<p class="ingestion featured-caption">The Columbus skyline.Carol Highsmith/Getty Images</p><ul class="summary-list"><li>IQAir's air quality report ranked the world's most and least polluted areas.</li><li>The report revealed 92.5% of countries and only 9% of cities met WHO's PM2.5 guidelines in 2023.</li></ul><p>Swiss company IQAir ranked the most and least polluted countries and cities in the world in a recent <a target="_blank" rel href="https://www.businessinsider.com/global-air-quality-report-finland-iceland-canada-wildfires-2024-3"><u>air quality report.</u></a></p><p>Unlike some other rankings, IQAir, which sells air-purification products, based its report entirely on PM2.5 levels, a type of small-particle pollution that has been linked to heart and lung issues.</p><p>According to the report, <a target="_blank" href="https://www.businessinsider.com/global-air-quality-report-finland-iceland-canada-wildfires-2024-3">92.5% of countries have too much PM2.5.</a> And only 9% of cities surveyed achieved WHO's guidelines of acceptable PM2.5 levels in 2023.</p><p>In a statement sent to Business Insider, the organization said it used publicly available data, including from low-cost sensors and government-operated regulation stations, to monitor PM2.5 levels in 2,933 US cities between January and December of 2023.</p><p>Cities in Arizona, Nevada, and Colorado were among the <a target="_blank" href="https://www.businessinsider.com/cities-united-states-cleanest-air-least-pollution-2024-4">least polluted</a> in the US.</p><p>Meanwhile, cities in California, Georgia, and Iowa were named the most polluted, as shown in the below ranking.</p><p><em>Only cities with populations over 50,000 were included in this ranking.</em></p>