Air Quality Monitoring – BTEX Analyses
Benzene is a hydrocarbon that appears as a volatile liquid, capable of evaporating rapidly at room temperature; it is colourless and easily flammable and is the progenitor of a family of organic compounds defined as aromatic, due to the characteristic odour. Benzene is a natural component of oil (1-5% by volume) and its refining derivatives.
BTEX analysis gives a great indication of VOC emissions from an extended range of sources.
The primary man‐made sources of BTEX are via emissions from motor vehicles and aircraft exhaust, losses during petrol manufacturing, spills and cigarette smoke. BTEX are created and used during the processing of refined petroleum products and coal; during the production of chemical intermediates and consumer products such as paints and lacquers, thinners, rubber products, adhesives, inks, cosmetics and pharmaceutical products. BTEX compounds are among the most abundantly produced chemicals, with worldwide annual production of 8‐10 million tons of benzene, 5‐10 million tons of toluene, 5‐10 million tons of ethylbenzene and 10‐15 million tons of xylenes.
Benzene is easily absorbed by the human body almost exclusively by inhalation, while penetration through skin contact is negligible. It accumulates in tissues rich in fat (adipose tissue, bone marrow, blood and liver), where it is metabolised and then quickly eliminated in urine and exhaled air.
The carcinogenic capacity of benzene has been scientifically demonstrated and has been classified by the IARC (International Agency for Research on Cancer) in class 1 as a certain carcinogen for humans. In fact, its ability to cause acute and chronic leukaemia has been ascertained, at concentrations present in the past in work environments, with a risk proportional to the cumulative dose. The carcinogenic effect appears to be linked, as with other substances, to the action of intermediate metabolites that form in the body.
The European standard EN14662:2015 specifies a semi-continuous measurement method for determining the concentration of benzene present in ambient air based on automatic sampling and analysis by gas chromatography. The method describes the desired performance characteristics and establishes the minimum criteria required to select an appropriate automatic gas chromatograph (GC), by analysing the homologation tests. It also includes the assessment of the suitability of an analyser to be used in a given site in order to meet the data quality requirements as specified in Appendix I of Directive 20018/50/EC and the requirements during sampling, calibration, and the guarantee of quality of use.
The method is applicable to the determination of the mass concentration of benzene present in ambient air up to 50 μg/m3 (15.4 ppb) of benzene. This value represents the concentration level used for the approval test. Other concentration levels can be used, depending on the concentrations present in ambient air.
The PyxisGC BTEX instrument, according to EN14662:2015, monitors in real time the volatile organic compounds such as benzene, toluene, ethyl benzene and xylene.
The analysis cycle used lasts 15 minutes and the operation of the instrument can be divided into three different phases, which take place in parallel during the entire cycle:
Pre-concentration: the selective concentration of the reference compounds occurs through a silicon/glass MEMS device suitably filled with an adsorbent material. This phase lasts 10 minutes and takes place at temperatures below 50°C. A flow meter constantly samples the same volume of gas. Before the injection phase, the device heats up quickly above 100°C and the trapped material is desorbed and injected into the separation module
Gas chromatographic separation: the compounds desorbed during the injection phase arrive at the gas chromatographic column, also based on MEMS technology. Using ambient air filtered as gas carrier, the column separates the various compounds that elute with different times towards the final detection module.
Detection: the photo ionization detector (PID) quantifies the compounds leaving the column, based on the different retention times, creating the classic chromatographic graph. At the exit of the detector another flow meter is installed to monitor the correct functioning of the system.
PyxisGC BTEX is equipped with an internal memory, for data acquisition and chromatograms; it has a Cloud Software (Pollution Guardian) for the real-time monitoring and management of data acquired. Moreover, Guardian allows to remotely use the instrument.
PyxisGC BTEX analyses, thanks to the support of The Council for Research and Experimentation in Agriculture at the Puglia Regional Environmental Protection Agency (ARPA), were compared to another instrument for the BTEX monitoring; the test activities were carried out in the Puglia Arpa Air Quality Cabin located in Taranto, Via Alto Adige, Italy, and it is classified as a traffic station.
At the end of the parallel measurement and monitoring operations (for seven weeks), the data related to the Benzene analysed by both instruments installed in the ARPA Puglia C.R.A. control unit was compared.
Therefore, based on the average correlation data of 0.9065 (91%) it can be stated that the reported results prove the reliability of the PyxisGC BTEX and the accuracy of the obtained measurements.
Furthermore, the data shows that the PyxisGC BTEX perfectly follows the measurements taken with the Puglia ARPA control unit, although it has never been calibrated during the entire test period.