Table 1.

Field sampling results for δ¹⁵N-NO₂ and estimated δ¹⁵N-NO_x based on isotopic fractionation calculations, as well as the results for δ¹⁵N-NO₃ for Calipatria and Thermal. All reported units are per mil, ‰.

	Calipatria			Thermal
	δ15N-NO2	δ15N-NOx	δ15N-tNO3	δ15N-NO2	δ15N-NOx	δ15N-tNO3
Jun 2022	− 13.2	− 13.6	− 0.02	No measurements
Jul 2022	− 13.4	− 14.1	− 2.6	− 14.3	− 16.1	− 4.5
Aug 2022	− 14.4	− 14.9	− 9.8	− 4.6	− 8.0	− 4.8
Sep 2022	− 15.6	− 16.6	− 3.4	− 5.9	− 8.0	N/A
Oct 2022	− 5.3	− 6.1	− 1.1	− 9.7	− 12.0	− 8.2
Nov 2022	− 12.4	− 13.4	− 2.9	1.8	0.2	2.8
Dec 2022	− 13.3	− 14.9	− 2.9	− 7.5	− 9.1	3.4
Jan 2023	− 9.6	− 11.6	− 0.7	− 1.5	− 3.2	3.9
Feb 2023	− 14.8	− 15.5	0.1	− 11.3	− 12.0	2.6
Apr 2023	− 16.0	− 16.0	− 3.4	− 6.8	− 7.6	1.8
Average	− 12.8	− 13.7	− 2.7	− 6.6	− 8.4	− 0.38