Direct detection of atmospheric atomic bromine leading to mercury and ozone depletion.

Bromine atoms play a central role in atmospheric reactive halogen chemistry, depleting ozone and elemental mercury, thereby enhancing deposition of toxic mercury, particularly in the Arctic near-surface troposphere. However, direct bromine atom measurements have been missing to date, due to the lack of analytical capability with sufficient sensitivity for ambient measurements. Here we present direct atmospheric bromine atom measurements, conducted in the springtime Arctic. Measured bromine atom levels reached 14 parts per trillion (ppt, pmol mol-1; 4.2 × 108 atoms per cm-3) and were up to 3-10 times higher than estimates using previous indirect measurements not considering the critical role of molecular bromine. Observed ozone and elemental mercury depletion rates are quantitatively explained by the measured bromine atoms, providing field validation of highly uncertain mercury chemistry. Following complete ozone depletion, elevated bromine concentrations are sustained by photochemical snowpack emissions of molecular bromine and nitrogen oxides, resulting in continued atmospheric mercury depletion. This study provides a breakthrough in quantitatively constraining bromine chemistry in the polar atmosphere, where this chemistry connects the rapidly changing surface to pollutant fate.

Springtime Nitrogen Oxide-Influenced Chlorine Chemistry in the Coastal Arctic.

Atomic chlorine (Cl) is a strong atmospheric oxidant that shortens the lifetimes of pollutants and methane in the springtime Arctic, where the molecular halogens Cl2 and BrCl are known Cl precursors. Here, we quantify the contributions of reactive chlorine trace gases and present the first observations, to our knowledge, of ClNO2 (another Cl precursor), N2O5, and HO2NO2 in the Arctic. During March - May 2016 near Utqiagvik, Alaska, up to 21 ppt of ClNO2, 154 ppt of Cl2, 27 ppt of ClO, 71 ppt of N2O5, 21 ppt of BrCl, and 153 ppt of HO2NO2 were measured using chemical ionization mass spectrometry. The main Cl precursor was calculated to be Cl2 (up to 73%) in March, while BrCl was a greater contributor (63%) in May, when total Cl production was lower. Elevated levels of ClNO2, N2O5, Cl2, and HO2NO2 coincided with pollution influence from the nearby town of Utqiagvik and the North Slope of Alaska (Prudhoe Bay) Oilfields. We propose a coupled mechanism linking NOx with Arctic chlorine chemistry. Enhanced Cl2 was likely the result of the multiphase reaction of Cl-(aq) with ClONO2, formed from the reaction of ClO and NO2. In addition to this NOx-enhanced chlorine chemistry, Cl2 and BrCl were observed under clean Arctic conditions from snowpack photochemical production. These connections between NOx and chlorine chemistry, and the role of snowpack recycling, are important given increasing shipping and fossil fuel extraction predicted to accompany Arctic sea ice loss.

Observation of Road Salt Aerosol Driving Inland Wintertime Atmospheric Chlorine Chemistry.

Inland sources of particulate chloride for atmospheric nitryl chloride (ClNO2) formation remain unknown and unquantified, hindering air quality assessments. Globally each winter, tens of millions of tons of road salt are spread on roadways for deicing. Here, we identify road salt aerosol as the primary chloride aerosol source, accounting for 80-100% of ClNO2 formation, at an inland urban area in the wintertime. This study provides experimental evidence of the connection between road salt and air quality through the production of this important reservoir for nitrogen oxides and chlorine radicals, which significantly impact atmospheric composition and pollutant fates. A numerical model was employed to quantify the contributions of chloride sources to ClNO2 production. The traditional method for simulating ClNO2 considers chloride to be homogeneously distributed across the atmospheric particle population; yet, we show that only a fraction of the particulate surface area contains chloride. Our new single-particle parametrization considers this heterogeneity, dramatically lowering overestimations of ClNO2 levels that have been routinely reported using the prevailing methods. The identification of road salt as a ClNO2 source links this common deicing practice to atmospheric composition and air quality in the urban wintertime environment.

p107 regulates neural precursor cells in the mammalian brain.

Here we show a novel function for Retinoblastoma family member, p107 in controlling stem cell expansion in the mammalian brain. Adult p107-null mice had elevated numbers of proliferating progenitor cells in their lateral ventricles. In vitro neurosphere assays revealed striking increases in the number of neurosphere forming cells from p107(-/-) brains that exhibited enhanced capacity for self-renewal. An expanded stem cell population in p107-deficient mice was shown in vivo by (a) increased numbers of slowly cycling cells in the lateral ventricles; and (b) accelerated rates of neural precursor repopulation after progenitor ablation. Notch1 was up-regulated in p107(-/-) neurospheres in vitro and brains in vivo. Chromatin immunoprecipitation and p107 overexpression suggest that p107 may modulate the Notch1 pathway. These results demonstrate a novel function for p107 that is distinct from Rb, which is to negatively regulate the number of neural stem cells in the developing and adult brain.