THERMAL ANALYSES OF THE LOS ANGELES SMOG AEROSOL

Abstract

IT HAS BEEN SHOWN BY EARLIER STUDIES ON THE FORMATION OF THE LOS ANGELES SMOG AEROSOL, THAT A SIGNIFICANT FRACTION OF THE PARTICULATE MATTER IN THE VISIBLE SIZE RANGE IS MADE BY SECONDARY GAS-PARTICLE CONVERSION PROCESSES, AND THAT IT CONSISTS MAINLY OF LIQUID MATTER.IN THIS STUDY THE VOLATILITY WAS STUDIED QUANTITATIVELY BY HEATING THE SMOG AEROSOL UP TO 250/SUP O/C AND SIMULTANEOUSLY MEASURING THE SCATTERING COEFFIFICIENT USING A NEPHELOMETER AND THE CHANGE OF SIZE DISTRIBUTION BY AN OPTICAL COUNTER.THE THERMAL ANALYSES REVEALED THAT 50-80PERCENT OF THE SUBMICRON AEROSOL MASS IS VOLATILE AT 220/SUP O/C.INSPECTION OF THE SHAPES OF THERMO-NEPHELOGRAMS (BSCAT VS TEMPERATURE) ALSO REVEALED THAT PHOTOCHEMICALLY FORMED AEROSOLS HAVE DISTINCTLY DIFFERENT THERMO-NEPHELOGRAMS THAN THOSE OBTAINED ON HUMID 'HAZY' DAYS.THUS IT IS SUGGESTED THAT THERMAL ANALYSES MAY AT LEAST IN SOME INSTANCES PROVIDE THE MEANS OF ON-LINE MONITORING THE ORIGIN OF THE AMBIENT AEROSOL.(A.)