Department of Environmental Science, Policy, and Management

In the troposphere, the heterogeneous lifetime of an organic molecule in an aerosol exposed to hydroxyl radicals (OH) is thought to be weeks, which is orders of magnitude slower than the analogous gas phase reactions (hours). Here, we report an unexpectedly large acceleration in the effective heterogeneous OH reaction rate in the presence of NO. This 10-50 fold acceleration originates from free radical chain reactions, propagated by alkoxy radicals that form inside the aerosol by the reaction of NO with peroxy radicals, which do not appear to produce chain terminating products (e.g., alkyl nitrates), unlike gas phase mechanisms. A kinetic model, constrained by experiments, suggests that in polluted regions heterogeneous oxidation plays a much more prominent role in the daily chemical evolution of organic aerosol than previously believed.

Over the last decades, air pollution emissions have decreased substantially; however, inequities in air pollution persist. We evaluate county-level racial/ethnic and socioeconomic disparities in emissions changes from six air pollution source sectors (industry [SO2], energy [SO2, NOx], agriculture [NH3], commercial [NOx], residential [particulate organic carbon], and on-road transportation [NOx]) in the contiguous United States during the 40 years following the Clean Air Act (CAA) enactment (1970-2010). We calculate relative emission changes and examine the differential changes given county demographics using hierarchical nested models. The results show racial/ethnic disparities, particularly in the industry and energy generation source sectors. We also find that median family income is a driver of variation in relative emissions changes in all sectors—counties with median family income >$75 K vs. less generally experience larger relative declines in industry, energy, transportation, residential, and commercial-related emissions. Emissions from most air pollution source sectors have, on a national level, decreased following the United States CAA. In this work, we show that the relative reductions in emissions varied across racial/ethnic and socioeconomic groups.

Microbes drive the biogeochemical cycles of earth systems, yet the long-standing goal of linking emerging genomic information, microbial traits, mechanistic ecosystem models, and projections under climate change has remained elusive despite a wealth of emerging genomic information. Here we developed a general genome-to-ecosystem (G2E) framework for integrating genome-inferred microbial kinetic traits into mechanistic models of terrestrial ecosystems and applied it at a well-studied Arctic wetland by benchmarking predictions against observed greenhouse gas emissions. We found variation in genome-inferred microbial kinetic traits resulted in large differences in simulated annual methane emissions, quantitatively demonstrating that the genomically observable variations in microbial capacity are consequential for ecosystem functioning. Applying microbial community-aggregated traits via genome relative-abundance-weighting gave better methane emissions predictions (i.e., up to 54% decrease in bias) compared to ignoring the observed abundances, highlighting the value of combined trait inferences and abundances. This work provides an example of integrating microbial functional trait-based genomics, mechanistic and pragmatic trait parameterizations of diverse microbial metabolisms, and mechanistic ecosystem modeling. The generalizable G2E framework will enable the use of abundant microbial metagenomics data to improve predictions of microbial interactions in many complex systems, including oceanic microbiomes.

Published scientific evidence shows that climate change caused by greenhouse gases from human activities endangers natural ecosystems around the world and in the United States, including in U.S. national parks, as shown in the latest report of the Intergovernmental Panel on Climate Change (IPCC 2022). The scientific evidence shows that the emissions of greenhouse gases from human activities that cause climate change endanger the public health and public welfare of current and future generations. This strongly supports maintaining the endangerment finding of the U.S. Environmental Protection Agency (US EPA 2009).

The Munții Făgăraș range in the southern Carpathian Mountains, Romania, harbors expanses of primary forest and high biodiversity, for which the European Union designated the area as a Natura 2000 site. Local initiatives seek to conserve Făgăraș ecosystems and services through its protection as the proposed Parcul Național Făgăraș, which would be one of the most extensive national parks in continental Europe. Uncontrolled logging poses an immediate threat. At the same time, climate change, caused by carbon dioxide emissions from power plants, motor vehicles, deforestation, and other human sources, threatens ecosystem integrity. Făgăraș forests naturally help prevent climate change by storing carbon. To assist long-term conservation of Făgăraș ecosystems, this climate change assessment presents locally specific scientific information on climate change, ecological impacts, risks, and the magnitude of forest carbon and its ecosystem service. Climate change increased annual average temperature of the proposed national park 1.5 ± 0.2ºC from 1901 to 2022, an increase that was statistically significant and higher than the global average. Precipitation showed no statistically significant long-term trend. Observed ecological changes detected in Europe and attributed by published scientific research to anthropogenic climate change include extirpations (local disappearances) of plant and animal species, upslope biome shifts, loss of bumble bee species, and warming of lake waters. Continued climate change under the highest greenhouse gas emissions scenario of the Intergovernmental Panel on Climate Change could increase annual average temperature of the proposed park area up to 6.4 ± 2.0ºC above the 1901-1910 average by 2100. Cutting emissions to meet the Paris Agreement goal globally could limit that projected local heating more than half. Under the highest emissions scenario, climate change could reduce total annual precipitation of the proposed park area 8 ± 4% below the 1901-1910 average by 2100. Meeting the Paris Agreement goal could result in precipitation at or slightly above the 1901-1910 average. Published research indicates that continued climate change could increase numerous risks to Făgăraș ecosystems, including biome shifts, tree mortality of European beech (Fagus sylvatica), silver fir (Abies alba), and Norway spruce (Picea abies), wildfire in an ecosystem where fire is unnatural, and range shifts of mammals. Forests in the proposed national park store 20 ± 9 million tons of carbon in aboveground biomass at densities up to 250 tons per hectare. The proposed Parcul Național Făgăraș could prevent this carbon from contributing to climate change, providing an ecosystem service equivalent to one year of emissions of 20 ± 9 million Romanians, the population of the entire country.