| P | Phosphorus |
| P2 | Pollution prevention |
| P2 Allowable Discharge | Pollution Prevention Allowable Discharge |
| Pa | Pascal; Permitting authority; Preliminary assessment; Privacy Act |
| PAC | Powdered activated carbon |
| PACE | Property assessed clean energy |
| PACs | Polycyclic aromatic compounds (*) |
| PADD | Petroleum Administration for Defense District |
| PAG | Protective action guide |
| PAGE | Poly Acrylamide Gel Electrophoresis |
| PAH | Phenanthrene; Polyaromatic hydrocarbon |
| PAHs | Polycyclic aromatic hydrocarbons |
| PAI | Pesticide active ingredient |
| PAI Manufacturing Process Unit | Pesticide active ingredient manufacturing process unit |
| PAMS | Photochemical assessment monitoring station |
| PAR | Photosynthetically active radiation |
| PART | Performance assessment rating tool |
| Partially Soluble HAP | Partially soluble hazardous air pollutant |
| Participating PRP | Participating potentially responsible party |
| Particle System Loss | Fugitive emission |
| Particulate HAP Transfer | Particulate hazardous air pollutant transfer |
| PA/SI | Preliminary assessment and site inspection; Preliminary Assessment/Site Inspection |
| Pb | Lead |
| PBBs | Polybrominated biphenyls (0.1); Polybrominated diphenyls |
| PBD-47 | 2,2',4,4'-Tetrabromodiphenyl Ether |
| PBDD | Polybrominated Dibenzo-p-Dioxin |
| PBDE | Polybrominated diphenyl ethers |
| PBF | Public benefit fund; Public benefits funds |
| PBFs for Clean Energy Supply | Public benefit funds for clean energy supply |
| PBFs for Energy Efficiency | Public benefit funds for energy efficiency |
| PBL | Planetary boundary layer; PowerBuilder library |
| PBMS | Performance based measurement system |
| PBPK Model | Physiologically based pharmacokinetic model |
| PBPK modeling | Physiologically-based pharmacokinetic modeling |
| PBT | Persistent bioaccumulative and toxic (PBT contaminants) |
| PBT Chemicals | Persistent bioaccumulative and toxic chemicals |
| PC | Personal Computer |
| PC Boiler | Pulverized coal boiler |
| PC Code | Pesticide chemical code |
| PCA | Principle components analysis |
| PCAL | Primary calibration standard |
| PCBs | Polychlorinated biphenyls |
| PCC | Portland cement concrete |
| PCD | Programmed cell death |
| PCDD | Polychlorinated Dibenzo-p-Dioxins |
| PCDF | Polychlorinated dibenzofurans |
| PCE | Perchloroethylene; Pollution control equipment |
| PCE (Blood) | Polychromatic erythrocyte |
| PCE or PERC | Tetrachloroethylene |
| pCi | Picocurie |
| pCi/L | Picocurie per liter; Picocuries per liter |
| PCM | Phase contrast microscopy |
| PCMe | PCM-equivalent |
| PCO | Pest control operator |
| PCP | Personal care product |
| PCR | Polymerase chain reaction |
| PCR Cycle | Photosynthetic carbon reduction cycle |
| PCR Method | Polymerase chain reaction method |
| PCR Technique | Polymerase chain reaction technique |
| PCR Technology | Rapid polymerase chain reaction technology |
| PCS | Permit compliance system; Personal communications service |
| PCW | Post-consumer waste |
| PCWP Manufacturing Facility | Plywood and composite wood products manufacturing facility |
| PD | Program description |
| PDF | Portable document file; Portable Document Format; Probability density function; Probability distribution function |
| PDMS | Pesticide Document Management System |
| PDMS Bibliography | Pesticide Document Management System bibliography |
| PDO | Pacific Decadal Oscillation |
| PDP | Principal display panel |
| PDS | Primary dilution standard |
| PE | Performance evaluation sample; Period emission table; Polyethylene; Program element |
| PEC | Probable effects concentration |
| PEL | Permissible exposure limit; Picture element; Probable effects level |
| PELs | Permissible exposure limit |
| PEM | Polymer electrolyte membrane |
| PEMS | Portable emission measurement system; Predictive emission monitoring system |
| Pending DTC | Pending diagnostic trouble code |
| PERL | Practical extraction and report language |
| PERM | Preliminary environmental review memorandum |
| Permanent DTC | Permanent diagnostic trouble code |
| Permanently Closed Container | Container |
| Permanganate-Based ISCO | Permanganate-based in-situ chemical oxidation |
| Peroxide and Iron ISCO | Peroxide and iron in-situ chemical oxidation |
| Persulfate ISCO | Persulfate in-situ chemical oxidation |
| PES | Payment for ecosystem services |
| PET | Poly(ethylene Terephthalate) |
| PET Manufacture Using Dimethyl Terephthalate | Poly(ethylene terephthalate) manufacture using dimethyl terephthalate |
| PET Manufacture Using Terephthalic Acid | Poly(ethylene terephthalate) manufacture using terephthalic acid |
| PET Resin | Poly(ethylene terephthalate) resin |
| PETE | Polyethylene terephthalate; Polyethylene terepthalate |
| Petroleum UST System | Petroleum underground storage tank system |
| PFAA | Perfluorinated alkyl acids and salts |
| PFAC | Perfluoroalkyl carboxylate |
| PFAS | Per-and polyfluoroalkyl substances; Perfluoroalkyl sulfonate |
| PFAS Pollutant Category | Per- and polyfluoroalkyl substances pollutant category |
| PFBS | Perfluorobutane sulfonic acid |
| PFC | Perfluorinated chemical; Perfluorocarbon |
| PFC Exposure | Perfluorinated chemical exposure |
| PFC Release | Perfluorinated chemical release |
| PFCs | Perfluorocarbon |
| PFDE | Particle free diesel exhaust |
| PFE | Percentage frequency effect |
| PFGE | Pulse field gel electrophoresis |
| PFOA | Perfluorooctanoic acid |
| PFOS | Perfluorooctyl sulfonate |
| PFPR Manufacturer | Pesticide formulating packaging and repackaging manufacturer |
| PFT | Pulmonary function |
| pg | Microgram |
| pg/L | Micrograms per liter |
| PGVP | EPA protocol gas verification program |
| PHDD | Polyhalogenated Dibenzo-p-Dioxins |
| PHDF | Polyhalogenated dibenzofurans |
| PHEV | Plug-in hybrid electric vehicle |
| PHT | Phthalates |
| PI | Plasticity index; Preliminary injunction; Principal investigator |
| PIC | Incomplete combustion product; Person in charge |
| PICC | Prescribed interexchange charge |
| PICs | Products of incomplete combustion |
| PII | Privacy/Personally Identifiable Information |
| PILS-IC | Particle into liquid sampler-ion chromatography |
| PIP | Plant-incorporated protectant |
| PIPs | Plant-incorporated protectant |
| PIXE | Particle Induced X-ray Emission |
| PKI | Public key infrastructure |
| PL | Plastic limit |
| Plating and Polishing Material Metal HAP Content | Plating and polishing material metallic hazardous air pollutant content |
| Plating and Polishing Metal HAP | Plating and polishing metal hazardous air pollutant |
| PLM | Polarized light microscopy |
| PL/SQL | Procedural Language/ Source Query Language |
| PM | Particulate matter; Preventive maintenance; Program manager |
| PM 10 Emission | Particulate matter 10 emission |
| PM 2.5 | Particulate Matter 2.5 |
| PMC | PubMed Central |
| PMCID | PubMed Central ID |
| PMMA | Polymethyl methacrylate |
| PMN | Premanufacture notice |
| PMPU | Pharmaceutical manufacturing process unit |
| PMPU (Devices) | Polyether polyol manufacturing process unit |
| PMR | Proportionate mortality ratio |
| PMS | Pantone Matching System |
| PMx | Particulate matter by size |
| PNA | Polynuclear aromatic hydrocarbon |
| PO | Project officer |
| POC | Point of compliance; Point of contact |
| POC Stack | Products of combustion stack |
| PoD | Point of departure; Point of determination |
| POE | Point of exposure |
| POE Water Treatment | Point-of-entry water treatment |
| POG | Point of generation of a Hazardous Waste |
| POHCs | Principal organic hazardous constituents |
| POLL | Pollutant |
| POM | Particulate organic matter; Polycyclic organic matter |
| POTW | Publicly owned treatment works |
| POU Water Treatment | Point-of-use water treatment |
| PP | Polypropylene |
| PPA | Power purchase agreement; Prospective purchaser agreement |
| PPA Assessment | Prospective purchaser agreement assessment |
| ppb | Parts per billion |
| PPCP | Pharmaceutical and personal care product; Pharmaceuticals and personal care products |
| PPE | Personal protective equipment; Probable point of entry |
| PPG | Performance partnership grant |
| ppm | Parts per million |
| ppmv | Parts per million by volume |
| PPP | Power plant plume |
| ppt | Parts per trillion |
| PQL | Practical quantification limit; Practical quantitation level; Practical quantitation limit |
| PR | Peer review; Percentage reduction |
| PRA | Paperwork Reduction Act; Probabilistic risk analysis |
| PRB System | Permeable reactive barrier system |
| Preg Tank | Pregnant solution tank |
| Preliminary Injunction | Enforcement |
| Previous-MIL-on DTC | Previous-MIL-on diagnostic trouble code |
| PRG | Preliminary remediation goal |
| Prime Farmland | Farm area |
| PRINTOUT | COMPUTER PRINTOUT |
| Product AB | Product accreditation body |
| Production-Indexed HAP Consumption Factor | Production-indexed hazardous air pollutant consumption factor |
| Production-Indexed VOC Consumption Factor | Production-indexed volatile organic compound consumption factor |
| PRP | Potentially responsible party |
| PRPs | Potentially responsible party |
| PRTYPOLS | Priority pollutant |
| PS | Point source; Polystyrene; PostScript |
| PSA | Public service announcement |
| PSC | Polar stratospheric cloud; Potential sources of contamination |
| PSD | Prevention of significant deterioration |
| PSD Station | Prevention of serious deterioration station |
| PSES | Pretreatment standard for existing source; Pretreatment standards for existing sources |
| PSI | Pollutant standard index; Pound per square inch; Pounds per square inch |
| PSIG | Pounds per square inch gage pressure; Pounds per square inch (gauge) |
| PSL | Parallel strand lumber |
| PSNS | Pretreatment standard for new source; Pretreatment standards for new sources |
| P-TBB | p-tert-Butylbenzaldehyde |
| P-TBBA | p-tert-Butylbenzoic Acid |
| P-TBT | p-tert-Butyltoluene |
| PTE | Permanent total enclosure; Potential to emit |
| PTFE | Polytetrafluoroethylene |
| PTO | Power take-off; Power takeoff |
| PTR-MS | Proton-transfer-reaction mass spectrometry |
| PUC | Public utility commission |
| PUFA | Polyunsaturated fatty acids |
| PV | Photovoltaic |
| PVA | Polyvinyl alcohol |
| PVC | Polyvinyl chloride |
| PVC (Energy) | Photovoltaic cell |
| PVC Plant | Polyvinyl chloride plant |
| PVC Resin Grade | Polyvinyl chloride resin grade |
| PVC-Combined Process Vent | Polyvinyl chloride-combined process vent |
| PVC-Only Process Vent | Polyvinyl chloride-only process vent |
| PVCPU | Polyvinyl chloride and copolymers production process unit |
| PVDC | Polyvinylidene chloride |
| PWC | Personal watercraft engine |
| PWR Limit | Product-weighted reactivity limit |
| PWS | Performance work statement; Public water supply; Public water system |
| PWSID | Public water system ID |
| PXR | Pregnane-X-Receptor |