| LA | Load Allocation |
| LAA | Libby Amphibole Asbestos |
| Laboratory AB | Laboratory Accreditation Body |
| LADD | Lifetime Average Daily Dose; Lowest Acceptable Daily Dose |
| LAER | Lowest Achievable Emissions Rate |
| LAN | Local Area Network |
| Large CAFO | Large Concentrated Animal Feeding Operation |
| Large HMIWI | Large Hospital/Medical/Infectious Waste Incinerator |
| LC | Letter Contract; Liquid Chromatography; Loading Capacity |
| LC 50 | Lethal Concentration 50 |
| LC50 | Lethal Concentration 50; Median Lethal Concentration |
| LC₅₀ | Lethal Concentration₅₀ |
| LCA | Life Cycle Assessment |
| LCC | Life Cycle Costing |
| LCFS | Low Carbon Fuel Standard |
| LCI | Life Cycle Inventory |
| LCL Approach | Lower Confidence Limit Approach |
| LCLO | Lethal Concentration Low |
| LCMR | Lowest Concentration Minimum Reporting Level |
| LC-MS | Liquid Chromatography-Mass Spectrometry |
| LCR | Linear Calibration Range |
| LCS | Laboratory Control Sample |
| LCSA | Life Cycle Sustainability Analysis |
| LCT | Life Cycle Thinking |
| LD | Land Disposal; lethal dose |
| LD 50 | Lethal Dose 50 |
| LD1 | Laboratory Duplicate(s) |
| LD50 | Lethal Dose 50; Median Lethal Dose |
| LD₅₀ | Lethal Dose₅₀ |
| LDAP | Light Directory Access Protocol |
| LDC | STORET Legacy Data Center |
| LDC Custody Transfer Station | Local Distribution Company Custody Transfer Station |
| LDCRS | Leachate Detection Collection and Removal System |
| LDH | Lactate Dehydrogenase |
| Ldlo | Lethal Dose Low |
| LDM | Library Dependent Method |
| Ldn | Day-Night Sound Level |
| LDPE | Low Density Polyethylene |
| LDR | Land Disposal Restrictions; Linear Dynamic Range |
| LDS | Leak-Detection System |
| LDSFE | Fuel Economy |
| LDT | Light-duty Truck |
| LDT1 | Light-Duty Truck 1 |
| LDT2 | Light-Duty Truck 2 |
| LDT3 | Light-Duty Truck 3 |
| LDT4 | Light-Duty Truck 4 |
| LDV | Light-duty Vehicle |
| LEA | Local Education Agency |
| Lead-Acid Battery Component Manufacturing Plant | Lead-Acid Battery Manufacturing Plant |
| LED | Light-Emitting Diode |
| LED10 | Lower Limit on Effective Dose ₁₀ |
| LED₁₀ | Lower Limit on Effective Dose ₁₀ |
| LEDs | Light emitting diodes |
| LEED | Leadership in Energy & Environmental Performance; Leadership in Energy and Environmental Design |
| LEED Certification | Leadership in Energy and Environmental Design Certification |
| Legacy CCR Surface Impoundment | Legacy Coal Combustion Residuals Surface Impoundment |
| lel | lower explosive limit; lowest-observed effect level |
| LEPC | Local Emergency Planning Committee |
| Leq | Equivalent Sound Level |
| LEV | Low Emission Vehicle |
| LEVD | Low emission vapor degreasers |
| LFB | Laboratory Fortified Blank (radiochemistry) |
| LFG | Landfill Gas Emission |
| LFG Collection System | Landfill Gas Collection System |
| LFSM | Laboratory Fortified Sample Matrix (radiochemistry) |
| LFSMD | Laboratory Fortified Sample Matrix Duplicate (radiochemistry) |
| LH | Luteinizing Hormone |
| LHS | Latin Hypercube Sampling |
| LI | Langelier Index; liquidity index |
| LIBS | Laser Induced Breakdown Spectroscopy |
| LID | Low Impact Development |
| lidar | Light Detection And Ranging |
| LIM | Library Independent Method |
| Liquid Oil-Fired EGU Capacity Factor | Liquid Oil-Fired Electric Generating Unit Capacity Factor |
| LIS | Earth Observation Data |
| LL | liquid limit |
| LLD | Lower limit of detection |
| LLDPE | Linear Low Density Polyethylene |
| LLDT | Light Light-Duty Truck |
| LLJ | Low-Level Jet |
| LLOQ | Lower Limit of Quantitation |
| LLRW | Low-Level Radioactive Waste |
| LM | Light Microscopy |
| LM Diesel Fuel | Locomotive; Marine Diesel Fuel |
| Lmax | Maximum Sound Level |
| LNAPL | Light Non-Aqueous Phase Liquid; Light Nonaqueous Phase Liquid |
| LNAPLs | Light-non-aqueous phase liquids |
| LNG | Liquefied natural gas |
| LNG Boil-Off Gas | Liquefied Natural Gas Boil-Off Gas |
| LNT | Linear No Threshold Model |
| LOAEC | Lowest Observable Adverse Effect Concentration |
| LOAEL | Lowest Observable Adverse Effect Level; Lowest Observed Adverse Effect Level |
| LOC | Lab on a Chip; Letter of Credit; Level of Concern |
| LOD | Limit of Detection |
| Log | Logarithm |
| Logo | Logotype |
| LOI | Loss-on-Ignition |
| LOQ | Level of Quantitation; Limit of Quantification; Limit of Quantitation |
| Low NOx Burner | Low Nitrogen Oxides Burner |
| Low NOX Burner Technology | Low Nitrogen Oxides Burner Technology |
| low-e coating | Low-emissivity coating |
| Low-E Windows | Low Emissivity Windows |
| Low-Pressure Sodium Lamp | Lamp |
| LPC | Limiting Permissible Concentration |
| LPG | Liquefied petroleum gas |
| LPTV | Low Power Television |
| LQ | Quantification Limit |
| LQG | Large Quantity Generator |
| LQGs | Large Quantity Generators |
| LRB | Laboratory Reagent Blank (radiochemistry) |
| LRBP | Large River Bioassessment Protocol |
| LSA | Labor Surplus Area |
| LSAF | Labor Surplus Area Firm |
| LSDF | Low-Sulfur Diesel Fuel |
| LSL | Laminated Strand Lumber |
| LTM | Limiting Tracer Method |
| LTU | Land Treatment Unit |
| LUST | Leaking Underground Storage Tank |
| LVHC Collection System | Low Volume High Concentration Collection System |
| LVL | Laminated Veneer Lumber |
| LVW | Loaded Vehicle Weight |
| LWK | Live Weight Killed |
| LWR | Light water reactor |