| Acronym | Meaning |
 | ARM | Anhysteretic Remanent Magnetization |
 | ARM | Area Radiation Monitoring |
 | ARM | Atmospheric Radiation Measurement |
 | ARM | Atomic Resolution Microscope |
 | ARMA | Autoregressive-moving Average Stochastic Model |
 | ARMAX | Autoregressive Moving Average Exogenous |
 | ARMI | Analytical Reference Materials International |
 | ARMS | Angle-resolved Mass Spectrometry |
 | ARNT | Aryl Hydrocarbon Receptor Nuclear Translocator |
 | ARO | Analytical Radial Orbital |
 | ARP | Adiabatic Rapid Passage |
 | ARP | Angle-resolved Photoemission |
 | ARPA | Advanced Research Projects Agency |
 | ARPA | Augmented Random Phase Approximation |
 | ARPEFS | Angle-resolved Photoemission Extended Fine Structure |
 | ARPES | Angle-resolved Photoelectron Spectroscopy |
 | ARPKD | Autosomal Recessive Polycystic Kidney Disease |
 | ARPS | Angle-resolved Photoelectron Spectroscopy |
 | ARPUS | Angle-resolved Ultraviolet Photoelectron Spectroscopy |
 | ARROW | Anti-resonant Reflecting Optical Waveguide |
 | ARRP | Acid Rain Research Program |
 | ARRP | Ammonia Removal And Recovery Process |
 | ARRPA | Air Resources Regional Pollution Assessment Model |
 | ARS | Agricultural Research Service (US Dept. Of Agriculture) |
 | ARS | Autonomously Replicating Sequence |
 | ARSCF | Approximate Relativistic SCF |
 | ARSCFC | Approximate Relativistic SCF (with) Corrections |
 | ARSPIPES | Angle Resolved Spin Polarised Inverse Photo Emission Spectroscopy |
 | ART | Advanced Recycling Technologies |
 | ART | Absolute Rate Theory |
 | ART | Asphalt Residual Treatment |
 | ART | Atom Relay Transistor |
 | ARUPS | Angle-resolved Ultraviolet Photoelectron Spectroscopy |
 | ARXAS | Angle-resolved X-ray Absorption |
 | ARXPD | Angle Resolved X-ray Photoelectron Diffraction |
 | ARXPS | Angular Resolved X-ray Photoelectron Spectroscopy |
 | AS | Auger Spectroscopy |
 | AS | Absorption Spectroscopy |
 | AS | Activated Sludge |
 | AS | Air Stripping |
 | AS-PCR | Allele-specific Polymerase Chain Reaction |
 | ASA | American Society Of Agronomy |
 | ASA | Acrylonitrile-styrene-acrylate Terpolymer |
 | ASA | Alkenylsuccinic Anhydride |
 | ASA | Alternancy Symmetry Adapted (method For Spin-independent Hamiltonians For Alternant Hydrocarbons) |
 | ASA | At. Sphere Approxn. |
 | ASAE | Alkali-sulfite-anthraquinone-ethanol (pulping Process) |
 | ASAE | American Society Of Agricultural Engineers |
 | ASAS | Advanced Solid State Array Spectrometer |
 | ASASP | Active Scattering Aerosol Spectrometer Probe |