Defra’s Air Quality Expert Group (AQEG) published two new reports today (20/12/21):
Exhaust Emissions from Road Transport (link); and
Ozone in the UK – Recent Trends and Future Projections (link).
AQC’s Ben Marner was part of the team which prepared both reports.
The report on exhaust emissions provides a thorough review of the key current and emerging issues regarding exhaust emissions from road traffic. It accompanies previous work on non-exhaust emissions. It highlights recent trends and approaches to air quality modelling. The report on ground level ozone explains that average ozone concentrations have been increasing in recent years, but that peak values have remained fairly constant. The involvement of AQC staff in producing both of these AQEG reports makes the Company ideally placed to consider the implications of this evidence for its clients.
Exhaust Emissions
The report on exhaust emissions provides a thorough review of the key current and emerging issues regarding exhaust emissions from road traffic. It accompanies previous work on non-exhaust emissions. The report explains that exhaust emissions from modern vehicles are now often driven by the behaviour of emissions control systems rather than the engines themselves. For pollutants such as NOx, which are released directly during combustion, the variable performance of emissions control systems has increased the spread between high- and low-emissions periods which occur during typical driving. The latest, and emerging, type approval regulations will help address this but, at present, there is significant potential for isolated emissions events and thus local pollution hotspots. This is despite the well-reported reductions in average NOx emissions and concentrations.
Emissions control systems also emit pollutants which are not released directly from the engine. This is the source of traffic-related ammonia, which AQC has been instrumental in quantifying and raising awareness of. The latest AQEG report summarises current evidence on this and shows good agreement between emissions derived from AQC’s ambient roadside measurements and those from remote sensing.
The AQEG report also summarises the state of evidence on modelling traffic-related air pollution. Because AQC staff helped to prepare both the AQEG report, and many of the studies which it cites, the Company is ideally placed to ensure that air quality modelling carried out for its clients is fully aligned with this seminal report from AQEG on behalf of Defra.
Ozone
The AQEG report on ground level ozone expands and updates an earlier 2009 AQEG report on this subject, in which AQC’s Tim Williamson was involved. Because ground level ozone is principally a secondary pollutant, it often gets overlooked in the context of air quality impact assessments. It is, though, very important in its effects on both human health and vegetation, and also in driving chemical reactions with other pollutants. Impacts of NOx often need to be understood in the context of available ozone, for example, guidance from the IAQM on the critical level for 24-hour NOx is predicated on assumptions regarding current ozone concentrations. This latest AQEG report explains that average ozone concentrations have been increasing in recent years, but that peak values have remained fairly constant. Future projections are uncertain but increases to both urban and rural ozone concentrations seem likely in the immediate future. The involvement of AQC staff in producing this AQEG report makes the Company well placed to consider its implications in assessment work for its clients.
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