On April 29, 2015, the U.S. Geological Survey (USGS) reported five earthquakes in Oklahoma of magnitude 2.5 or greater—that is, tremors strong enough to be felt. The most powerful of these was a M4.1 earthquake 21 km (13 mi) west of the city of Perry in north-central Oklahoma. Based on recent evidence reported by the USGS, these earthquakes were almost certainly induced by human activity as a consequence of the injection of wastewater from oil and gas production into deep disposal wells. See also: Earthquake; Oil and gas field exploitation; Well

Although asphalt (also known as bitumen) is a naturally occurring substance found in deposits within the earth, it is also a by-product of petroleum processing. Almost all the bitumen used for asphalt pavement and roofs comes from petroleum refining and consists of hydrocarbon compounds that remain at the upper end (600°C or 1100°F) of the vacuum-distillation process. Because asphalt cannot be vacuum distilled, it has long been assumed that installed asphalt pavement and roofs do not emit hydrocarbon pollutants. Yet, according to a new report in the journal Science Advances (September 2020), asphalt pavements and roofs do, in fact, emit significant quantities of hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs), particularly in environmental conditions found on hot and sunny days. This is problematic, because some PAHs are mutagens, teratogens, carcinogens, or endocrine disruptors and therefore harmful to human health and the environment. Hydrocarbons may also act as precursors to air pollutants, because hydrocarbons can react with nitrogen oxides (NO_x) and sunlight to form ozone, a major constituent of smog. See also: Air pollution; Aromatic hydrocarbon; Asphalt and asphaltite; Environmental toxicology; Nitrogen oxides; Ozone; Pavement; Petroleum; Petroleum processing and refining; Petroleum products; Roof construction; Smog

Many questions concerning the sustainable production of biofuels have emerged over recent years in terms of land and water use, pollution from fertilizer and pest-control chemicals, greenhouse-gas production, net energy production, and whether enhanced land-use and climate benefits would result from simply planting trees and eschewing biofuels altogether. According to researchers reporting in the Proceedings of the National Academy of Sciences (September 2020), the answer depends, in part, on optimizing land-use policies and bioenergy production systems. Researchers have concluded that sustainable biofuels could make an important contribution toward reducing greenhouse-gas emissions and stabilizing the global climate if we produce bioethanol from biomass sources, such as perennial grasses, that are grown without affecting the carbon already stored in the ecosystem. See also: Biomass; Ethyl alcohol; Global climate change; Greenhouse effect; Land-use planning; Reforestation

Plastic is a ubiquitous and life-saving product, but it is also rapidly becoming a significant environmental problem. Globally, less than 10 percent of plastics are recycled, about 12 percent are incinerated, and the vast majority are disposed of in landfills or littered in the natural environment. Reasons for this low rate of recycling include the low cost of feedstocks (monomers) derived from oil; inexpensive landfill space; and the fact that some plastics, such as poly(vinyl chloride), low-density polyethylene, polypropylene, and polystyrene have chemical properties that make them difficult to recycle. See also: Petroleum products; Plastic waste pollution; Polymer; Polyolefin; Polystyrene; Polyvinyl resins

Mosquito repellents are natural and synthetic chemical compounds that are applied to skin, clothing, and sometimes home furnishings such as bed nets. For years, they have been an important defense against mosquito-borne diseases, such as Dengue fever, malaria, and West Nile virus, and most recently Zika virus. See also: Diptera; Insect diseases; Insecticide; Malaria; Mosquito: vector of disease; West Nile virus; Zika virus disease

Over the next 10 to 20 years, capturing carbon dioxide (CO₂)—a powerful greenhouse gas emitted from sources such as fossil-fuel-burning power plants, natural-gas processing plants, bioethanol plants, and cement plants—could become a significant method for mitigating climate change. Most of the captured CO₂ would probably be injected deep into the earth, a practice known as carbon capture and storage (CCS). The U.S. Department of Energy (DOE) estimates that the current cost to capture a ton of CO₂ is $60, which is cost prohibitive. With technological improvements, the DOE projects the cost to capture a ton of CO₂ could drop to a more affordable $40 in 10 years. See also: Carbon capture and storage; Carbon dioxide; Cement; Electric power generation; Global climate change; Greenhouse effect; Natural gas

If you think converting seawater to fuels that can power ships is a fantasy, think again. Researchers at the U.S. Naval Research Laboratory in Washington, D.C., have, in fact, accomplished this feat. In addition, the U.S. Navy has received a patent for an electrochemical device that removes carbon dioxide (CO₂) and hydrogen (H₂) gases from seawater, which together can be converted through a catalytic reaction to liquid hydrocarbon fuels that are similar to fossil fuels. Breakthrough technology aside, don’t expect to see U.S. Naval ships powered by fuels from seawater cruising the high seas anytime soon. Making significant quantities of this fuel requires processing a great deal of seawater, which, in turn, requires a large amount of electricity to drive the electrochemical process. Nevertheless, researchers expect efficiency improvements over the next 10 years to bring the concept closer to reality. See also: Carbon dioxide; Catalysis and catalysts; Electrochemical process; Fossil fuel; Hydrogen; Seawater

Due to their attractive properties, including high energy density and long cycle lives, lithium-ion batteries have become widely adopted in portable electronics and electric vehicles and continue to make inroads as renewable energy storage cells. However, as a raw material, lithium poses long-term economic and environmental sustainability concerns. These concerns include lithium's relatively high cost, looming scarcity, and negative environmental impacts from mining. As a potential alternative to lithium-ion batteries, researchers have been pursuing sodium-ion batteries (SIBs). Compared to lithium, sodium is significantly more abundant in Earth's crust, would be less expensive to obtain, and overall poses fewer environmental concerns. That said, sodium has proven far less tractable as a battery material. To address many of the issues that have stalled SIB advancement, researchers at Pusan National University in South Korea have developed new SIB anode materials. These new materials are efficient, are easily prepared, show high sodium-ion storage capacity, and have excellent cycle stability compared to their predecessors. The research team accordingly hopes that their technology can be used for large-scale production of sodium ion-based energy storage systems in the future. See also: Energy storage; Lithium; Mining; Sodium

Ethylene, CH₂=CH₂, the most-produced organic chemical in the world, is used to make hundreds of products. The major product is polyethylene, but other important ones include poly(vinyl chloride), polystyrene, antifreeze (ethylene glycol), adhesives, solvents, and detergents. See also: Adhesive; Detergent; Ethylene; Ethylene glycol; Polyolefin resins; Polystyrene resin; Polyvinyl resins; Renewable resources; Solvent

In recent years, researchers have made considerable progress toward producing renewable energy in the form of hydrogen fuel through the electrolysis of water. In the most basic electrolytic cell, an electric current drives a chemical reaction at two electrodes in contact with an electrolyte solution to split water (H₂O) into hydrogen (H₂) and oxygen (O₂). A more sophisticated photoelectrochemical cell under development, called an artificial leaf, splits water by using a silicon solar cell to absorb light and generate an electrical current and two electrocatalyst-coated surfaces to drive the same reaction. In all cases, efficient water splitting requires pure water to avoid damaging the electrodes. See also: Catalysis and catalysts; Electrochemistry; Electrolysis; Electrolyte; Hydrogen; Oxygen; Progress in developing an "artificial leaf" for hydrogen fuel generation; Solar cell; Water