Modesty has not exactly been the hallmark of the Obama administration’s Environmental Protection Agency. In 2009, it declared that carbon dioxide — the air we exhale — is a “pollutant,” and thus falls under the Clean Air Act.

That’s why we should worry about the EPA’s upcoming decision about whether to change the regulations that govern “particulate matter” — a category that includes such nefarious toxins as farm dust. A 2010 draft policy assessment by the agency’s staff suggested that the EPA should impose massive burdens on much of the country.

The EPA is expected to release a final version of the report soon, an official policy proposal around August, and a final policy later in the year. House Republicans are trying to block additional regulations, but the Democratic Senate and President Obama could prove obstacles to fixing this problem through legislation.

Some background: In 1990, the Clean Air Act mandated the creation of a network of air-quality monitors throughout the country. Today, about 10 percent of counties have monitors that measure “PM10,” which includes both “fine” and “coarse” particulate matter. Fine particulate matter is created whenever vehicles emit exhaust fumes, or an individual smokes a cigarette; coarse matter is created whenever wind sweeps “fugitive dust” into the air on a farm, or a car kicks up dirt on an unpaved road.

The EPA has long regulated PM10, but it exempted farm dust from those regulations until it revised its standards in 2006. Now, if a monitored area consistently exceeds the EPA’s PM10 limits, it is designated a “non-attainment area” and forced to submit a plan for lowering its pollution levels.

The details are complicated, but the bottom line is that according to various studies, short-term spikes in PM10 levels cause cardiovascular and respiratory problems. However, this increase is slight — to the point that it’s difficult to detect statistically — and it shows up primarily (critics say exclusively) in urban areas. And, oddly, researchers haven’t been able to find a similar link between these problems and long-term exposure to this kind of dust.

Under the current policy, the permitted level of PM10 is 150 micrograms per cubic meter, and areas are allowed to exceed that level one day per year. About 14 percent of monitored counties fail to meet this standard. When classified as non-attainment areas, such localities might promise to build barriers to keep dust from blowing in the wind, discourage the use of wood-burning stoves, instruct farmers to change their practices, or mandate higher efficiency standards for cars.

The 2010 EPA report offers two ways of looking at this situation. The first is to emphasize the uncertainty of the science and conclude that the status quo, which has succeeded in reducing PM10 levels nationwide, is working. The second, however, is to note that the studies are fairly consistent in finding at least a small health effect — including in cities that meet the current standard, which implies that the standard could use some adjustments.

Based on the second analysis, the report proposes decreasing the level of PM10 that’s permitted to 85 micrograms per cubic meter, while increasing the number of days each area is allowed to exceed it to 2 percent (about seven per year). The EPA claims that this standard is about as protective as the current one.

This setup does have some advantages. Three of the urban areas in which studies found health effects from coarse particulate matter — Detroit, Chicago, and Pittsburgh — meet the current standard, but would have to make improvements under the proposed one, according to the report. Also, of people living in monitored areas, the proportion living in areas that violate the standard would fall from 26 to 19 percent under the revision.