The Environmental Protection Agency just tightened standards for tiny, pervasive soot particles from construction sites, smokestacks, tailpipes, wildfires and other sources.

Why it matters: This form of air pollution is dangerous. It's linked to asthma, irregular heartbeats, bronchitis, even premature death in people with heart or lung disease, per the EPA.

• Environmental groups — a key Democratic political constituency — loudly cheered, calling it an important public health move.
• But business groups, citing steady improvements in air quality, say ratcheting down requirements again would throttle development and jobs.

State of play: The agency is imposing a new annualized exposure mandate for fine particulates of 9 micrograms per cubic meter (µg/m3), down from the current 12 µg/m3 requirement.

Zoom in: The agency estimates the rule will provide $46 billion in net health benefits in 2032, the earliest date that states must begin achieving the lower levels.

• These projected upsides in 2032 include up to 4,500 avoided premature deaths and 800,000 avoided cases of asthma symptoms.
• EPA says compliance costs are a tiny fraction of the benefit value. It rejects claims the rule hurts the economy, noting that since 2000, this pollution has fallen 42% while gross domestic product climbed 52%.

Yes, but: Many industries — petroleum, metals, mining, and forest and paper, to name just a few — allege dire economic outcomes from tougher mandates.

• A late 2023 letter to the White House warns of "permitting gridlock" and "no room" for further development — even climate-friendly infrastructure — in some areas.
• "For each level of increased stringency of the standards, the burdens on states and manufacturers increase exponentially," a suite of industry groups wrote.

The intrigue: This is among the most heavily lobbied EPA rules of the Biden era.

• Backers and critics held dozens of closed-door talks with White House and EPA staff to sway the outcome (check this "meetings" link).

Threat level: Multiple studies show people of color face higher exposure to fine particulates.

There have been improvements in lowering soot concentrations, but a significant number of places would not currently meet the new limits (see above).

• It's a broad national snapshot based on 361 monitoring sites, so your mileage may vary.

Yes, but: "EPA expects that 99% of U.S. counties will be able to meet the revised PM2.5 annual standard with actions already in place as of 2032," EPA said.

What we're watching: Potential litigation, and whether a potential Trump administration would seek to alter the rule, or stop defending it in court.

• When he was president, Trump officials decided not to lower the standards.