| Total requests for May 2009: 1,144 |
| Unique requests | Total requests | Query | Documents returned |
| 11 | 12 | naaqs | 51,481 |
| 10 | 23 | nsps | 1,733 |
| 10 | 13 | NAAQS Table 681 573 | 2,427 |
| 5 | 8 | New Source Performance Standards 573 | 16,452 |
| 5 | 6 | clean air act | 7,327 |
| 4 | 8 | emergency generator | 670 |
| 4 | 7 | pm 2.5 | 21,908 |
| 4 | 6 | Method 300.1 | 17,301 |
| 4 | 6 | AP-42 | 1,711 |
| 4 | 5 | HAPs | 6,843 |
| 4 | 4 | Carbon monoxide | 5,750 |
| 3 | 6 | air pollution | 42,507 |
| 3 | 5 | nitrogen dioxide | 4,298 |
| 3 | 4 | permits 67 | 2,723 |
| 3 | 4 | mact | 4,096 |
| 3 | 4 | VOCs | 52,040 |
| 3 | 3 | attainment | 7,828 |
| 2 | 13 | design value | 6,453 |
| 2 | 8 | routine maintenance 25 681 | 110 |
| 2 | 6 | how can we reduce air pollution | 479 |
| 2 | 4 | state implementation plans 681 | 6,761 |
| 2 | 4 | startup shutdown malfunction | 914 |
| 2 | 4 | portland cement | 22,544 |
| 2 | 4 | particulate matter | 7,664 |
| 2 | 4 | new source | 6,604 |
| 2 | 4 | RICE | 24,965 |
| 2 | 3 | title V | 6,660 |
| 2 | 3 | nox | 91,420 |
| 2 | 3 | hydrocarbons | 3,127 |
| 2 | 3 | green book | 1,845 |
| 2 | 3 | EPA-453R-95-017 | 36 |
| 2 | 2 | wood stove | 796 |
| 2 | 2 | subpart IIII | 81 |
| 2 | 2 | psd | 2,779 |
| 2 | 2 | ozone depletion | 1,215 |
| 2 | 2 | oaqps | 20,326 |
| 2 | 2 | nsr | 3,130 |
| 2 | 2 | mold | 3,555 |
| 2 | 2 | mcls | 33 |
| 2 | 2 | fires | 11,605 |
| 2 | 2 | climate communities | 1,389 |
| 2 | 2 | cdx | 309 |
| 2 | 2 | casac | 550 |
| 2 | 2 | caaac | 510 |
| 2 | 2 | boiler mact | 720 |
| 2 | 2 | aqi 454 | 6,857 |
| 2 | 2 | TRI | 2,565 |
| 2 | 2 | RMP | 104 |
| 2 | 2 | Formaldehyde | 2,594 |
| 1 | 10 | PSD increase production exclusion | 337 |
| 1 | 9 | benzene air | 2,152 |
| 1 | 8 | emergency generator emissions | 581 |
| 1 | 8 | NSPS K | 10,660 |
| 1 | 7 | nsps wood stove | 99 |
| 1 | 7 | miscellaneousganic NESHAP ethanol plants | 78 |
| 1 | 7 | foia | 117 |
| 1 | 7 | endangerment | 12,527 |
| 1 | 7 | CERCLA | 94 |
| 1 | 6 | outdoor formaldehyde | 26,835 |
| 1 | 6 | indigo | 41 |
| 1 | 6 | equivalent diameter of stack | 1,057 |
| 1 | 5 | ssm plans | 234 |
| 1 | 5 | plan approval construction | 319 |
| 1 | 5 | photochemical smog | 20,798 |
| 1 | 5 | oil natural gas | 3,764 |
| 1 | 5 | ethiopia energy failure | 25,811 |
| 1 | 5 | cyanide | 450 |
| 1 | 5 | coal processing 8 | 42,218 |
| 1 | 5 | Vinyl bromide | 20,166 |
| 1 | 5 | MSW combustion 143 | 19,435 |
| 1 | 5 | Guideline on Air Quality Models Revised | 331 |
| 1 | 4 | washington county wisconsin | 567 |
| 1 | 4 | stockpiling engines | 4,002 |
| 1 | 4 | polluted air | 55,381 |
| 1 | 4 | part 60 | 5,904 |
| 1 | 4 | outdoor air | 551 |
| 1 | 4 | marcellus shale | 2,970 |
| 1 | 4 | in door pub clean air | 19,843 |
| 1 | 4 | federal major | 2,692 |
| 1 | 4 | ethanol plants | 987 |
| 1 | 4 | electric utility malfunction shutdown | 17 |
| 1 | 4 | criteria air pollution | 4,928 |
| 1 | 4 | coal sulfur dioxide scrubber bypass spare | 17 |
| 1 | 4 | benmap | 171 |
| 1 | 4 | NSPS index | 25,757 |
| 1 | 4 | NSPS Kb | 171,870 |
| 1 | 4 | CUE Cost | 19,840 |
| 1 | 4 | CAP summary | 252 |
| 1 | 4 | Ammonium Hydroxide chemical mixing plants exposure limits | 21,890 |
| 1 | 3 | wind tunnel audit | 27,388 |
| 1 | 3 | webinar training | 19 |
| 1 | 3 | volatileganic compounds | 2,822 |
| 1 | 3 | section 2021 of the Clean Air Act | 1,644 |
| 1 | 3 | power generators | 2,740 |
| 1 | 3 | portland cement MACT | 27,088 |
| 1 | 3 | plastic extrusion | 20 |
| 1 | 3 | photo | 136 |
| 1 | 3 | permit by rule | 28,910 |
| 1 | 3 | nitrogen oxides | 8,756 |
| 1 | 3 | nested | 45 |
| 1 | 3 | neighborhood electric vehicle | 1 |
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