Progress & Results
Progress at 24 project months (June 2011 - May 2013)
An evaluation of the dynamic and static preparation methods for traceable calibration gases for SO2 and NOx ambient air pollutants at concentrations close to the limit value has been completed. The evaluation has shown that the purity of the gases, including the dilution gas, is an important source of uncertainty. Meanwhile, a highly accurate portable system for the preparation of low concentration NO2 gas mixtures, based on permeation, is fully assembled, leak-proof and operational. This system has been validated for stability and robustness and it is currently being used as a transfer standard to demonstrate the comparability of NMIs’ calibration gas standards. Two other travelling standards, to demonstrate the comparability of NO and SO2 dynamic methods, have been characterised and validated. These standards are dynamic dilutors based on molbloc/molbox systems.
In this JRP particular emphasis is on the reactive contaminants in zero gas. Because zero gas (nitrogen or purified air) is used in analyser calibration, these impurities need to be minimized to (sub)-ppb level and their presence quantified by traceable measurements using optical systems, such as Cavity Ring Down Spectroscopy (CRDS). Once this measurement approach is fully traceable, a protocol for the certification of the impurity composition of zero gas will be made available. Major achievements have been made so far in this field. A comprehensive study of adsorption of ammonia at trace concentration levels (part-per-billion) on different tubing materials (coated and non-coated stainless steel and various polymers) has been completed. Further to this, for some low adsorbing polymers, differences in adsorption could be determined for the first time.
In addition, for the measurement of NO2 impurities in zero gas, an innovative and sensitive cavity-enhanced detection system has been constructed based on a high-power blue light emitting diode. The performance of this system has been compared to the ‘classical’ chemiluminescence detector for the trace level measurement range (part-per-billion) with good results.
In order to obtain zero gases, purifiers and zero gas generators are often used. The evaluation of a selection of commercial filter systems and zero gas generators is currently on-going. The aim is to demonstrate their efficiency in removing reactive contaminants that may interfere in the analysis of NOx and SO2.
The work related to indoor air pollution is focusing on a range of challenging (S)VOC that are typically emitted from building materials: hexadecane, dibutyl phthalate (DBP), dimethyl phthalate (DMP), 2-ethyl-1-hexanol, 1-methyl-2-pyrrolidone and styrene. The research activities on the generation of reference (S)VOC gas mixtures at low concentration levels have shown that for the very high boiling point compounds, such as dibutyl phthalate (bp 350 ̊C), this is a challenging objective because of condensation issues. Further investigation is needed to improve the methodology and to ensure traceability of these compounds. Meanwhile, the first tests on the production of a VOC constant emitting material have been carried out with promising results.
Research activities aiming at the development and validation of micro-sensors for air monitoring purposes are progressing beyond state of the art. Currently, two types of graphene sensors, based on epitaxial and exfoliated graphene, are available and they are under testing for the measurement of ambient levels of NO2. A laboratory validation of 11 selected micro sensors for the measurement of ozone has been performed based on a self-designed validation and calibration protocols. At this stage, the same validation procedure is being applied to NO2 sensors (graphene and commercially available sensors).
To date, ENV01 MACPoll has been presented at international conferences, to specific ISO and CEN standardisation committees involved in air quality and gas analysis, and to stakeholders. The project has over 30 examples of dissemination including papers, oral and poster presentations. An advisory board, made up of policy makers (European Commission), standardisation committees (CEN TC264, ISO TC158), air research institutes (NILU) and indoor air emission experts (AgBB) have been also set up. Further, collaboration agreements have been formalised with industrial collaborators, research organisations and air monitoring networks.