Table 3a. Molecular Weights Associated With the Monoterpenes Detected by PTR-MS			
Compound	m/z (mass + 1)	Structure	Description
limonene	69, 81a, 82, 95, 96, 137, 138b 	C10H16H+, C6H9H+	monoterpene, fragments and isotopes
	107c, 108, 123d*,124, 133, 151*, 152, 169*, 170	C10H16O2H+	uncalibrated oxidation product: limononaldehyde, fragments, and isotopes
	139, 140	C9H14OH+	uncalibrated oxidation product: limonaketone and isotope
	57, 69, 70, 71, 73, 75, 77, 83, 85, 87, 89, 93, 97, 99, 101, 103, 109, 111*, 113*, 115, 121, 125, 127, 129, 131, 135, 141*, 143, 149, 153, 155*, 156, 157, 165, 167, 171, 181, 183, 185, 187, 200d, 218d		unidentified oxidation products
myrcene	81, 82, 137, 138	C10H16H+, C6H9H+	monoterpene, fragments and isotopes
	57, 64e, 65, 71, 73, 75, 77, 83, 85, 87, 89, 93, 97, 99, 101, 103, 111*, 113*, 115, 125, 127, 129, 139*, 141, 143, 145, 153, 155*, 159* 		unidentified oxidation products
3-carene	81, 82, 137, 138 	C10H16H+, C6H9H+	monoterpene, fragments and isotopes
	107, 108, 123*,124, 133, 151*, 152, 169*, 170	C10H16O2H+	uncalibrated oxidation product: caronaldehyde, fragments, and isotopes
	71, 73, 75, 77, 79, 83, 85, 87, 89, 93, 94, 97, 99, 101, 103, 107, 109, 111, 113, 115, 121, 123*, 124, 125, 127, 129, 133, 135, 139*, 141*, 142, 151*, 153, 155*, 157, 167, 169*, 181, 183		unidentified oxidation products
alpha-pinene	81, 82, 137, 138	C10H16H+, C6H9H+	monoterpene, fragments and isotopes
	 71, 72, 99, 107, 108, 109, 123*, 151, 152, 169, 170 f 	C10H16O2H+	uncalibrated oxidation product: pinonaldehyde, fragments, and isotopes 
	69, 73, 75, 83, 85, 87, 89, 94d, 97, 101, 103, 111*, 113*, 115, 121, 125, 127, 129, 131, 139, 141*, 153, 155*, 157, 165, 167, 171, 183, 185, 200e 		unidentified oxidation products
aIons associated with parent terpenes listed in bold font represent ions > 20% of the unfragmented parent terpene. 
bAll monoterpenes occur predominantly on the parent m/z 137 and the fragment m/z 81 ions, with a small fraction (< 20%) occurring on the 13C isotope with m/z (138, 82). 
cUnidentified oxidation products in bold font are ions with > 5% yield (on a mole basis) from the parent terpene.  
dUnidentified oxidation products with asterisks represent ions that were observed in the canopy air of a coniferous forest in California by PTR-MS [Holzinger et al., 2005]. 
eEven mass-to-charge ratio oxidation products that are not carbon isotopes of other oxidation products are likely gas-phase nitrogen containing products, e.g., organic nitrates. 
fFragments were determined from correlations with m/z 151 (the dominant pinonaldehyde ion) that also agreed well with fragment ions reported elsewhere for pinonaldehyde [Wisthaler et al., 2001]. Additional fragment ions reported by Wisthaler et al. [2001], m/z 43 and 81, were excluded from the pinonaldehyde concentration due to interference by other compounds.