particulate nitrate concentrations in the Los Angeles area

Abstract

A 1-year atmospheric measurement program was conducted
\nthroughout the South Coast Air Basin in the
\ngreater Los Angeles area during 1986 to determine the
\nlong-term average concentration patterns of gaseous HNO_3,
\nand aerosol nitrates. Upwind of the air basin at San Nicolas
\nIsland, HNO_3, levels are very low, averaging 0.3 µg m^(-3) (0.1 ppb) over the year 1986. Annual average HNO_3
\nconcentrations ranged from 3.1 µg m^(-3) (1.2 ppb) near the
\nSouthern California coast to 6.9 µg m^(-3) (2.7 ppb) at an
\ninland site in the San Gabriel Mountains. At most monitoring
\nstations, a majority of the inorganic nitrate (HNO_3 plus its reaction product, aerosol nitrate) was in the aerosol
\nphase. Conversion of HNO_3 to aerosol nitrates was most
\npronounced at Rubidoux, near Riverside, CA, where on the
\naverage 94% of the inorganic nitrate was found in the
\naerosol phase, and where fine particle nitrate concentrations exceeded 109 pg µg^(-3), during the peak 24-h period examined.