| Acronym | Meaning |
| APT | Atomic Polar Tensor (in Ir Spectra Calcn.) |
| APT | Attached Proton Test |
| APTI | Air Pollution Training Institute |
| APTIC | Air Pollution Technical Information Center |
| APTT | Activated Partial Thromboplastin Time |
| APU | Acid Purification Unit (acid Recovery System) |
| APUD | Amine Precursor Uptake And Decarboxylation |
| APUHF | Approximately Projected Unrestricted Hartree-Fock |
| APUMPN | Approximately Projected Unrestricted Moeller-Plesset Nth-order |
| APW | Augmented Plane Wave |
| APWA | American Public Works Association |
| APWP | Apparent Polar Wander Path |
| APWR | Advanced Pressurized Water Reactor |
| APXPS | Appearance Potential X-ray Photoemission Spectroscopy |
| APYS | Auger-electron Partial Yield Spectroscopy |
| AQAM | Air Quality Assessment Model |
| AQCC | Air Quality Control Center |
| AQCC | Averaged Quadratic Coupled-cluster |
| AQCCT | Air Quality Criteria And Control Techniques |
| AQCDS | Air Quality Criteria Documents |
| AQCP | Air Quality Control Program |
| AQCR | Air Quality Control Region (US EPA) |
| AQCS | Analytical Quality Control Services |
| AQDHS | Air Quality Data Handling System |
| AQDM | Air Quality Display Model |
| AQF | American Quality Foundation |
| AQG | Air Quality Guideline |
| AQIRP | Auto/Oil Air Quality Improvement Research Program |
| AQL | Acceptable Quality Levels |
| AQLV | Air Quality Limit Values |
| AQM | Acenaphthenequinone Monoxime |
| AQM | Additive Quark Model |
| AQMA | Air Quality Maintenance Area |
| AQMD | Air Quality Management District |
| AQMP | Air Quality Management Plan |
| AQMWA | Air Quality And Waste Management Association |
| AQO | Average Quadrupole Orientation |
| AQPS | Air Quality Prediction System |
| AQRV | Air Quality Related Values |
| AQS | Air Quality Standard |
| AQS | Air Quality Subsystem (subsystem Of AIRS) |
| AQS | Ambient Quality Standard |
| AQSA | Anthraquinone-2-sulfonic Acid |
| AQSM | Air Quality Simulation Model |
| AQTAD | Air-Quality Technical Assistance Demonstration |
| AQUIRE | Aquatic Information Retrieval |
| AR | Androgen Receptorpar |
| AR | Angle Resolved (technique Prefix) |
| AR | Attributive Risk |
| ARA | Aggregate Risk Analysis |