Planting trees is a popular strategy to help make cities “greener,” both literally and figuratively. But scientists have found a counterintuitive effect of urban vegetation: During heat waves, it can increase air pollution levels and the formation of ozone. Their study appears in ACS’ journalEnvironmental Science & Technology.

Previous research has shown that planting trees in cities can have multiple benefits, including storing carbon, controlling storm water and cooling areas off by providing shade. This has spurred efforts in cities across the U.S. and Europe to encourage the practice. However, it’s also known that trees and other plants release volatile organic compounds, or VOCs, that can interact with other substances and contribute to air pollution. And when it’s hot, plants release higher levels of VOCs. Galina Churkina and colleagues wanted to investigate what effects heat waves and urban vegetation might have on air pollution.

At the Maji Agricultural Reservoir in Wonju, Gangwond-do, South Korea, that someone is Tae Kwon Lee. Lee regularly jogs around the reservoir. One day he noticed large black birds completely covering the small island in the lake. The black birds were great cormorants, a type of large water bird, and the trees on the islet were completely covered in the birds’ feces. As time passed, Lee made another observation: the lake suffered a severe algal bloom.

Algal blooms deplete oxygen in lakes, produce toxins, and end up killing aquatic life in the lake. This sequence of events got Lee wondering: Did the bird feces cause or contribute to the algal bloom?

The study, just published in the journal Atmospheric Environment, points out that low hedges reduce the impact of pollution from vehicles in cityscapes where there are large buildings close to roads, far more effectively than taller trees. In some environments, trees actually make the pollution more concentrated depending on prevailing wind conditions and built-up configurations.

A study, published in Nature, has shown that laboratory tests of nitrogen oxide emissions from diesel vehicles significantly underestimate the real-world emissions by as much as 50 per cent.

The research, led by the International Council on Clean Transportation and Environmental Health Analytics, LLC., in collaboration with scientists at the University of York’s Stockholm Environment Institute (SEI); University of Colorado; and the International Institute for Applied Systems Analysis, examined 11 major vehicle markets representing more than 80% of new diesel vehicle sales in 2015. 

With the growing frequency and magnitude of toxic freshwater algal blooms becoming an increasingly worrisome public health concern, Carnegie scientists Jeff Ho and Anna Michalak, along with colleagues, have made new advances in understanding the drivers behind Lake Erie blooms and their implications for lake restoration. The work is published in two related studies.

Using data from NASA’s Landsat 5 instrument, the researchers generated new estimates of historical algal blooms in Lake Erie, more than doubling the number of years previously available for scientists to investigate, from 14 to 32. (This first study was published in Remote Sensing of Environment.) Exploring this new historical record, they discovered that decadal-scale cumulative phosphorous loading—that is the runoff that enters the waterway—helps to predict bloom size in addition to the effects from same-year phosphorus inputs. The work suggests that it may take up to a decade to reap the benefits of recently proposed nutrient loading reductions. (This second study was published in the Journal of Great Lakes Research.)

Ponds and lakes play a significant role in the global carbon cycle, and are often net emitters of carbon gases to the atmosphere.  However, the rate at which gases move across the air-water boundary is not well quantified, particularly for small ponds.

Analyses of environmental gases which previously required months of laboratory work can now be carried out rapidly in the field. A group of Eawag scientists have developed a portable mass spectrometer allowing on-site measurements – and a spin-off has been created to commercialize the new system.

What are the effects of volcanic gases accumulating in Lake Kivu in central Africa? How does the Rhine’s groundwater system function near Pratteln? What is the best way of controlling greenhouse gas emissions from a landfill in northeastern Switzerland? Answers to questions like these can be provided by a newly developed portable mass spectrometer – by the researchers named “miniRuedi” – which allows gas and water samples to be analysed on site and in real time. For example, the concentrations of different gases were determined at a landfill during a one-day measurement campaign. This study supports the optimisation measures to aerate the landfill in order to reduce the formation of methane, a strong greenhouse gas.

Researchers have discovered for the first time that a common marine sponge hosts bacteria that specialize in the production of toxic compounds nearly identical to man-made fire retardants, a finding that could help scientists better understand the human health implications of these common additives.

The new findings, by scientists at the Scripps Institution of Oceanography (SIO) at the University of California, San Diego, moved the research team a step closer to unraveling the mysteries of this powerful group of chemical compounds, known as polybrominated diphenyl ethers (PBDEs).

Man-made pollution in eastern China's cities worsens when less dust blows in from the Gobi Desert, according to a new study published May 11 in Nature Communications.

When it comes to removing very dilute concentrations of pollutants from water, existing separation methods tend to be energy- and chemical-intensive. Now, a new method developed at MIT could provide a selective alternative for removing even extremely low levels of unwanted compounds.