Measurements and modelling of I2, IO, OIO, BrO and NO3 in the mid-latitude marine boundary layer

[摘要] Time series observations of molecular iodine (I₂), iodineoxides (IO, OIO), bromine oxide (BrO), and the nitrate radical(NO₃) in the mid-latitude coastal marine boundary layer(MBL) are reported. Measurements were made using a new long-pathDOAS instrument during a summertime campaign at Mace Head on theB³Π(0⁺_u)-X¹Σ⁺_g electronic transitionbetween 535 and 575 nm.The I₂ mixing ratio was found tovary from below the detection limit (~5 ppt) up to a nighttimemaximum of 93 ppt. Along with I₂, observations of IO, OIOand NO₃ were also made during the night.Surprisingly, IOand OIO were detected at mixing ratios up to 2.5 and 10.8 ppt,respectively.A model is employed to show that the reactionbetween I₂ and NO₃ is the likely nighttime source ofthese radicals.The BrO mixing ratio varied from below thedetection limit at night (~1 ppt) to a maximum of 6 ppt in thefirst hours after sunrise.A bromine chemistry model is used tosimulate the diurnal behaviour of the BrO radical, demonstrating theimportance of halogen recycling through sea-salt aerosol. In thesame campaign a zenith sky DOAS was employed to determine the columndensity variation of NO₃ as a function of solar zenith angle(SZA) during sunrise, from which vertical profiles of NO₃through the troposphere were obtained.On several occasions apositive gradient of NO₃ was observed over the first 2 km,possibly due to dimethyl sulphide (DMS) removing NO₃ at theocean surface.

[学科分类] 大气科学