REAL-TIME, INSITU MEASUREMENTS OF ATMOSPHERIC OPTICAL-ABSORPTION IN THE VISIBLE VIA PHOTOACOUSTIC-SPECTROSCOPY .4. VISIBILITY DEGRADATION AND AEROSOL OPTICAL-PROPERTIES IN LOS-ANGELES

Aerosol light absorption (babs) has been measured in real-time in Los Angeles with a validated photoacoustic technique, and its impact on visibility degradation has been examined. These measurements were collected during ten days in the summer of 1987 for the Southern California Air Quality Study (SCAQS). Aerosol babs (λ = 514.5 nm) varied from an hourly average value of 7 × 10-6 m-1 in the 3-4 and 4-5 a.m. periods of 13 July to 9 × 10-5 m-1 in the 7-8 a.m. period of both 28 August and 3 September. This babs, which is due solely to elemental carbon (EC) showed a distinct diurnal pattern with low values at night, increasing around sunrise to higher values through mid-afternoon. Comparison of these data with aerosol light scattering data clearly illustrates that the contribution of aerosol light absorption to visibility degradation increases in importance under less polluted conditions. Other urban and rural studies show similar results. © 1990.