Atreyee Bhattacharya

Nitrous oxide pollution from aircraft to increase by 2050

The transportation industry is not only one of the biggest sources of air pollution and a significant player in greenhouse gas–induced global warming, but, as a new study shows, the industry could also be responsible for episodes of ozone (O3 ) pollution, particularly over the United States and northern Europe. Combustion of fuel in cars, shipping vessels, and low-flying aircraft produce nitrogen oxides (NOx), which not only decrease the lifetime of greenhouse gases such as methane but also react with other molecules in the atmosphere to form tropospheric O3, another, more lethal, air pollutant. Hauglustaine and Koff used a global three-dimensional chemistry-climate model to investigate how different components of the transportation industry—cars, ships, and low-flying aircraft—would contribute to NOx pollution over the next few decades under several projected emission scenarios. They found that as road transportation stagnates or even declines due to stricter regulations and congestion, NOx emissions from cars will decrease over time. However, aircraft will increase in number and could contribute between 25% and 48% of NOx emissions, which will be most severe over the United States and Europe—two regions with the highest growth rate in commercial aviation.

New model to estimate water in the Earth's mantle

The Earths mantle could be holding as much water as the ocean and atmosphere combined—but in the form of defects in dry minerals, such as olivine, that make up a large fraction of the mantle. Water in mantle minerals weakens chemical bonds, affecting physical and chemical properties of the mantle, particularly viscosity and electrical conductivity. Scientists continue to debate not just the amount of water but also its distribution in the mantle. Seismic velocity profiles, typically used to map the water content of the mantle, are, in fact, not sensitive to the amount of water. An increase of 1% by weight of water in mantle minerals, i.e., from “dry” to “very wet” conditions, reduces seismic velocities by at most 1%, which is often below the detection limit. On the other hand, an increase in water content by only 0.01%, from “dry” to “damp” conditions increases electrical conductivity in mantle minerals by an order of magnitude or more, making electrical conductivity a more sensitive tool to estimate the water content of mantle minerals.

Earthquake in Chile triggers tremors and slips in Mexico

Scientists recently observed that large earthquakes often trigger tremors in places far away, sometimes thousands of kilometers, from the epicenter. In a new study, researchers have now shown that a major earthquake in Chile in 2010 also could have triggered “slow slips”—events during which large parts of continents move undetected, without leaving any trail in seismograms. Zigone et al. show that the Maule earthquake in Chile (Mw 8.8) on 27 February 2010 generated surface waves (S waves) that within hours induced tremors in the Guerero region of Mexico. They also observed that GPS stations in the region started moving southward coincident with the arrival times of the S waves and the starting of the seismic tremors. The tremors and the southward movement of GPS stations continued for several months following the earthquake.

The random walk of tracers through river catchments

River catchments play critical roles in regional economies and in the global economy. In addition, rivers carry large volumes of nutrients, pollutants, and several other forms of tracers into the ocean. An intricate system of pathways and channels, both on the surface and in the subsurface of catchments, allows rivers to carry large volumes of tracers. However, scientists do not yet fully understand how pollutants and other tracers travel through the intricate web of channels in the catchment areas of rivers. In a new study, Cvetkovic et al show that the travel path of tracers through channels can be modeled as a random walk, which is mathematically similar to the path an animal would trace when foraging. Previous studies have applied the random walk approach to understand the behavior of fluids flowing through aquifers and soils but not to model the transport mechanism of tracers that travel passively with water flowing through catchments.

Carbon dioxide drove climate change during longest interglacial

Known as the marine isotope stage 11 (MIS 11), the interglacial period that occurred from approximately 425,000 years ago to approximately 375,000 years ago was the longest and possibly the warmest interglacial in the past 500,000 years. Because the orbital configurations, atmospheric greenhouse gas concentrations, climate, and faunal characteristics during MIS 11 closely resemble those of the past 5000 years, paleoclimatologists use MIS 11 as a geological analogue of the present and the near future. Several high- resolution records document almost all aspects of terrestrial and marine climate through MIS 11. However, there is neither a clear understanding about how climatic parameters such as atmospheric carbon dioxide (CO2), sea surface temperature, the isotopic makeup of carbon in marine and terrestrial reservoirs, and annual air temperature interact, nor a consensus regarding the major drivers of climate change during this interval.

Forest fires may cause cooling in boreal Canada

As climate in North America continues to become warmer and drier through the 21st century, a new study finds that fire may be playing an increasingly important role in shaping the climate of the boreal regions of Canada. Forest fires change the amount of shortwave radiation absorbed by Earths surface by reducing vegetation cover and changing the composition of plant species, thereby changing the reflectivity of the surface (albedo). Fires also affect other ecosystem processes and increase aerosol (particularly soot) emission and deposition, all of which alter regional climate through a series of feedbacks mechanisms. Jin et al. used satellite observations of surface albedo from 2000 to 2011 and fire perimeter data since 1970 to study how forest fires affect surface albedo and associated shortwave radiation at the surface, across forests in boreal Canada.

Turbulent forces within river plumes affect spread

When rivers drain into oceans through narrow mouths, hydraulic forces squeeze the river water into buoyant plumes that are clearly visible in satellite images. Worldwide, river plumes not only disperse freshwater, sediments, and nutrients but also spread pollutants and organisms from estuaries into the open ocean. In the United States, the Columbia River—the largest river by volume draining into the Pacific Ocean from North America—generates a plume at its mouth that transports juvenile salmon and other fish into the ocean. Clearly, the behavior and spread of river plumes, such as the Columbia River plume, affect the nations fishing industry as well as the global economy.

The pros and cons of trading water: A case study in Australia

Water is a commodity, and water rights can be freely traded in an open market. Proponents of the free market approach argue that it leads to the most efficient allocation of water resources, as it would for any other commodity. However, unlike some commodities, water is critical for human life, for many human activities, and as an environmental resource. When such an essential commodity becomes scarce, as frequently happens in Australia, which is prone to sudden and dramatic droughts, severe problems can occur quickly. In Australias Murray Darling Basin, the countrys largest agricultural region, the government had historically controlled the distribution of water rights. However, under these controls, a selected few controlled a large share of the water. To resolve this problem of overallocation, a free market approach was put in place in the early 1990s.

Water crises—a new approach

Water crises are one the biggest challenges facing humanity in the 21st century. But what exactly is the nature of these crises? Scientists investigated the underlying causes driving water scarcity in 22 of the best studied cases across India, China, South America, Russia, and Australia using a quantitative technique that breaks down exhaustive case studies into measurable parameters. Srinivasan et al. show that in spite of the numerous ways in which humans interact with fresh water, each shortage or crisis is driven by one or more of eight underlying causes—which can be grouped into six “syndromes.” The authors found that just as declining natural supply can drive water shortages, so can human consumption or lack of proper policies.

In California, 5 decades of decreasing emissions

Volatile organic compounds (VOCs), which are emitted by vehicles and are a leading source of air pollution, have been on the decline in Los Angeles, Calif., one of the densest and most poorly ventilated cities in the United States, a new study finds. Comparing detailed measurements from two aircraft campaigns in the Los Angeles basin in 2002 and 2010, Warneke et al. found that the VOC concentrations in the regions atmosphere declined significantly during those 8 years. Using data from literature statistics and a monitoring network, the authors further show that in the Los Angeles basin, concentrations of VOCs and carbon monoxide (CO) have declined by 2 orders of magnitude compared to the 1960s—a reduction of 7.5% every year since the 1960s in spite of the fact that the sale of fuels has increased threefold during the same interval of time.