Stable bromine isotopic composition of atmospheric CH₃Br

Figures & data

Table 1 Results from concentration and isotope measurements

Sample ID	Field campaign	Sample date	δ^81Br [SMOB] (‰)	RSD^2 (‰)	N	Mixing ratio ppt	SD ppt	Sample type	Sample volume (m^3)	BT region	BL height (m)
1	Abisko	2 August 2011	−0.01	0.12	2	10.4	2.3	Free air	4.5	1	583
2	Abisko	2 August 2011	−0.14	0.43	1	9.3	2.1	Free air	2.7	1	118
3	Abisko	3 August 2011	−0.04	0.43	1	14.1	3.2	Free air	3.4	1	497
4	Abisko	3 August 2011	0.48	0.43	1	5.4	1.2	Free air	3.6	1	185
5	Abisko	3 August 2011	−0.25	0.43	1	5.0	1.1	Dry soil	3.0	–	–
6	Abisko	4 August 2011	0.88	0.43	1	6.6	1.5	Dry soil	3.0	–	–
7	Abisko	4 August 2011	0.15	0.43	1	1.7	0.4	Dry soil	4.6	–	–
8^1	Abisko	5 August 2011	0.04	0.43	1	10.4	2.3	Damp soil	3.8	–	–
9	Abisko	5 August 2011	1.42	0.43	1	8.2	1.8	Damp soil	3.6	–	–
10	Stockholm	29 September 2011	−0.08	0.43	3	15.8	1.6	Free air	4.8	4	450
11	Stockholm	3 October 2011	1.17	0.43	1	12.6	1.4	Free air	4.8	2	527
12	Stockholm	4 October 2011	0.81	0.43	1	14.5	1.5	Free air	4.8	2	1476
13	Stockholm	5 October 2011	1.75	0.13	2	12.6	1.3	Free air	4.8	2	1016
14	Stockholm	18 October 2011	0.47	0.27	2	12.9	1.6	Free air	5.0	5	960
15	Stockholm	19 October 2011	−0.47	0.43	1	18.3	1.8	Free air	4.8	3	872

¹This sample was compromised by free air because of leakage around the sampler intake and is not included in statistical calculations.

²The standard deviations for isotope values based on one measurement were set to 0.43‰ (in italic), which was the largest value, found throughout this campaign for triple injections.

Fig. 1 Back trajectories (BTs) of sampled air, as determined by HYSPLIT4 model. The arrows are describing the path of the air mass BTs and the dotted ellipses are indicating the area where it was last in contact with the ground (i.e. in the boundary layer). The BT 3 contact region is described by the entire arrow (dotted margins).

Fig. 2 Methyl bromide isotope composition as a function of concentration for Stockholm free air (filled circles), Abisko free air (open squares), Abisko dry soil air (filled triangles) and Abisko damp-soil air (cross). A logarithmic regression line (dashed, grey) shows the enrichment in δ⁸¹Br as the CH₃Br concentration decreased in the Stockholm free air. The grey-shaded area indicates the lowest values found throughout both field campaigns and indicates a range of suggested background composition.