Which of the following is true regarding secondary pollutants?

The statement that secondary pollutants form through chemical reactions in the atmosphere is accurate. Secondary pollutants are not emitted directly from a source; instead, they develop when primary pollutants, which are released directly, react with other substances in the atmosphere. This can occur through various chemical reactions involving sunlight, water, and other atmospheric constituents. A common example of a secondary pollutant is ozone, which forms when sunlight reacts with pollutants like volatile organic compounds (VOCs) and nitrogen oxides.

Other options do not accurately describe secondary pollutants. They are not inherently harmful upon direct release since they are not released directly at all. Additionally, secondary pollutants can originate from both natural and anthropogenic (human-made) processes, rather than just from natural processes. Furthermore, secondary pollutants can be just as harmful, if not more so, than primary pollutants, challenging the idea that they are always less dangerous.