Theresa Fall

Chemical Characteristics of PM10 Aerosols Collected in the Los Angeles Area

A PM_(10) monitoring network was established throughout the South Coast Air Basin (SOCAB) in the greater Los Angeles region during the calendar year 1986. Annual average PM_(10) mass concentrations within the Los Angeles metropolitan area ranged from 47.0 µg m^(-3) along the coast to 87.4 µg m^(-3) at Rubldoux, the furthest inland monitoring station. Measurements made at San Nicolas Island suggest that regional background aerosol contributes between 28 to 44 percent of the PM_(10) aerosol at monitoring sites In the SOCAB over the long term average. Five major aerosol components (carbonaceous material, NO- _3, SO=_4, NH+_4, and soil-related material) account for greater than 80 percent of the annual average PM_(10) mass at all on-land monitoring stations. Peak 24-h average mass concentrations of nearly 300 µg m^(-3) were observed at inland locations, with lower peak values (˜130–150 µg m^(-3)) measured along the coast. Peak-day aerosol composition was characterized by increased NO-_3 Ion and associated ammonium ion levels, as compared to the annual average. There appears to be only a weak dependence of PM_(10) mass concentration on season of the year. This lack of a pronounced seasonal dependence results from the complex and contradictory seasonal variations in the major chemical components (carbonaceous material, nitrate, sulfate, ammonium ion and crustal material). At most sites within the Los Angeles metropolitan area, PM_(10) mass concentrations exceeded both the annual and 24-h average federal and state of California PM_(10) regulatory standards.

Hydrochloric acid: A regional perspective on concentrations and formation in the atmosphere of Southern California

Atmospheric gaseous hydrochloric acid (HCl) concentrations and water-soluble species in the aerosol phase were measured at nine sites in Southern California throughout the year 1986. Annual average HCl concentrations measured by the denuder difference method ranged from 0.39 ppb at an offshore island to 1.25 ppb onshore at Hawthorne, California. An ion balance on the aerosol shows that coarse particle chloride begins as sea salt over the ocean and is depleted relative to aerosol sodium with transport inland. Total chloride and sodium balances show that chloride depletion from the aerosol is matched by a comparable increase in gaseous HCl concentrations, consistent with the proposition that acid gas reactions with sea salt are the principal source of gaseous HCl in the Southern California atmosphere. Fine aerosol chloride exceeds fine particle sodium on a number of occasions, particularly at one inland site known for extraordinarily high NH_3 levels. There is evidence that coarse aerosol chloride from sea salt is being processed by atmospheric reactions through HCl to form fine aerosol, possibly NH_4Cl.

Characteristics of airborne particles inside southern California museums

The concentrations and chemical composition of suspended particulate matter were measured in both the fine and total size modes inside and outside five southern California museums over summer and winter periods. The seasonally averaged indoor/outdoor ratios for particulate matter mass concentrations ranged from 0.16 to 0.96 for fine particles and from 0.06 to 0.53 for coarse particles, with the lower values observed for buildings with sophisticated ventilation systems which include filters for particulate matter removal. Museums with deliberate particle filtration systems showed indoor fine particle concentrations generally averaging less than 10 μg m^(−3). One museum with no environmental control system showed indoor fine particle concentrations averaging nearly 60 μg m^(−3) in winter and coarse particle concentrations in the 30–40 μg m^(−3) range. Analyses of indoor vs outdoor concentrations of major chemical species indicated that indoor sources of organic matter may exist at all sites, but that none of the other measured species appear to have major indoor sources at the museums studied. Significant fractions of the dark-colored fine elemental (black) carbon and soil dust particles present in outdoor air are able to penetrate to the indoor atmosphere of the museums studied, and may constitute a soiling hazard to works of art displayed in museums.

BASINWIDE NITRIC ACID AND RELATED SPECIES CONCENTRATIONS OBSERVED DURING THE CLAREMONT NITROGEN SPECIES COMPARISON STUDY

In conjunction with the Claremont Nitrogen Species Comparison Study, tandem filter units designed to collect HNO_3/total aerosol (TA) NO_3− and NH_3/TA NH+_4 were operated at seven locations throughout the Los Angeles area, including Claremont. The sampling methods used were related to the comparison study via intensive short-term and long-term measurements made at Claremont by both the tandem filter method and the denuder difference method. Between methods, 4-h and 6-h duration HNO_3 samples taken by the tandem filter method were higher (~ 20%) than the HNO_3 results obtained by the denuder difference method. As sampling duration increased to 22 h, the tandem filter method HNO_3 and NH_3 concentration measurements increased, while the 22-h denuder difference method HNO_3 values remained indistinguishable from the average of simultaneous short-term 4- and 6-h average samples. Analysis of the basinwide data showed that Claremont experienced the highest measured HNO_3 concentrations in the Los Angeles area during the period of the comparison study, confirming that Claremont was a wise choice for the main site of the study. In contrast, an alternative site near Riverside experienced the lowest HNO_3 levels in the air basin, accompanied by high aerosol nitrate and very high NH_3 concentrations.

Response to Comment on “Hydrofluoric Acid in the Southern California Atmosphere”

Dr. Dasgupta writes to ask for additional details regarding the chemical analysis of fluoride collected on potassium hydroxide impregnated filters (1). We are pleased to reply.