Environmental Analysis Facility

Teflon-membrane filters are used for the measurement of mass and elemental concentrations. 

Quartz-fiber filters are used for the determination of carbon fractions and inorganic ions in the particulate phase.

Cellulose-fiber filters with impregnated solution are used to capture gaseous pollutants such as nitric acid (HNO₃), sulfur dioxide (SO₂), and ammonia (NH₃).

Polycarbonate filters are used for particle morphology analysis using optical and electron microscopy.

Coated Teflon deposition films are used to collect particle deposition on a sticky coating to determine deposition fluxes.

Water sampling vials are used for precipitation, wastewater, stormwater, surface water, and ground water sampling.  Sample batches are conditioned and acceptance tested prior to sampling to ensure low background levels.

EAF’s filter preparation, chain-of-custody, conditioning, and gravimetric analysis follows the U.S. EPA’s reference method requirements for PM analysis (Appendices J and L to Part 50, Code of Federal Regulations) and EPA’s Quality Assurance Guidance Document.

Unexposed and exposed samples are equilibrated at temperature (21.5 ± 1.5 °C) and relative humidity (35 ± 5%) controlled environment for a minimum of 48 hours prior to weighing. Weighing is performed on microbalance with ±0.001 mg sensitivity. 

Electrostatic charges on each sample that can bias weights are neutralized by exposure to a ²¹⁰Po ionizing source for 60 seconds prior to placing filter on a balance pan in a weighing chamber. The microbalance is calibrated with 500, 200, 100 and 50 mg Class 1 standard weights. After every 10 samples are weighed, the 200 mg calibration and tare are re-checked. If the results of these performance tests deviate from specifications by more than ±0.003 mg, the balance is re-calibrated. 

Replicate pre-sampling (initial) and post-sampling (final) weights must be within ± 0.010 mg and ± 0.015 mg of the original weights, respectively. Pre- and post- weights, check weights, and re-weights (if required) are recorded on data sheets, as well as being directly entered into a database via an internet connection.

Sample Extraction

Water-soluble anions (e.g., chloride, nitrite, nitrate, and sulfate), and cations (e.g., ammonium, water-soluble sodium, magnesium, potassium, and calcium) are obtained by extracting non-liquid samples in deionized-distilled water (DDW). The extraction vials are capped, sonicated, shaken, and aged overnight to ensure complete extraction.

Acid Digestion

Samples are digested using a hot block acid digestion. The acid digestion solution (e.g., a mixture of nitric acid and hydrochloric acid) follows U.S. EPA methods or are specified by project sponsors.

Aqueous Solution Samples

Precipitation, water, and other aqueous samples are centrifuged or filtered to remove solids prior to chemical analysis of metals and ions in the same manner as the filter extracts.

XRF analyses is typically performed on Teflon‑membrane filters and compressed soil pellets with a PANalytical Epsilon 5 EDXRF analyzer using a side‑window, liquid‑cooled, 100 KeV, 24 milliamp dual anode (Sc/W) x‑ray tube and secondary targets, for the following 51 elements (i.e., Na, Mg, Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Sb, Ba, La, Ce, Sm, Eu, Tb, Hf, Ta, W, Ir, Au, Hg, Tl, Pb, and U).  An Epsilon 4 that uses an Ag anode tube with direct or filtered excitation is also available. 

In XRF, inner shell electrons are removed from the atoms of the aerosol deposit. An x‑ray photon with a wavelength characteristic of each element is emitted when an outer shell electron occupies the vacant inner shell. The number of these photons is proportional to the number of atoms present. The characteristic x‑ray peaks for each element are defined by 200 eV‑wide windows in an energy spectrum ranging from 1 to 80 KeV. The EDXRF system is calibrated using thin film multielement standards.

Acid-digested and filtered aqueous samples are is submitted for ICP-MS analysis of 70 elements (including those of the 51 listed for XRF, beryllium, rare-earth elements, and isotopes).  Lead, strontium, and other isotopes are useful for attributing pollutants to their sources.  Analyses are performed with Perkin Elmer Model NexION 300D and 2000 ICP-MS analyzers. Minimum detection limits for ICP-MS analysis are low in the range of 0.001-0.01 μg/filter.

Water-soluble anions (e.g., fluoride, chloride, nitrite, nitrate, sulfate, bromide, and phosphate); cations (e.g., ammonium, water-soluble sodium, magnesium, potassium, and calcium); carbohydrates (e.g., levoglucosan, arabitol, and mannitol); and organic acids (e.g., formate, acetate, and succinate) are measured with Thermo Scientific Dionex Model ICS-6000 and ICS-5000⁺ ion chromatograph (IC) with conductive detector, pulsed amperometric detector, or electrochemical detector. In IC, an ion‑exchange column separates the sample ions in time for individual quantification. The column effluent enters a suppressor column, where the chemical composition of the component is altered, resulting in a matrix of low conductivity. The ions are identified by their elution/retention times and are quantified by the peak area.

 Calibration standards are prepared by diluting the primary standard solution to concentrations covering the range of concentrations expected in the filter extracts. After analysis, each individual chromatogram is reviewed for: 1) proper operational settings, 2) correct peak shapes and integration windows, 3) peak overlaps, 4) correct background subtraction, and 5) quality control sample comparisons.

Organic carbon (OC), brown carbon (BrC), elemental carbon (EC), black carbon (BC), and carbonate carbon are acquired by DRI Model 2015 multiwavelength  thermal/optical carbon analyzer. The TOR/TOT method is based on the principle that carbon-containing particles are converted to gases under different temperature and oxidation conditions. The analyzer is programmed to accommodate different analytical thermal protocols (e.g., IMPROVE_A and NIOSH5040). The IMPROVE_A protocol has been implemented in long-term U.S. networks. It separates carbon into four OC fractions (OC1 to OC4 at 140, 280, 480, and 580 ºC in a helium atmosphere), three EC fractions (EC1 to EC3 at 580, 740, and 840 ºC in a helium/oxygen atmosphere), and an optical pyrolysis (OP) fraction. The total carbon (TC) is the sum of OC and EC, where OC= OC1+OC2+OC3+OC4+OP and EC=EC1+EC2+EC3-OP.

Since 2016, laser reflectance and transmittance have been measured at multi- wavelengths (i.e., 405 nm, 445 nm, 532 nm, 635 nm, 780 nm, 808 nm, and 980 nm), that allow the determination of BrC and have been used for source apportionment studies.