Abstract:
In this study, the chemical constituents of the airborne fine particulate matter (those finer than 2.5 micrometer) emitted from a seawater tank covered with crude oil (MC252 surrogate) slick of 0.5 mm, before and after mixing with dispersant (Corexit 9500A, dispersant to oil ratios of 1:25 and 1:100) was determined. Aerosol generation was facilitated through the bursting of air bubbles injected at a controlled diameter of 0.6 mm into a vertical seawater column. PM2.5 particles were also size-fractioned into 13 size bins covering <60 nm to 12.1 µm on 81-mm filters using a low-pressure cascade impactor. Chemical analysis was conducted through the development of a gas chromatography-mass spectrometry (GC/MS) technique to efficiently extract organic compounds from quartz filters using n-pentane solvent.
Suggested Citation:
Nima Afshar-Mohajer; Kirsten Koehler; Ana Rule. 2020. Chemical analysis of airborne fine particulate matter emitted from different types of crude oil slick due to bubble bursting. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-rte4-s004
Data Parameters and Units:
Dataset consists of 5 Excel files which are “Chemical analysis (dodecane & BMEP)”, “Converting dodecane and BMEP to crude oil and dispersant”, “Development of the calibration curves”, “Gravitational analysis of PM2.5”, and “Particle size distribution data”.
The file “Chemical analysis (dodecane & BMEP)” includes results of GC/MS analyses and filter extraction efficiencies. It shows that how the mass extracted from the filter of each case and also the estimated concentration of dodecane or BMEP from the headspace of the tank for each experimental case were made. There were 4 experimental cases: a) the case of clean seawater with no oil slick, b) the case of seawater with a 0.5-mm-slick of pure crude oil, c) the case seawater with a 0.5-mm slick of crude oil mixed with dispersant at the ratio of 100 to 1 (DOR 1:100), d) the case of seawater with a 0.5-mm slick of crude oil mixed with dispersant at the ratio of 25 to 1 (DOR 1:25). In all cases, aerosol droplets were produced through a burst of bubbles on the water surface. There are 3 main headers in this file that are “Amounts on Quartz. Reading w Rtx-VMS column”, “Constant properties”, and “Estimated parameters”. The headers “Samples (samples containing Dodecane)”, “Peak area of Dodecane crude oil marker are subdivisions of the header “Amounts on Quartz. Reading w Rtx-VMS column” while V_Solvent (L), Sampling time (min), and Average sampling flow rate (L/min) are subdivisions of“Constant properties”. “ρ_Dodecane (ug/L)”, “ƞ_Dodecane”, and “C_Dodecane (ng/m3)” are subdivisions of Estimated parameters”.
The file “Converting dodecane and BMEP to crude oil and dispersant” shows how the estimated dodecane and BMEP concentration by the file of Chemical analysis (dodecane & BMEP) can be translated into crude oil and dispersant concentrations in the air. It includes - Sample name, Concentration (ug/mL), and Peak Area. Other headers are-Calculated concentration (ug/mL) Weight = Equal, Calculated concentration (g/mL) Weight = Equal, Percent per sample
The file “Development of the calibration curves” describes quality control and quality assurance calibration plots that should be provided in all GC/MS analyses to know how the peak number values by the GC/MS can be associated with the concentration of what being detected. It includes - Sample name, Concentration (ug/mL), and Peak Area. These headers are for the establishment of a calibration curve. Other headers are regarding samples whose quantities of dodecane are to be determined are sample and peak area. The peak area is the measurement captured on quartz (Reading w Rtx-VMS column).
The file “Gravitational analysis of PM2.5” contains the direct measurement of the mass concentrations of the airborne particulate matter with an aerodynamic diameter finer than 2.5 microns for each above-mentioned case of our experiments. The measurements were made possible using a microbalance and we read the data from the machine display and recorded in the file, and includes - case (type of material analyzed- Seawater only, Crude oil only, DOR 1:25, and DOR 1:100), Rep. 1 (ug/m3), Rep. 2 (ug/m3), Rep. 3 (ug/m3), and Ave (ug/m3). Rep. is short for replicate. Ave is average. DOR 1:25 and DOR 1:100 are slicks of crude oil-dispersant mixtures.
The file “Particle size distribution data” includes the total mass concentration and size distribution of the airborne particulate matter finer than 380 nm measured using a scanning mobility particle sizer instrument. It includes - mid-point dp (nm), The case of DOR 1:25 (#/cm3), The case of DOR 1:100 (#/cm3), The case of crude oil (#/cm3), and The case of seawater only (#/cm3). Note that DOR 1:25 and DOR 1:100 are slicks of crude oil-dispersant mixtures.
Please note - BMEP is the short form of 1-(-2butoxy-1-methylethoxy)-2-propanol, which is the marker that was used for Corexit 9500; Dodecane is the marker for crude oil. SIMf is an internal naming code used by the technician who performed the gas chromatography and mass spectrometry (GC/MS) analyses; Blank in the filter names denotes that filter has been a baseline filter that was not obtained from the experiment; Ch in the names denotes the filter that was assigned for chemical analysis. The dates at the end of the names denote the date that the technician analyzed the sample; M_CF refers to either dodecane or BMEP mass derived from a filter contaminated by a spiked droplet of crude oil- or dispersant-pentane; M_BF refers to either dodecane or BMEP derived from a blank filter; M_P refers to either dodecane or BMEP directly injection of the same amount of crude oil or dispersant. Finally, eta (Greek letter) refers to the extraction efficiency of the filter.
Methods:
The laboratory setup consisted of a vertical tank filled with seawater, 31.5 L airspace for aerosol sampling, and a bubble generating nozzle in the bottom that aerosolized the oily droplets after burst of bubbles. Four different cases were studied: no slick, 0.5-mm-thick slick of pure crude oil (MC252 surrogate), dispersant (Corexit 9500A) mixed with crude oil at dispersant to oil ratio (DOR) of 1:25, and DOR of 1:100. The resulting airborne droplets were sampled using proper aerosol samplers.
Instruments:
Application of a personal micro-environmental aerosol speciation sampler (PMASS) onto 25-mm filters for gravimetric and chemical analyses of PM2.5, and a gas chromatography and mass spectrometry (GC/MS) technique to efficiently extract organic compounds from quartz filters using n-pentane solvent. A scanning mobility particle sizer instrument was also used for real-time monitoring of the total concentration and size distribution of the particles finer than about 380 nm.
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