Page ES-12, line 6: Although much more rare, regulations can also address nonanthropogenic PM emissions, such as pollutants.
Page ES-12, line 16: Why not use “EC” as the preferred term, and not “black carbon”?
Page ES-12, lines 22–23: Evaporative emissions (from vehicles, paints, solvents, and so on) are also substantial sources of organic carbon.
Page ES-12, lines 33–34: It is stated that transport of Asian PM to North America happens a few times per decade. How often is African PM transported to North America?
Page ES-15, bullet 1: These tools can be used to work on solutions, but they are more typically used for detecting problems.
Page ES-15, bullet 2, fifth point: Edit “Reduction in sulfate reduction.”
Page ES-18, bullet 1, last line: The last phrase of this sentence is vague.
Page ES-22, line 9: Edit “Other pollution issues other than.”
Pages ES-25 and ES-27: These figures are of limited use and are not cited in the text.
Page ES-28, line 32: “is required” should be “was required.”
Page ES-29, Table PQ7: It is not clear how “science assessments” and “state-of-knowledge assessments” differ.
Page ES-30, line 30: “Data is available” should be “Data are available.”
Page ES-32, line 7: “lease understood” should probably be “least understood.”
Page ES-32, line 20: “between pollutants” should be “among pollutants.”
Page ES-33, line 17: “data is” should be “data are.”
Page ES-34, line 15: Earlier, you describe “ultrafines” as 20 nm, but here you seem to be describing them as 1 nm.
Page ES-34, line 31: “data is” should be “data are.”
Page ES-35, line 22: Are you certain that you mean “prospective” here?
Page ES-35, line 25: It should read “studies including data.”