Table 3.5.

Some trace biogenic gases in the atmosphere.

Compound	Formula	Concentration (ppb)		Mean residence time	Percentage of sink due to OH
		Expecteda	Actualb
Carbon compounds
Methane	CH4	10− 148	1830	9 years	90
Carbon monoxide	CO	10− 51	45–250	60 days	80
Isoprene	CH2 C(CH3)—CH CH2		0.2–10.0	< 1 day	100
Nitrogen compounds
Nitrous oxide	N2O	10− 22	320	120 years	0
Nitric oxides	NOx	10− 13	0.02–10.0	1 day	100
Ammonia	NH3	10− 63	0.08–5.0	5 days	< 2
Sulfur compounds
Dimethylsulfide	(CH3)2S		0.004–0.06	1 day	50
Hydrogen sulfide	H2S		< 0.04	4 days	100
Carbonyl sulfide	COS	0	0.50	5 years	20
Sulfur dioxide	SO2	0	0.02–0.10	3 days	50

^aApproximate values in equilibrium with an atmosphere containing 21% O₂ (Chameides and Davis, 1982).

^bFor short-lived gases, the value is the range expected in remote, unpolluted atmospheres.