Woodheater-Car Comparison

Many people think that cars are the worst pollutants.  Sydney has lots of cars but few woodheaters, so we’d expect all the passenger cars in Sydney to produce more total pollution than the small number of woodheaters.  PM2.5 are now considered the most health-hazardous air pollutant, responsible for about 10 to 20 times as many premature deaths as the next worst pollutant, ozone.


New cars must satisfy strict Euro 5/6 pollution standards, which require a new car, 4WD or SUV travelling 20,000 km to year to emit less than 0.1 kg of PM2.5.  In contrast, the NSW EPA estimates that a new wood heater will emit 9.8 kg of health-hazardous PM.25 per year.  Thus a brand new AS4013 heater emits as many PM2.5 in 10 hours as a new car does in an entire year and a heater burning 2 tonnes of firewood will emit 19.6 kg of PM2.5, as much as 196 passenger cars!

 

 A total of 4503 tonnes of PM2.5 per year in Sydney are emitted by Sydney’s woodheaters, compared to a total of 797 tonnes for all passenger cars.  In other words, the average woodheater emits 96 times as much PM2.5 pollutiion as the average passenger car. 

Sydney has lots of cars. Armidale has lots of woodheaters.  The graph below compares monthly average PM2.5 nephelometer measurements, recorded by the NSW EPA in Armidale in 1996 and Sydney in 1999.  When woodheaters are not in use, Armidale ha
Air toxics NEPM Pollutants
s cleaner air.  But as soon as the woodheating season starts, Armidale's pollution rises dramatically, with only a small rise in Sydney where only 4.3% of households use wood as the main form of heating.  This again shows that the average woodheater emits a lot more health-hazardous PM2.5 pollution than the average car and that the only way for Armidale to have wintertime air that is as clean and healthy as in Sydney is for residents to use non-polluting heating.


 Prof John Todd’s article in “Clean Air and Environmental Quality” notes that there has been “only marginal improvement over the past 15 years” in woodheater emissions.  Emissions from new cars have also improved.  A new car driving 15,000 km per year emits about 150 g of PM2.5.  With average fuel consumption of 2 tonnes per year (Sydney) or 4 tonnes (Armidale), a new woodheater will emit 133 times (Sydney) or 267 times (Armidale) as much health-hazardous PM2.5 pollution as the average new car driving 15,000 km per year. 

 
Woodheaters also emit more greenhouse gases than other forms of heating.  Many councils offer subsidies to replace woodheaters with non-polluting heating.  Woodheater owners who are concerned about their health or the environment should remember the advice of the NSW DECC “If you can see or smell smoke from your wood heater then you are causing a problem for yourself, your family and your neighbors and consider taking up this offer.

Proportion of PM2.5 emissions (the most health-hazardous air pollutant) emitted by residential wood heaters (purple line joining the triangles) in Sydney by month.  This graph from NSW EPA website, is from their emissions inventory which shows that more than half of all man-made PM2.5 emissions are from the small proportion of households using wood heaters.  ABS statistics show that only 5% of Sydney households use wood as the main form of heating.

 

 

   The table below compares all major pollutants and air toxics emitted by the average petrol-fuelled passenger car and the average woodheater, according to the NSW EPA Emissions Inventories for 2008 and 2003. 

   Exhaust emissions from petrol-fuelled passenger cars in Syndey have fallen from 797 tonnes PM2.5 per year, to 88 tonnes,  with substantial reductions in all major pollutants.  In contrast, wood heater emissions have increased from 4503 tonnes to 7359 tonnes, almost 10 times more than all the petrol-fuelled passenger cars in Sydney. 

   This is despite the fact ABS estimates show a decline in the proportion of households using wood as the main form of heating in NSW (from 11.8% 2002 to 10.3% in 2008). 

   Because of the big reduction in emissions per vehicle (from 0.44 kg per year to 0.05 kg), a heavily used wood heater in Sydney can emit over 1,000 times as much PM2.5 (the most health-hazardous pollutant) as the average petrol-fuelled passenger far.  In general, woodheaters emit more toxic pollutants – about 44 times as many PAH as the average car, 12 times as much benzene and other VOC (volatile organic compounds) and 66 times as much formaldehyde.


Comparison of air pollution emissions from woodheaters and petrol-fuelled passenger cars in Sydney in 2008  and 2003


2008 Emissions - Sydney

Cars

Woodheaters

Ratio

Ambient AQ NEPM

t/yr

kg/vehicle

t/yr

kg/heater

woodheater/car

  PM2.5

88

0.05

5457

51.43

1059.66

  VOC (ozone precursor)

7789

4.30

5952

56.10

13.04

  CO

75067

41.45

40034

377.32

9.10

  NOX

21575

11.91

601

5.66

0.48

  SO2

144

0.08

96

0.90

11.38

Air toxics NEPM

t/yr

g/vehicle

t/yr

g/heater

woodheater/car

  Benzene

382

211

274

2582

12.2

  Toluene

712

393

76

716

1.8

  Formaldehyde

117

65

454

4279

66.2

  Xylene

589

325

42

396

1.2

  PAH

39

22

100

943

43.8


For both tables, emissions per vehicle and per wood heater were calculated by dividing total emissions (NSW DECC Emissions Inventory, Tables ES4 in the domestic-commercial and on-road emissions in the 2008 inventory, ES4 and and ES1.4 in the 2003 inventory) by the number of woodheaters (106,100) and passenger cars (1.811 million in 2007) in Sydney. 

 

2003 Emissions - Sydney

Cars

Woodheaters

Ratio

Ambient AQ NEPM

t/yr

kg/vehicle

t/yr

kg/heater

woodheater/car

  PM2.5

797

0.44

4503

42.44

96.39

  VOC (ozone precursor)

26066

14.39

9524

89.76

6.24

  CO

323953

178.88

27889

262.86

1.47

  NOX

38175

21.08

361

3.40

0.16

  SO2

645

0.36

73

0.68

1.92

Air toxics NEPM

t/yr

g/vehicle

t/yr

g/heater

woodheater/car

  Benzene

1217

672

463

4364

6.49

  Toluene

1311

724

148

1395

1.93

  Formaldehyde

340

188

777

7323

38.95

  Xylene

1815

1002

71.9

678

0.68

  PAH

120

66

69.2

652

9.82

 
ABC News April 2008: Wood smoke worse that car exhausts
"In the limited amount of studies that have been done so far that have directly compared smoke from fires with the same level of particulates and smoke from car exhaust, industry have all tended to show that the effects from the wood smoke are actually worse for lung conditions than a similar amount from, say, car exhausts"

Norwegian Study comparing genetic damage from woodsmoke and traffic in human cell lines: "In conclusion, woodsmoke particulate matter (WSPM) generated more DNA damage than traffic-generated PM per unit mass in human cell lines, possibly due to the high level of polycyclic aromatic hydrocarbons in WSPM. This suggests that exposure to WSPM might be more hazardous than PM collected from vehicle exhaust with respect to development of lung cancer."

Greenhouse gases.
 



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