Friday, 25 September 2015

The VW debacle – does it matter?

At the heart of the VW debacle are official concerns about nitrogen oxide emissions from diesel engines and the consequent effects on human health. We may as well talk about nitrogen dioxide – NO2 as this gas is the primary health risk. Nitric oxide (NO) is also generated by diesel engines but is rapidly oxidised to NO2 by oxygen in the air. Nitrous oxide (N2O or laughing gas) is generated in smaller quantities via complex mechanisms which are not fully understood.

There is a long and detailed WHO review here and a UK Defra summary hereThe whole issue is exceedingly complex and it is not clear what health effects atmospheric NO2 may cause nor how permanent nor how severe long-term effects may be.

Annual mean concentrations in urban areas throughout the world are generally in the range of 20–90 μg/m3(15). In the European Community Respiratory Health Survey (ECRHS II) covering 21 European cities, annual ambient nitrogen dioxide concentrations ranged from 4.9 μg/m3 in Reykjavik to 72 μg/m3 in Turin (16). The maximum hourly mean value may be several times higher than the annual mean. For example, a range of 179–688 μg/m3 nitrogen dioxide has been reported inside a car in a road tunnel during the rush hour (15).

Nevertheless, if atmospheric NO2 can be reduced to a minimum it probably should be, but not at any cost and in any event it could take a lifetime to nail down what that minimum should be. This is one of the attractions of environmental science, the problems are interesting and likely to last for an entire career.

For example, the atmosphere in your home probably contains NO2, particularly if you have indoor combustion processes such as a gas stove or you live near a busy road or in a city. For all-electric homes domestic NO2 should depend on external levels and ventilation, but even here there are other factors.

For homes where there are combustion processes such as a gas stove, NO2 levels are extremely variable depending on external factors such as nearby roads and internal factors such as the type of gas stove, its ventilation and other sources of combustion. Move to the coast, rural Wales or rural Scotland if you really want to get away from NO2 - or Iceland.

Maximum levels associated with the use of gas appliances (gas cooking and heating) in European homes are in the range 180–2500 μg/m3.

So quite high levels. As for the effects:-

Several types of animal study have indicated that nitrogen dioxide increases susceptibility to respiratory infections (60,61,8890). An extensive set of data was collected using the infectivity model, which measures the total antibacterial defences of the lungs of mice. For long-term exposures, the lowest concentration tested that increased mortality when challenged with Klebsiella pneumoniae was 940 μg/m3 (0.5 ppm) for 3 months of exposure (91). After a 3-hour exposure, the lowest concentration tested that affected resistance to Streptococcus pneumoniae was 3760 μg/m3 (2 ppm) (92).

So domestic NO2 levels can easily be as high or higher than typical concentrations in the atmosphere outside even in cities. What effect did the actions of VW have on human health? I don’t know and neither does anyone else. Yet claims will be made and vast amounts of money will be transferred from one pocket to another because this is where we leave science behind.


Demetrius said...

Modern living in urban especially in urban areas and territories with extensive road and fuelling systems mean that a high proportion of us experience a great many chemical chemicals routinely 24/7. Just look around the average home and do a chemical count. It might explain why we are all going mad.

A K Haart said...

Demetrius - I think we are going mad because we are building our Tower of Babel.