Vehicle Exhaust Particulates

The National Institute for Environmental Studies (NIES) announces the availability of NIES Certified Reference Material No. 8 "Vehicle Exhaust Particulates".

The prepared material contains about 80% of carbon, together with relatively low levels of Al, Ca and heavy metals.

Certified values are provided for Al, As, Ca, Cd, Co, Cr, Cu, K, Mg, Na, Ni, Pb, Sb, Sr, V and Zn, while reference values are reported for Ag, Br, Ce, Cs, Eu, La, Lu, Mo, P, Rb, Sc, Se, Sm and Th. The elemental composition of NIES Vehicle Exhaust Particulates is considered typical of automobile emission particulates.

The material for this reference material was collected from electrostatic precipitators in huge ventilators connected to a highway tunnel. The electrostatic precipitators were situated between cloth filters. Preliminary analysis demonstrated that little of the material caused from pavement.

About 7 kg of the material was used for the preparation of this reference material. Special care was taken when handling such a large amount of potentially hazardous material. Because the material readily produced a dust cloud and an irritating smell of gasoline, it was treated under wet condition as possible with special care concerning workers health and danger of explosion.

We examined the following three methods to produce homogeneous and easy-to-handle material. (1) We examined "Tablet Method" to bind the material under pressure, but we found difficulties in producing identical tablets and also contamination from the binders. (2) We examined "Sedimentation Granules Method" by suspending the material in a 35% ethanol solution. But in this case leaching of inorganic constituents from the material was significant. (3) We adopted "Paste-granules Method" by which we can get granulated material by drying after making a paste with 35% ethanol.

About 300 g of the material and 1 L of 35% ethanol were mixed well in a 10 L polyethylene container. After repeating this mixing procedure for the remaining material (7 kg), all mixtures were combined together in a large polyethylene tray, mixed again and air-dried for 2 weeks. The material was transferred to aluminum trays, dried in an air-oven at 60℃ for about 5 days and crushed into a fine powder in polyethylene bags with a wooden hammer. After passing through a 2-mm nylon screen, the powder was bottled into about 1,000 glass bottles.

At this stage, the prepared material was not homogeneous for certain elements, due mainly to deposition of water-soluble inorganic constituents onto the surface while drying. Therefore the material was re-mixed. All samples were combined together into a 30 L polyethylene bottle and mixed by rolling the bottle on a ball-mill apparatus for 2 hrs. The mixed powder was bottled again into about 1,000 glass bottles (7 g each).

A homogeneity test of the final product was performed by inductively coupled plasma emission and atomic absorption analyses following acid-dissolution of the samples. Six bottles were randomly selected from the lot of 1,000 bottles and 5 aliquots (about 300 mg) were taken from each bottle (total 30 samples).

The homogeneity of the "Vehicle Exhaust Particulates" was determined by using one-way analysis of variance. For the elements, Al, Ca, Cd, Co, Cr, Cu, K, Mg, Na, Ni, P, Pb, Sr and V, between-bottle variations were not significant. However, for Fe, Mn and Ti, between bottles variations were significant, though the reason for this has not been identified.

The certified values are based on results of determinations by at least three independent analytical techniques. The uncertainties of the certified values were estimated based on consideration of 2 times the standard deviation of the mean of the acceptable values, and of the 95% confidence intervals for the mean of individual methods.

Certified Values

Minor Constituent	Content*1 (wt. percent)	Method*2
Calcium	0.53±0.02	a,c,e
Aluminium	0.33±0.02	a,c,e,g
Sodium	0.192±0.008	a,b,c,e
Potassium	0.115±0.008	a,b,c,e
Zinc	0.104±0.005	a,c,d,e
Magnesium	0.101±0.005	a,c,e
Trace Constituent	Content*1 (μg/g)	Method*2
Lead	219±9	a,c,d
Strontium	89± 3	a,c,e
Copper	67±3	a,c,d,e
Chromium	25.5±1.5	a,c,e
Nickel	18.5±1.5	a,c,d,e
Vanadium	17±2	a,c,e,f
Antimony	6.0±0.4	a,c,e
Cobalt	3.3±0.3	a,c,e,f
Arsenic	2.6±0.2	a,c,e
Cadmium	1.1±0.1	a,c,d,e

Content*1

On an "as received" basis (see "Instruction for Use").

Method*2

a:	Atomic absorption spectrometry
b:	Flame emission spectrometry
c:	Inductively coupled plasma emission spectrometry
d:	Isotope dilution mass spectrometry, thermal ionization
e:	Instrumental neutron activation analysis
f:	Spectrophotometry
g:	Spectrofluorimetry

Reference Values

Element	Content*1 (μg/g)	Element	Content*1 (μg/g)
Phosphorus	510	Scandium	0.55
Bromine	56	Thorium	0.35
Molybdenum	6.4	Cesium	0.24
Rubidium	4.6	Silver	0.20
Cerium	3.1	Samarium	0.20
Selenium	1.3	Europium	0.05
Lanthanum	1.2	Lutetium	0.02

Content*1

On an "as received" basis (see "Instruction for Use").

Before sampling, mix the material well by vigorously shaking the bottle for about 1 min. Use a minimum sample weight of 300 mg for a single analysis. When a finer powder is required for analysis, transfer the content to an agate mortar and grind.

The material readily adheres to the wall of glass and Teflon vessels by electrostatic attraction and care should be taken in transfer operations.

Analytical results should be based on an "as received" basis without drying the sample. After usage, close the inner cap of the bottle tightly and keep it in a silica-gel desiccator.

This reference material contains siliceous material. The certified and reference values are based on analyses performed on the entire sample. Therefore, decomposition procedures should be designed to achieve complete dissolution of the material such as by the use a mixture of nitric/perchloric/hydrofluoric acids.

In our experience it was necessary to heat the sample at around 200℃ in the presence of perchloric acid to dissolve the material completely. Hydrofluoric acid was also added after the digestate became a clear yellow color.