【推荐1】People often recommend planting trees to make cities greener, cleaner and healthier. But during heat waves, city trees can actually increase air pollution. Indeed, a new study finds that up to 60% of the ozone (臭氧) in a city’s air on hot days may have its origin in chemicals released by trees.

City trees offer a host of benefits. They provide cooling shade, absorb carbon dioxide, and also release oxygen into the air. But oxygen is far from the only gas that trees and certain other green plants release into the air. One of these chemicals is a hydrocarbon(碳氢化合物) that can react with burning pollutants, such as nitrogen oxides (氮氧化合物). The result is the formation of ozone which can cause airway diseases.

Galina Churkina works in Germany at Humboldt University of Berlin. She and her team wanted to explore how much chemicals released by trees could affect city air. To do this, the researchers turned to a computer. They asked it to model the likely reactions between plant chemicals and nitrogen oxides in air throughout the Berlin city area. To do that, the researchers fed in local weather data for two summers. One was 2006, when there was a heat wave. The other was 2014, when temperatures were mild.

An average daily high there in summer tends to be at roughly 25℃. On such a day, chemicals released by area greenery would likely have contributed to making about 6 to 20 percent of the ozone in the city’s air. But during a heat wave, when temperatures are more than 30℃ , tree-chemical emissions (发出物) are also high. As a result, they are now likely to be responsible for up to 60 percent of the ozone in air.

Churkina says her team was not surprised to see the contrary relationship between plants and pollution. The results, Churkina says, suggest city tree-planting programs should not ignore the role this greenery may play in bad summer air pollution. Adding more trees will improve quality of life only if those cities also undertake plans to sharply cut vehicle pollution (汽车污染).

【推荐2】How Young Americans Spend Their Money

Young people have always puzzled their elders. Today’s youngsters are no different; indeed, they are confusing. They have thin wallets and expensive tastes. They prize convenience and a social conscience. They want shopping to be personal.     1     As they start spending in earnest, brands are trying to understand what these walking paradoxes with conflicting features want and how they shop. The answers will define the next era of consumerism.

Their absolute numbers are impressive. The European Union is home to nearly 125m people between the ages of ten (the youngest will become consumers in the next few years) and 34. America has another 110m of these Gen-Zs and millennials, a third of the population. The annual spending of households headed by American Gen-Zs and millennials hit $2.7trn in 2021, around 30% of the total.

    2     Forrester, a market-research firm, found that most users of “buy now, pay later” apps are around 20. Megan Scott, a 20-year-old student from London, speaks for many of her peers by admitting that, when shopping, she has no self-control—until the bill arrives.

The light-speed online world also appears to have lowered tolerances for long delivery times. A study by Salesforce, a business-software giant, found that Gen-Z Americans, who prefer to use their phones to pay for shopping, are the likeliest of all age groups to want their groceries delivered within an hour.     3    

The Internet has also changed how the young discover brands. Print, billboard or TV advertising has given way to social media. Instagram, part of Meta’s empire, and TikTok, a Chinese-owned app, are where the young look for inspiration, particularly for goods where looks matter such as fashion, beauty and sportswear.     4     Such apps are increasingly adding features that allow users to shop without ever leaving the platform. According to McKinsey, six in ten Americans under the age of 25 had completed a purchase on a social-media site.

【推荐3】Most people often listen to music near bedtime to relax. But can that actually cause your sleep to suffer? When sleep researcher Michael Scullin realized that he was waking in the middle of the night with a song stuck in his head, he saw an opportunity. He decided to study a rarely-explored mechanism (机制): how music — and particularly songs stuck in one’s head — might affect sleep patterns.

Scullin said, “Everyone knows that music listening feels good. Young adults routinely listen to music near bedtime. Thus, they are easy to experience ‘earworms’ — involuntary musical imagery. It’s a condition where a song or tune will replay over and over in our mind, and our brains continue to process music even when none is playing, including apparently while we are asleep.”

Scullin’s recent study included a survey and a laboratory experiment. The survey involved 209 participants who completed a series of surveys on sleep quality, music listening habits and earworm frequency. In the 50-participant experimental study, the research team played three popular and catchy songs before bedtime. They randomly assigned participants to listen to the original versions of those songs or the instrumental versions of the songs. And then they used polysomnography (PSG) — a comprehensive test of sleep — to record the participants’ brain waves, heart rates, breathing and more while they were sleeping.

The study showed that people who experience earworms regularly at night are six times as likely to have poor sleep quality as people who rarely experience earworms. “Almost everyone thought music improves sleep but we have found that those who listen to more music sleep worse,” Scullin said. “What’s really surprising is that instrumental music leads to worse sleep quality, including greater difficulty falling asleep, more nighttime awakenings, and more time in light stages of sleep. And instrumental music leads to about twice as many earworms.”

To get rid of an earworm, engaging in cognitive (认知的) activity — fully focusing on a task, helps to distract your brain from earworms if you don’t want to totally quit your music hobbies (listening to less music before bed is still encouraged). A previous study found that participants who spent five minutes writing down upcoming tasks before bed slept better.