Table 8.1: Clean air background concentrations of some atmospheric gases in New Zealand
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| Gas |
Mean value |
Unit |
Accuracy +/- |
Seasonal range |
Comment |
|---|---|---|---|---|---|
Carbon dioxide (CO2) |
368 |
ppm |
1.0 |
1.0 |
Increasing at 0.4% per year |
Carbon monoxide (CO) |
0.055 |
ppm |
0.005 |
0.015 |
Strong season and space variation |
Nitrous oxide (N2O) |
0.316 |
ppm |
0.001 |
0.001 |
Little space and time variation, increasing at 0.6% per year |
Methane (CH4) |
1.75 |
ppm |
0.01 |
0.03 |
Local sources can bias (eg, strong agricultural sources) |
Hydrogen (H2) |
0.70 |
ppm |
0.01 |
0.01 |
Reasonably constant |
Sulphur dioxide (SO2) |
0.016 |
ppb |
0.012 |
0.016 |
Maximum in summer, practically zero in winter |
Nitrogen dioxide (NO2) |
< 0.5 |
ppb |
0.5 |
na |
Estimated from urban monitoring |
Ozone (O3) |
30 |
ppb |
2.0 |
15 |
Highest New Zealand levels are often in clean air, and are strongly seasonal. This level is 'natural'. |
Particulates (as PM10) |
1.0 |
µg/m3 |
0.1 |
1.0 |
All sea salt |
Chlorofluorocarbon (CFC12) |
0.50 |
ppm |
0.05 |
0.01 |
Recent global increase |
Benzene (C6H6) |
0.05 |
ppb |
0.01 |
na |
Can be zero in ultra clean air, over 30 ppb in city contaminated air |
Other toxics |
< dl |
est. |
na |
Not measured, but most are below detection limits for the most sensitive equipment |
|
Nitrogen (N2) |
780,900 |
ppm |
est. |
– |
Not measured routinely in New Zealand |
Oxygen (O2) |
209,400 |
ppm |
est. |
– |
Not measured routinely in New Zealand |
Argon (Ar) |
9,300 |
ppm |
est. |
– |
Not measured routinely in New Zealand |
Other inert gases |
20 |
ppm |
est. |
– |
Not measured routinely in New Zealand |
