Mass balance for lead in the California South Coast Air Basin: an update.

A mass balance for lead for the year 1989 in the South Coast Air Basin has inputs to the atmosphere of 600 +/- 190 kg/day and outputs of 580 +/- 160 kg/day, showing rough agreement. Stationary sources are responsible for only about 5% of the total lead emissions. The bulk of the lead is emitted from vehicles using leaded gasoline (37%) and unleaded gasoline (15%), as well as from resuspension of previously deposited lead on roads (43%). Over half of the total emitted lead deposits on roads and nearby soil, while about one-third is carried out the basin by wind. A small amount, less than 10%, is deposited on surfaces throughout the basin. These percentages are approximately the same as those in a mass balance for the same region calculated for 1972, when lead emissions from leaded gasoline were about a factor of 70 greater than leaded gas emissions in 1989. When the lead emissions are used as inputs to a simple continuously stirred flow reactor model for the basin, reasonable agreement is obtained between calculated and measured concentrations.