Dr. Neil Tindale, Texas A & M Univ. JGOFS/Arabian Sea Aerosols, short and long irradiation neutron activation analysis

JGOFS Arabian Sea Aerosol Data This mineral aerosol concentration data set is from samples collected during several cruises on the R/V Thomas Thompson during the JGOFS Arabian Sea field program. The data set includes the sampling period for each sample; the "Day of Year", yrday, number for the start of the sampling period for each sample; and the concentration of different elements for each sample, in micrograms per cubic meter. For the sampling period, "nd" is used as a filler to indicate "no data" gaps in the data array. The dust values are estimated using aluminum concentrations determined by neutron activation analysis. While most samples cover a multi-day period, we only have data for about 150 days. We didn't participate in all of the cruises and, on the cruises where samples were collected, often sampling conditions were less than ideal (bad weather, ship maneuvering, relative wind from astern etc.). A few samples that were collected showed obvious contamination from local sources, presumably from material from the R/V Thompson or from nearby fishing boats, and these samples were discarded and are not included in the data set. While the sampling period represents the period during which sampling occurred, sampling was usually not continuous. Sampling was frequently stopped, whenever sampling conditions were no longer suitable. Thus the concentration value at any particular date represents a time integrated sample which is usually non-continuous. Cautionary comments: 1. There may be a problem with the estimate for the mineral "dust" concentration. Most researchers use the average crustal ratio to estimate mineral dust concentrations using elemental concentration data (Al, Fe, etc.). Surface sand and silt samples that were collected in Oman in the Wahibah Sands region have distinct, non-crustal ratios. If individual aerosol samples are comprised of material from distinct sources, including Oman, then it is not unreasonable for their elemental ratios to differ from the published "average" crustal ratio that is used in most aerosol studies. 2. The amount of Ti in all the aerosol samples was small, despite there being a reasonable amount of dust material in most samples. The peaks for Cr and Ti overlap in the neutron activation short irradiation analysis and if significant quantities of Cr are present, this will interfere with the Ti analysis. With the exception of one sample, the Ti values are at or below the detection limit. The sole value above the detection limit was corrected for the Cr contribution using a correction based on the Cr values from the long irradiations. The correction changed the Ti value by less than 5%. The Ti data flagged as being at or below the detection limit was not corrected for possible Cr interference.