The geochemical cycling of reactive chlorine through the marine troposphere

Heterogeneous reactions involving sea‐salt aerosol in the marine troposphere are the major global source for volatile inorganic chlorine. We measured reactant and product species hypothesized to be associated with these chemical transformations as a function of phase, particle size, and altitude over the North Atlantic Ocean during the summer of 1988. Concentrations of HCl were typically less than 1.0 ppbv near the sea surface and decreased with altitude and with distance from the U.S. east coast. Concentrations of Cl volatilized from aerosols were generally equivalent to the corresponding concentrations of HCl and ranged from less than detection limits to 125 nmol m−3 STP. Highest absolute and percentage losses of particulate Cl were typically associated with elevated concentrations of anthropogenic combustion products. Concentrations of product nss SO42− and N03− in coarse aerosol fractions indicate that on average only 38% of measured Cl− deficits could be accounted for by the combined effects of acid‐base desorption and reactions involving nonacidic N gases. We hypothesize a mechanism for the Cl loss initiated by reaction of O3 at sea‐salt aerosol surfaces, generating Cl2 followed by rapid photochemical conversion of Cl2 to HCl via Cl atoms (Cl˙) and eventual recapture of HCl by the aerosol. Simulations with a zero‐dimension (0‐D) photochemical model suggest that oxidation by Cl˙ may be an important tropospheric sink for dimethyl sulfide and hydrocarbons. Under low‐NOx conditions, the rapid cycling of reactive Cl would provide a catalytic loss mechanism for O3, which would possibly explain the low O3 concentrations often observed above the world\u27s oceans

Modelling human choices: MADeM and decision‑making

Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)

Sulfur in the western North Atlantic Ocean atmosphere: Results from a summer 1988 ship/aircraft experiment

To investigate the relative importance of anthropogenic versus marine sources of sulfur in the North Atlantic Ocean troposphere, sulfur species were measured from aircraft, ship, and island based platforms as part of the Global Change Expedition/Coordinated Air‐Sea Experiment/Western Atlantic Ocean Experiment conducted during the summer of 1988. Four synoptic meteorological cases were examined: flow from highly populated North America, lightly populated North America, tropical oceanic regions, and polar oceanic regions. Literature values suggest that 2–10 μmol m−2 day−1 of (CH3)2S are emitted from the ocean to the atmosphere in marine regions associated with the first three synoptic cases. Data from this experiment indicate that 36, 16, and 14 μmol m−2 day−1, for the highly populated North America, lightly populated North America, and tropical oceanic regions synoptic cases, respectively, were deposited to the ocean\u27s surface. Differences between previously estimated natural emissions and calculated deposition suggest that anthropogenic sources of sulfur contribute significantly to sulfur deposition for these cases. The sulfur deposition rate for the polar oceanic regions synoptic case was 20 μmol m−2 day−1 . Given the larger range of literature values for the corresponding (CH3)2S emission rate (1–14 μmol m−2 day−1 ) , however, the relative importance of the nonmarine S source is less certain in this case. Copyright 1990 by the American Geophysical Union

The geochemical cycling of reactive chlorine through the marine troposphere

Heterogeneous reactions involving sea‐salt aerosol in the marine troposphere are the major global source for volatile inorganic chlorine. We measured reactant and product species hypothesized to be associated with these chemical transformations as a function of phase, particle size, and altitude over the North Atlantic Ocean during the summer of 1988. Concentrations of HCl were typically less than 1.0 ppbv near the sea surface and decreased with altitude and with distance from the U.S. east coast. Concentrations of Cl volatilized from aerosols were generally equivalent to the corresponding concentrations of HCl and ranged from less than detection limits to 125 nmol m STP. Highest absolute and percentage losses of particulate Cl were typically associated with elevated concentrations of anthropogenic combustion products. Concentrations of product nss SO and N0 in coarse aerosol fractions indicate that on average only 38% of measured Cl deficits could be accounted for by the combined effects of acid‐base desorption and reactions involving nonacidic N gases. We hypothesize a mechanism for the Cl loss initiated by reaction of O at sea‐salt aerosol surfaces, generating Cl followed by rapid photochemical conversion of Cl to HCl via Cl atoms (Cl˙) and eventual recapture of HCl by the aerosol. Simulations with a zero‐dimension (0‐D) photochemical model suggest that oxidation by Cl˙ may be an important tropospheric sink for dimethyl sulfide and hydrocarbons. Under low‐NO conditions, the rapid cycling of reactive Cl would provide a catalytic loss mechanism for O, which would possibly explain the low O concentrations often observed above the world's oceans.Engineering and Applied Science