Gaseous (DMS, MSA, SO2, H2SO4 and DMSO) and particulate (sulfate and methanesulfonate) sulfur species over the northeastern coast of Crete

[摘要] A detailed study of the levels, the temporal and diurnal variability of the maincompounds involved in the biogenic sulfur cycle was carried out in Crete (EasternMediterranean) during the Mediterranean Intensive Oxidant Study (MINOS) fieldexperiment in July-August 2001. Intensive measurements of gaseous dimethylsulfide(DMS), dimethylsulfoxide (DMSO), sulfur dioxide (SO₂), sulfuric(H₂SO₄) and methanesulfonic acids (MSA) and particulate sulfate(SO₄^2-) and methanesulfonate (MS^-) have been performed during the campaign.

Dimethylsulfide (DMS) levels ranged from 2.9 to 136 pmol·mol^-1 (mean value of21.7 pmol·mol^-1) and showed a clear diurnal variation with daytime maximum. Duringnighttime DMS levels fall close or below the detection limit of 2pmol·mol^-1. Concurrent measurements of OH and NO₃ radicals during the campaign indicate thatNO₃ levels can explain most of the observed diurnal variation of DMS. Dimethylsulfoxide(DMSO) ranged between 0.02 and 10.1 pmol·mol^-1 (mean value of1.7 pmol·mol^-1) and presents a diurnal variation similar to that ofDMS. SO₂ levels ranged from 220 to 2970 pmol·mol^-1 (mean value of1030 pmol·mol^-1), while nss-SO₄^2- and MS^- ranged from 330 to7100 pmol·mol^-1, (mean value of 1440 pmol·mol^-1) and 1.1 to37.5 pmol·mol^-1 (mean value of 11.5 pmol·mol^-1) respectively.

Of particular interest are the measurements of gaseous MSA and H₂SO₄. MSA rangedfrom below the detection limit (3x10⁴) to 3.7x10⁷molecules cm^-3, whereas H₂SO₄ ranged between1x10⁵ and 9.0x10⁷ molecules cm^-3. The measuredH₂SO₄ maxima are among the highest reported in literature and can be attributed to highinsolation, absence of precipitation and increased SO₂ levels in the area. From the concurrentSO₂, OH, and H₂SO₄ measurements a sticking coefficient of0.52±0.28 was calculated for H₂SO₄. From the concurrent MSA, OH, and DMS measurements the yield of gaseous MSA fromthe OH-initiated oxidation of DMS was calculated to range between0.1-0.4%. This low MSA yield implies that gaseous MSA levels can not account for the observedMS^- levels. Heterogeneous reactions of DMSO on aerosols should be considered to explain theobserved levels of MS^-.

[学科分类] 大气科学