Thursday, 3 March 2011

The risk of cigarette smoke in cars

OK advance warning - this piece contains numbers. Right. First let's look at particulates - very, very fine particles of smoke in the air. They come mainly from vehicle exhausts and other cumbustion sources but in London, mainly from vehicle exhausts. If you're taking your kids to school in a car you're breathing air that contains relatively very high concentrations of particulates - the image below is average levels in an area of North London - the roads levels equal or exceed 32µg /m3. That's equal to 32000ng/m3. Don't get too worried yet - 32µg is 32/1000000ths (32 millionths) of a gram. The same as 32000 trbillionths of a gram. Where particulates are concentrated is the important thing - for high particulate concentrations indicate high BaP and PAH concentrations.

Right. Now PAH concentrations are the thing. PAHs are polycyclic aromatic hydrocarbons. PAHs are carcinogenic, and a subdivision of PAHs, BaPs, are particularly so. BaPs are benzo(a)pyrenes. Local councils monitor average levels of PAHs in the air in trbillionths of a gram per cubic metre or ng/m3.


The average level of PAHs in the air in Westminster in the orange PM10 areas are currently around 35 ng/m3. This is what you and your kids will be breathing in a car on these roads. Constantly. All the time. With every breath. 


Now cigarettes produce both smoke particles and PAHs. So how much worse off will you be with a smoker in the car? A report from the University of Minnesota Cancer centre says;
The presence of BaP and other carcinogenic PAHs in cigarette smoke is firmly established. Current levels of BaP are 1.5–15 ng per cigarette, whereas those of other established PAH carcinogens are collectively ≈3–50 ng per cigarette
Now of course the smoker inhales and absorbs a large proportion of that - let's say half. The volume of a car passenger compartment is about 3m3. So if a smoker in the car smoked an entire cigarette instantaneously, with no venting of the smoke and all of the smoke and vapour phase hanging in the air, it would result in a PAH level of 0.5 - 8 ng/m3  or about a maximum of about a quarter of the ambient level. With a window cranked open a fraction, and normal time taken to smoke a cigarette, the increase in PAH levels in the atmosphere inside the car is practically zero.


So go figure why the smoking Nazis (in this case the Lung Foundation and the RCP) are calling for a ban on smoking in cars.  

13 comments:

Henry Crun said...

"So go figure why the smoking Nazis (in this case the Lung Foundation and the RCP) are calling for a ban on smoking in cars"

Because, Raedwald, like all good Nazis, they are never happy unless they have someone to persecute.

Bill Quango MP said...

I agree with them. Smoking in cars is very hazardous to health.

I once flicked a butt that flew back in the rear passenger window and hit the mother in law.
As I turned to see what the fuss was, I almost ran down a squirrel.

If smoking was banned dangerous incidents like this wouldn't have happened for this particular reason, but would probably still happen for other reasons.

Now I think about it... Cup Holders should be banned. A large Starbucks tips over on a roundabout. No cup holders, no temptation to sit a super size espresso in it.
And radios. They must be bad. Think about all the deaths from shouting at the Today program and smashing into a tree.

In fact the common denominator seems to be cars. Or people.
Ban them both. Just to be sure.

Dick Puddlecote said...

Excellent post.

A far bigger worry than SHS in cars is why the majority of our population are too dense to work out such relative risks for themselves (and therefore discard idiotic pleading like that exhibited by the Lung Foundation).

It's a combination of bigotry and abject education at play, unfortunately.

Pat said...

Re Dick
The majority of the population can and do correctly, if approximately, assess these dangers for themselves. They just can't be arsed to argue with self serving idiots, and rely on poor enforcement of the stupid rules:- hence since I started driving in the 60's no-one complained of the 30mph limit, they just drove at 40

English Pensioner said...

Today I saw a couple of council workers sitting in the cab of their parked truck, feet on dashboard, happily smoking, which infringes rules about smoking in company vehicles (or is it only cars?).
I was very tempted to take a quick photo and e-mail the council, but really, in spite of the fact that I'm a non-smoker, I couldn't give a damn!

Anonymous said...

You seem to prove that smoking in the csr makes almost no effect. Yet why is it so easy to smell the smoke then?

Raedwald said...

Fair question, anon. Human smell can detect minute quantities of some things; in Vietnam, the NVA could smell the spearmint toothpaste that the US forces used at long distance, despite the actual molecules that would have been in the air being incredibly few. We can smell rotten eggs from very, very low concentrations of Hydrogen Sulphide (though paradoxically we can't smell high volumes of the gas - which is a shame, because it's actually extremely lethal).

Ed P said...

Your figures are confused. 1 microgram is 1000 billionths (nanograms), not 1000 trillionths of a gram. Also ng/m3 or ng.m-3, not ng/m-3
But the points about releative concentrations are well made!

Weekend Yachtsman said...

"So go figure why the smoking Nazis (in this case the Lung Foundation and the RCP) are calling for a ban on smoking in cars"

Because they can, and because anything that extends their power and reminds the citizens that they are just worms, is worth doing.

e-cigarettes said...

I was very tempted to take a quick photo and e-mail the council, but really, in spite of the fact that I'm a non-smoker, I couldn't give a damn

English Pensioner said...

My only reason was that the council are apparently intending to prosecute a local firm for permitting staff to smoke in company cars, when I consider they should have far better things to do. But complaining would waste even more of my money.

Don Cox said...

"since I started driving in the 60's no-one complained of the 30mph limit, they just drove at 40"

The point of a 30-mile limit is to make people drive at 40 or less. If the limit was set to 40, people would drive at 50.

Raedwald said...

Ed - many thanks; now corrected