An air quality standard, as a human activity, refers to the formally established regulatory limits on concentrations of specific atmospheric pollutants, derived through policy processes that integrate scientific risk assessment, exposure modeling, and socio-economic considerations. These standards define permissible ambient levels or emission thresholds for contaminants such as particulate matter, ozone, nitrogen oxides, and sulfur dioxide to protect human health and the environment. Their development and revision typically involve expert review of epidemiological and toxicological data, public consultation, and impact analyses, followed by legal codification and implementation through monitoring networks, compliance mechanisms, and enforcement actions.
Cities are rapidly becoming the defining residential space of human life. Over 55% of the global population lived in urban areas in 2018, a proportion projected to reach nearly 68% by 2050, according to the United Nations ...
Earth Sciences
Feb 27, 2026
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Fifteen years ago, Beijing's Liangma riverbanks would have been smog-choked and deserted in winter, but these days they are dotted with families and exercising pensioners most mornings.
Environment
Feb 17, 2026
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In North America and Europe, emissions of ozone precursors such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) declined by half between 2000 and 2018. However, the ozone content of the air—and thus the risk ...
Environment
Jan 29, 2026
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When I worked for the Environmental Protection Agency in the 2010s as an Obama administration appointee, I helped write and review dozens of regulations under the Clean Air Act. They included some groundbreaking rules, such ...
Environment
Jan 29, 2026
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The U.S. Environmental Protection Agency's effort to roll back federal particulate matter pollution standards will harm Michigan residents, particularly those who live near emitters such as manufacturing plants and refineries ...
Environment
Jan 28, 2026
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Worldwide, it ranks among the cities with the highest levels of air pollution—and it's located in the heart of Europe: Sarajevo, the capital of Bosnia and Herzegovina. Previously, the spatial distribution of air pollutants ...
Environment
Jan 22, 2026
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Air pollution across the UK dropped between 2015 and 2024, but dangerous levels are still reached too often, shows new research published in Environmental Science: Atmospheres.
Environment
Jul 15, 2025
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In 2003, several states and environmental groups sued the U.S. EPA for violating the Clean Air Act by not regulating emissions from new vehicles.
Environment
Jun 24, 2025
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A newly published study finds that California's Salton Sea emits hydrogen sulfide, a toxic and foul-smelling gas, at rates that regularly exceed the state's air quality standards. The presence of these emissions in communities ...
Earth Sciences
Jun 2, 2025
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The Los Angeles region has some of the most polluted air in the United States, failing to meet standards set by the Environmental Protection Agency for the last decade. Now, Caltech researchers have quantified the levels ...
Environment
May 21, 2025
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