Yi-Chun LinPh.D.Taiwan
Laser Materials ProcessingPublished
Dec 24, 2025
NOₓ
Chemical Properties
Chemical Identity
CAS Number
Various
Formula
NOx
Exposure Limits Comparison
OSHA PEL
25 ppm
ACGIH TLV
3 ppm
Health Effects
Respiratory Irritation
Yes
Pulmonary Edema
Yes
Bronchitis
Yes
Delayed Effects
Yes
NOₓ safety information
Comprehensive safety and handling requirements
Detection Monitoring
- Electrochemical
- Chemiluminescence
- NDIR
- Metal oxide
- Dräger NO2 0.5/a
- Gastec 9L
- Kitagawa 175
| Sensor Types | ||||||||||
| Detection Range | 0-50 ppm typical | |||||||||
| Alarm Setpoints |
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| Colorimetric Tubes | ||||||||||
| Analytical Methods |
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| Odor Threshold | NO2: 0.1-1 ppm (provides warning but overlaps toxic range). NO: odorless (NO WARNING). |
Environmental Impact
| Aquatic Toxicity | Toxic to aquatic life. LC50 (fish, 96h): varies by species and form. Forms acidic solutions. | ||||
| Biodegradability | Reacts in atmosphere. Converts to nitric acid. Not biodegradable. | ||||
| Bioaccumulation | Does not bioaccumulate. | ||||
| Soil Mobility | High mobility as gas. Deposits as nitrates. Contributes to soil acidification. | ||||
| Atmospheric Fate | Photochemical reactions produce ozone. Forms nitric acid with water vapor. Contributes to acid rain. Residence time: hours to days. | ||||
| Ozone Depletion | true | ||||
| Global Warming Potential | N2O: 298 (CO2=1) | ||||
| Reportable Releases |
|
Ppe Requirements
| Respiratory | SCBA or positive-pressure supplied-air respirator for >1 ppm NO2 or unknown concentrations. Air-purifying with acid gas cartridge acceptable for ≤1 ppm NO2 only. |
| Eye Protection | Chemical safety goggles, face shield for high concentrations |
| Skin Protection | Nitrile or butyl rubber gloves for liquid contact. Chemical-resistant clothing if high concentrations. |
Reactivity
- Reducing agents
- Flammable materials
- Organic materials
- Ammonia
- Carbon disulfide
- Hydrogen sulfide
- Petroleum
- Alcohols
- Nitrogen
- Oxygen
- Toxic nitrogen oxides
- Heat
- Pressure
- Incompatible materials
- Moisture (forms corrosive acids)
| Stability | NO2/N2O4 equilibrium temperature-dependent. May decompose under heat/pressure. |
| Polymerization | Will not polymerize |
| Incompatible Materials | |
| Hazardous Decomposition | |
| Conditions To Avoid | |
| Reactivity Hazard | Strong oxidizer. Reacts violently with reducing agents and combustibles. Forms nitric acid with water. May explode under heat/pressure. |
Regulatory Classification
- Acute toxicity (inhalation)
- Oxidizing gas
- Corrosive
| Un Number | UN1067 (nitrogen dioxide/dinitrogen tetroxide), UN2201 (nitrous oxide) | ||||||||
| Dot Hazard Class | 2.3 (Toxic gas), 5.1 (Oxidizer) | ||||||||
| Dot Label | Poison Gas, Oxidizer | ||||||||
| Nfpa Codes |
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| Epa Hazard Categories | |||||||||
| Sara Title Iii | true | ||||||||
| Cercla Rq | 10 pounds (4.54 kg) for NO2 | ||||||||
| Rcra Code | P078 (nitrogen dioxide) |
Storage Requirements
- Flammable materials
- Combustible materials
- Reducing agents
- Ammonia
- Carbon disulfide
- Hydrogen sulfide
- Petroleum products
| Temperature Range | Store cylinders <52°C. Keep away from heat. |
| Ventilation | Outdoor storage strongly preferred. Indoor: mechanical ventilation with emergency backup. NOx gas detection mandatory. |
| Incompatibilities | |
| Container Material | Steel cylinders for compressed gas. Stainless steel or glass for liquid. |
| Segregation | Separate from flammables and combustibles by 20 feet or firewall. Oxidizer storage area. |
| Quantity Limits | Per fire code: limit cylinders in buildings. Many facilities store outdoors only. |
| Special Requirements | Cylinder restraints mandatory. Leak detection system required. Post "OXIDIZER" and "POISON GAS" signs. Emergency procedures posted. Monitor cylinder integrity regularly. |
Produced From Contaminants
Exposure Limits
Regulatory exposure thresholds and safe concentration levels
- Osha Pel Ppm
- 25
- Osha Pel Mg M3
- 9
- Niosh Rel Mg M3
- 1.8
- Acgih Tlv Ppm
- 3
- Acgih Tlv Mg M3
- 5.6
- Workplace Exposure
- Osha Peltwa_8hr: nullstel_15min: nullceiling: 5 ppm (NO2), 25 ppm (NO)Niosh Reltwa_8hr: nullstel_15min: 1 ppm (NO2) - 15 min ceilingceiling: nullidlh: 20 ppm (NO2), 100 ppm (NO)Acgih Tlvtwa_8hr: 0.2 ppm (NO2), 25 ppm (NO)stel_15min: 1 ppm (NO2)ceiling: nullBiological Exposure Indices0: [object Object]1: [object Object]
Physical Properties
Physical characteristics and state information
- Boiling Point
- NO: -151.7°C, NO2: 21.2°C, N2O4: 21.2°C
- Melting Point
- NO: -163.6°C, NO2: -11.2°C
- Vapor Pressure
- NO: >760 mmHg @ 20°C (gas), NO2: 760 mmHg @ 21°C
- Vapor Density
- NO: 1.04 (Air=1), NO2: 1.58 (Air=1)
- Specific Gravity
- NO2: 1.45 (liquid @ 21°C)
- Flash Point
- Not applicable (non-flammable)
- Autoignition Temp
- Not applicable
- Explosive Limits
- Not applicable (supports combustion)
- Appearance
- NO: colorless gas, NO2: reddish-brown gas, N2O4: colorless liquid/gas
- Odor
- NO2: pungent, irritating odor @ 0.1-1 ppm. NO: odorless
Reactivity
Chemical reactivity and compatibility with other substances
- Stability
- NO2/N2O4 equilibrium temperature-dependent. May decompose under heat/pressure.
- Polymerization
- Will not polymerize
- Incompatible Materials
- Reducing agents
- Flammable materials
- Organic materials
- Ammonia
- Carbon disulfide
- Hydrogen sulfide
- Petroleum
- Alcohols
- Hazardous Decomposition
- Nitrogen
- Oxygen
- Toxic nitrogen oxides
- Conditions To Avoid
- Heat
- Pressure
- Incompatible materials
- Moisture (forms corrosive acids)
- Reactivity Hazard
- Strong oxidizer. Reacts violently with reducing agents and combustibles. Forms nitric acid with water. May explode under heat/pressure.
Synonyms & Identifiers
Alternative names and chemical identifiers (CAS numbers)
- Synonyms
- NOx
- Nitrogen dioxide (NO2)
- Nitric oxide (NO)
- Dinitrogen tetroxide (N2O4)
- Nitrogen peroxide
- Common Trade Names
- Other Identifiers
- Rtecs NumberQW9800000 (NO2)Ec Number233-272-6 (NO2)Pubchem Cid3032552 (NOx)
