23 research outputs found
History and characterization of atmospheric black carbon in the Anthropocene
Black carbon aerosols (BC) from incomplete combustion have substantial effects on the atmosphere and climate, but climate forecasting is poorly constrained due to uncertainties in atmospheric lifetime and removal rates. Herein, we detail the recent history, characteristics, and composition of BC deposited in rain from Australia and ice cores from Antarctica. Results show new complex particle characteristics and an increase in BC in West Antarctica driven by changing emissions and atmospheric transport conditions
Inelastic collisions of CaH with He at cryogenic temperatures
Using helium buffer gas cooling, we have prepared dense samples of ground-state molecular calcium monohydride (CaH X 2Σ) at cryogenic temperatures. We have used optical pumping to polarise the spin state of the CaH molecules and we have measured the inelastic collisions of molecular CaH with atomic helium at temperatures from 2 to 7 K. The measured CaH electronic spin depolarisation rate coefficient increases rapidly with increasing temperature, increasing from 2 × 10−13 cm3 s−1 to over 10−11 cm3 s−1. The strong dependence of rate coefficient on temperature is attributed to the CaH population in the first excited rotational state
Experimental biogeography: the role of environmental gradients in high geographic diversity in Cape Proteaceae
One of the fundamental dimensions of biodiversity is the rate of species turnover across geographic distance. The Cape Floristic Region of South Africa has exceptionally high geographic species turnover, much of which is associated with groups of closely related species with mostly or completely non-overlapping distributions. A basic unresolved question about biodiversity in this global hotspot is the relative importance of ecological gradients in generating and maintaining high geographic turnover in the region. We used reciprocal transplant experiments to test the extent to which abiotic environmental factors may limit the distributions of a group of closely related species in the genus Protea (Proteaceae), and thus elevate species turnover in this diverse, iconic family. We tested whether these species have a “home site advantage” in demographic rates (germination, growth, mortality), and also parameterized stage-structured demographic models for the species. Two of the three native species were predicted to have a demographic advantage at their home sites. The models also predicted, however, that species could maintain positive population growth rates at sites beyond their current distribution limits. Thus the experiment suggests that abiotic limitation under current environmental conditions does not fully explain the observed distribution limits or resulting biogeographic pattern. One potentially important mechanism is dispersal limitation, which is consistent with estimates based on genetic data and mechanistic dispersal models, though other mechanisms including competition may also play a role
Air Quality in Puerto Rico in the Aftermath of Hurricane Maria: A Case Study on the Use of Lower-Cost Air Quality Monitors
In
the aftermath of Hurricane Maria, the electricity grid in Puerto Rico was
devastated, with over 90% of the island without electricity; as of December
2017, about 50% of the island lacked electricity, and power outages were common
elsewhere. Backup generators are widely used, sometimes as the main source of
electricity. The hurricane also damaged the island’s existing air monitoring
network and the University of Puerto Rico’s observing facilities. We deployed
four lower-cost air quality monitors (Real-time Affordable Multi-Pollutant or
RAMP monitors) and a black carbon (BC) monitor in the San Juan Metro Area in
November 2017. The first month of data collected with the RAMPs showed high
sulfur dioxide (SO2) and carbon monoxide (CO) concentrations of
varying magnitudes each night. SO2 and CO are strongly correlated (r2
>0.9) at two sites ~5 km apart (University of Puerto Rico and an
industrial area, Puerto Nuevo), suggesting a single source type. BC measured at
the UPR site is also well correlated with CO and SO2. While the
RAMPs are not certified as a federal equivalent method, the RAMP SO2
data suggest that the EPA’s daily 1-hour threshold for SO2
(75 ppb) was exceeded on almost 80% of the first 30 days of deployment
(November-December 2017). The widespread reliance on generators for regular
electric supply in the aftermath of Hurricane Maria appears to have increased
air pollution in San Juan
Chemical reactions of atomic lithium and molecular calcium monohydride at 1 K
Using cryogenic helium buffer-gas cooling, we have prepared dense samples of atomic lithium and molecular calcium monohydride at temperatures as low as 1 K. We have measured the Li+CaH→LiH+Ca chemical reaction, observed in both the accelerated disappearance of CaH in the presence of high densities of lithium and in the appearance of the LiH molecule
Air Quality in Puerto Rico in the Aftermath of Hurricane Maria: A Case Study on the Use of Lower-Cost Air Quality Monitors
In
the aftermath of Hurricane Maria, the electricity grid in Puerto Rico was
devastated, with over 90% of the island without electricity; as of December
2017, about 50% of the island lacked electricity, and power outages were common
elsewhere. Backup generators are widely used, sometimes as the main source of
electricity. The hurricane also damaged the island’s existing air monitoring
network and the University of Puerto Rico’s observing facilities. We deployed
four lower-cost air quality monitors (Real-time Affordable Multi-Pollutant or
RAMP monitors) and a black carbon (BC) monitor in the San Juan Metro Area in
November 2017. The first month of data collected with the RAMPs showed high
sulfur dioxide (SO<sub>2</sub>) and carbon monoxide (CO) concentrations of
varying magnitudes each night. SO<sub>2</sub> and CO are strongly correlated (r<sup>2</sup>
>0.9) at two sites ~5 km apart (University of Puerto Rico and an
industrial area, Puerto Nuevo), suggesting a single source type. BC measured at
the UPR site is also well correlated with CO and SO<sub>2</sub>. While the
RAMPs are not certified as a federal equivalent method, the RAMP SO<sub>2</sub>
data suggest that the EPA’s daily 1-hour threshold for SO<sub>2</sub>
(75 ppb) was exceeded on almost 80% of the first 30 days of deployment
(November-December 2017). The widespread reliance on generators for regular
electric supply in the aftermath of Hurricane Maria appears to have increased
air pollution in San Juan