High Levels of Isoprene in the Marine Boundary Layer of the Arabian Sea during Spring Inter-Monsoon: Role of Phytoplankton Blooms

Abstract. The diurnal evolution of a cloud free, marine boundary layer is studied by means of experimental measurements and numerical simulations. Experimental data belong to an investigation of the mixing height over inner Danish waters. The mixed-layer height measured over the sea is generally nearly constant, and does not exhibit the diurnal cycle characteristic of boundary layers over land. A case study, during summer, showing an anomalous development of the mixed layer under unstable and nearly neutral atmospheric conditions, is selected in the campaign. Subsidence is identified as the main physical mechanism causing the sudden decrease in the mixing layer height. This is quantified by comparing radiosounding profiles with data from numerical simulations of a mesoscale model, and a large-eddy simulation model. Subsidence not only affects the mixing layer height, but also the turbulent fluctuations within it. By analyzing wind and scalar spectra, the role of subsidence is further investigated and a more complete interpretation of the experimental results emerges.

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Modeling the chemistry of the marine boundary layer: Sulphate formation and the role of sea-salt aerosol particles

Journal of Geophysical Research Atmospheres ◽

10.1029/1999jd901073 ◽

2000 ◽

Vol 105 (D9) ◽

pp. 11671-11698 ◽

Cited By ~ 27

Author(s):

Ad van den Berg ◽

Frank Dentener ◽

Jos Lelieveld

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Aerosol Particles ◽

Sea Salt ◽

Sea Salt Aerosol

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Distribution of ozone in the marine boundary layer of Arabian Sea prior to monsoon: Prevailing airmass and effect of aerosols

Atmospheric Environment ◽

10.1016/j.atmosenv.2013.02.049 ◽

2013 ◽

Vol 74 ◽

pp. 18-28 ◽

Cited By ~ 2

Author(s):

Prabha R. Nair ◽

Liji Mary David ◽

S. Aryasree ◽

K. Susan George

Keyword(s):

Boundary Layer ◽

Arabian Sea ◽

Marine Boundary Layer

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Enhanced production of oxidised mercury over the tropical Pacific Ocean: a key missing oxidation pathway

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-21541-2013 ◽

2013 ◽

Vol 13 (8) ◽

pp. 21541-21572

Author(s):

F. Wang ◽

A. Saiz-Lopez ◽

A. S. Mahajan ◽

J. C. Gómez Martín ◽

D. Armstrong ◽

...

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Thermal Dissociation ◽

Oxidation Mechanism ◽

Elemental Mercury ◽

Atmospheric Mercury ◽

Mercury Oxidation ◽

Enhanced Production ◽

Daily Variability

Abstract. Mercury is a contaminant of global concern. It is transported in the atmosphere primarily as gaseous elemental mercury, but its reactivity and deposition to the surface environment, through which it enters the aquatic food chain, is greatly enhanced following oxidation. Measurements of oxidised mercury in the polar to sub-tropical marine boundary layer have suggested that photolytically produced bromine atoms are the primary oxidant of mercury. We report year-round measurements of elemental and oxidised mercury, along with ozone, halogen oxides (IO and BrO) and nitrogen oxides (NO2), in the marine boundary layer over the Galápagos Islands in the Equatorial Pacific. Elemental mercury concentration remained low throughout the year, while considerable concentrations of oxidised mercury occurred around midday. Our results show that the production of oxidised mercury in the tropical marine boundary layer cannot be accounted for by only bromine oxidation, or by the inclusion of ozone and hydroxyl. A two-step oxidation mechanism where the HgBr intermediate is further oxidised to Hg(II) depends critically on the stability of HgBr. If the current paradigm is considered, another oxidant is needed to explain more than 50% of the observed oxidised mercury. We show that atomic iodine could play the role of the missing oxidant, explaining not only the Hg(II) levels observed, but also the daily variability. However, more recent theoretical calculations indicate that the thermal dissociation rate of HgBr is much faster, by an order of magnitude, than previously reported, which implies that only trace gases at relatively high mixing ratios forming stable complexes with HgBr (such as HO2 and NO2) could compete to generate levels of Hg(II) similar to those observed in our study. Nevertheless, the daily variability of oxidised mercury is not well accounted for by using these new theoretically estimated rates. Furthermore, correlation analysis does not support a major role of NO2 or HO2. We conclude that the key pathway that significantly enhances atmospheric mercury oxidation and deposition to the tropical oceans is missing from the current understanding of atmospheric mercury oxidation.

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Net ozone production and its relationship to NO<sub>x</sub> and VOCs in the marine boundary layer around the Arabian Peninsula

10.5194/acp-2019-1031 ◽

2019 ◽

Author(s):

Ivan Tadic ◽

John N. Crowley ◽

Dirk Dienhart ◽

Philipp Eger ◽

Hartwig Harder ◽

...

Keyword(s):

Boundary Layer ◽

Red Sea ◽

General Circulation ◽

Arabian Sea ◽

Marine Boundary Layer ◽

Arabian Peninsula ◽

Water Vapor Pressure ◽

Ozone Production ◽

The Mediterranean ◽

Northern Red Sea

Abstract. Strongly enhanced tropospheric ozone mixing ratios have been reported in the Arabian Basin, a region with intense solar radiation and high concentrations of ozone precursors such as nitrogen oxides and volatile organic compounds. To analyze photochemical ozone production in the marine boundary layer (MBL) around the Arabian Peninsula, we use ship-borne observations of NO, NO2, O3, OH, HO2, HCHO, actinic flux, water vapor, pressure and temperature obtained during the summer 2017 Air Quality and Climate in the Arabian Basin (AQABA) campaign, compare them to simulation results of the ECHAM-MESSy atmospheric chemistry (EMAC) general circulation model. Net ozone production rates (NOPR) were greatest over the Gulf of Oman, the Northern Red Sea and the Arabian Gulf with median values of 14 ppbv day−1, 16 ppbv day−1 and 28 ppbv day−1, respectively. NOPR over the Mediterranean, the Southern Red Sea and the Arabian Sea did not significantly deviate from zero; however, results for the Arabian Sea indicate weak net ozone production of 5 ppbv day−1, and net ozone destruction over the Mediterranean and the Southern Red Sea with −2 ppbv day−1 and −4 ppbv day−1, respectively. Constrained by measured HCHO/NO2-ratios, our photochemistry calculations show that net ozone production in the MBL around the Arabian Peninsula occurs mostly in a transition regime between NOx and VOC-limitation with a tendency towards NOx-limitation except over the Northern Red Sea and the Oman Gulf.

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Net ozone production and its relationship to nitrogen oxides and volatile organic compounds in the marine boundary layer around the Arabian Peninsula

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-6769-2020 ◽

2020 ◽

Vol 20 (11) ◽

pp. 6769-6787 ◽

Cited By ~ 2

Author(s):

Ivan Tadic ◽

John N. Crowley ◽

Dirk Dienhart ◽

Philipp Eger ◽

Hartwig Harder ◽

...

Keyword(s):

Boundary Layer ◽

Volatile Organic Compounds ◽

Organic Compounds ◽

Red Sea ◽

Arabian Sea ◽

Marine Boundary Layer ◽

Arabian Peninsula ◽

Volatile Organic ◽

The Mediterranean ◽

Northern Red Sea

Abstract. Strongly enhanced tropospheric ozone (O3) mixing ratios have been reported in the Arabian Basin, a region with intense solar radiation and high concentrations of O3 precursors such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). To analyze photochemical O3 production in the marine boundary layer (MBL) around the Arabian Peninsula, we use shipborne observations of NO, NO2, O3, OH, HO2, HCHO, the actinic flux, water vapor, pressure and temperature obtained during the summer 2017 Air Quality and Climate in the Arabian Basin (AQABA) campaign, and we compare them to simulation results from the ECHAM-MESSy Atmospheric Chemistry (EMAC) general circulation model. Net O3 production rates (NOPRs) were greatest over both the Gulf of Oman and the northern Red Sea (16 ppbv d−1) and over the Arabian Gulf (32 ppbv d−1). The NOPR over the Mediterranean, the southern Red Sea and the Arabian Sea did not significantly deviate from zero; however, the results for the Arabian Sea indicated weak net O3 production of 5 ppbv d−1 as well as net O3 destruction over the Mediterranean and the southern Red Sea with values of −1 and −4 ppbv d−1, respectively. Constrained by HCHO∕NO2 ratios, our photochemistry calculations show that net O3 production in the MBL around the Arabian Peninsula mostly occurs in NOx-limited regimes with a significant share of O3 production occurring in the transition regime between NOx limitation and VOC limitation over the Mediterranean and more significantly over the northern Red Sea and Oman Gulf.

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