‘indicate that if the general public were during the day to 26 ug/m® at night, exposed to dust levels in excess of Cape Kumukahi the nephelometer measure- 1 mg/m, the public health problem from ment was 9, 2 ug/m>, the dust alone might be enormous, of data is available for Mauna Loa Observa- The At The greatest amount reasonableness of the upper limit value tory. of 1 mg/m* is also demonstrated by data 3 ug/m°*, and the nephelometer measure- which indicate that nonurban ambient air ments varied from 1.7 yug/ m®? at night to mass concentrations this high are usually, ‘ associated with conditions described as Here, the NASN measurement was 6.5 yg/m* during the day. Additional measurements made by the USAEC Health and Safety Laboratory {HASL) were dust storms!®?9, Measurements of ambient air mass 3 ug/m°, It is of interest in the present loading can be used to further define a context that Simpson7* made the following reasonable estimate for predictive pur- comment concerning the HASL measure- poses, ments: “The HASL filter samples contain The National Air Surveillance Network (NASN) has reported suchresults substantial dust (3-5 ug/ m°? of air sampled) for several years, because oi the fact that the filter was Data”? for 1966 show that there were 217 urban and 30 nonurban located less than one meter above the stations reporting, ground surface near areas with substantial The annual arithmetic average for the urban stations ranged personnel activity at the observatory site. " from 33 (St. Petersburg, Florida) to Thus, while this method of measurement 254 ue/m? (Steubenville, Ohio), witha may not have coincided with Simpson! s mean arithmetic average for all 217 interest, it does indicate that ambient stations of 102 ug/m>, air mass loadings may be very low on For the nonurban stations, the range was irom 9 (White sucn remote islands even when consider- Pine County, Nevada) to 79 ug/ m°> (Curry able human activity is occurring nearby. ’ County, Oregon), with a mean arithmetic On the basis of the above data, it average for all 30 stations of 38 ug/ m?>, would appear reasonable to use a value of No data in this report are available for 100 pe/m® as an average ambientair nonurban locations on small islands simi- mass loading for predictive purposes. lar to the Enewetak group; perhaps the Indications are that this value should be closest analog is the urban station at quite conservative for the Enewetak Honolulu, Hawaii, which had an annua! Islands, and therefore allows room for arithmetic average of 35 ug/m?, the uncertainty involved because the people More pertinent, but limited, data have recently been pubiisned for the island of Hawaii’ 1, 22 locations: Data are given for three Mauna Loa Observatory themselves may generate a significant fraction of the total aerosol. Therefore, they may be expusec to higher particulate concentrations than would be measured by located at a height of 3400 m, Cape a stationary sampler, Kumukahi, andthe city of Hilo, data for Hilo (for an unspecified period) Supporting evidence that 100 ug/m" is a reasonable value to use for predictive are given as 18 ug/m°>, and nephelometer purposes is provided by the National measurements varied from 18 ug; m? Ambient Air Quality Standards*°, NASN 114-25 Here