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DESIGNATIONS
CAS No.:
Registry name: Nitrogen oxides
Chemical name: Nitrogen oxides
Synonyms, Trade names: NOx, N-oxides, Nitrous gases
Chemical name (German): Stickstoffoxide, Stickoxide, Nitrose Gase
Chemical name (French): Oxydes d'azote
Appearance: brownish yellow - reddish brown gases depending on temperature and concentration
Note: "Nitrogen oxides" is a collective name of compounds of nitrogen with oxygen (often abbreviated NOx). Mainly nitrogen monoxide (NO) and nitrogen dioxide (NO2) are relevant to environmental impacts. Other oxides such as N2O, N2O3 and N2O5 are of minor importance in this respect.
| CAS No. | 10102-43-9 | 10102-44-0 |
| Chemical name: | Nitrogen monoxide | Nitrogen dioxide |
| Synonyms, Trade names: | Nitrogen oxide, Nitrogen(II)oxide | Nitrogen peroxide, Nitrogen(IV)oxide |
| Chemical name (German): | Stickstoffmonoxid | Stickstoffdioxid |
| Chemical name (French): | Oxyde d'azote | Bioxyde d'azote |
| Appearance: | colourless and odourless gas | reddish brown gas with penetrating, acidic odour |
BASIC CHEMICAL AND PHYSICAL DATA
| Empirical formula: | NO | NO2 |
| Rel. molecular mass: | 30.01 g | 46.01 g |
| Density: | 1.34 g/l at 0°C | 1.45 g/cm3 |
| Relative gas density: | 1.04 | |
| Boiling point: | -152°C | 21°C |
| Melting point: | -164°C | -11°C |
| Vapour pressure: | 960 hPa | |
| Solvolysis/solubility: | in water: 73.4 ml/l at 0°C | |
| Conversion: | 1 ppm = 1.247 mg/m3 1 mg/m3 = 0.8702 ppm |
1 ppm = 1.91 mg/m3
1 mg/m3 = 0.52 ppm |
Note:
NO2 is in a temperature-dependent equilibrium with
its dimer N2O4. Below 0°C, all NO2
molecules have dimerised; at higher temperatures, the equilibrium
is shifted towards NO2. Above 150°C, NO2
begins to dissociate forming NO and O2. This reaction
goes to completion at about 650°C.
ORIGIN AND USE
Origin/derivation:
NOx are major air pollutants. They are produced in all
combustion processes. In 1982, total emissions in Germany were
about 3 Mio t. The major part of the emissions comes from motor
vehicle exhausts (50%), power plants (30%) and industry (15%).
Additionally, considerable amounts are produced by soil bacteria
(denitrification) [RÖMPP, 1985].
Use:
Nitrous gases (NO/NO2) are used in the production of
nitric acid (oxidation of NH3) and sulphuric acid
(lead chamber process). Additionally, NO is used in nitrosation
processes, and NO2 (N2O4) is
used as an oxidising agent and in the manufacture of explosives.
Toxicity
| Humans: | LCLo 200 ppm, inhalation (1 min), (NO2) | acc. UBA, 1986 |
| TCLo 90 ppm, inhalation (40 min), (NO2) | acc. UBA, 1986 | |
| Mammals: | ||
| Rat: | LC50 88 ppm, inhalation (4 h), (NO2) | acc. UBA, 1986 |
| LC50 8.8 ppm, inhalation (4 h), (NO2) | acc. HORN, 1989 | |
| Mouse: | LCLo 250 ppm, inhalation (30 min), (NO2) | acc. UBA, 1986 |
| Rabbit: | LC50 315 ppm, inhalation (15 min), (NO2) | acc. UBA, 1986 |
| Dog: | LCLo 123 mg/m3, inhalation, (NO2) | acc. UBA, 1986 |
| Guinea pig: | LC50 30 ppm, inhalation (1 h), (NO2) | acc. UBA, 1986 |
| Hamster: | LC50 36 ppm, inhalation (48 h), (NO2) | acc. UBA, 1986 |
| Monkey: | MCL 44 ppm (6 h), (NO2) | acc. HORN, 1989 |
| Aquatic organisms: | ||
| Mosquito fish: | TLm 72 ppm (96 h, freshwater), (NO2) | acc. UBA, 1986 |
| Cockle: | LC50 330-1,000 ppm (48 h, saltwater), (NO2) | acc. UBA, 1986 |
Characteristic effects:
Humans/mammals: Nitrogen monoxide is oxidised forming nitrogen dioxide when it comes into contact with air. Thus, poisoning by nitrous gases is mainly due to nitrogen dioxide. Nitrogen dioxide is highly toxic and irritates both the skin and the mucous membranes. Dilutions of between 0.2 and 0.5 g/m3 can be inhaled without any adverse effects over a longer period (UBA, 1986). Nitrogen dioxide penetrates the alveoli. The formation of nitrous/nitric acid in the pulmonary tissue damages the capillary walls causing oedema after a latent period of 2-24 hours. Typical symptoms of acute poisoning are burning and running eyes, cough, dyspnoea and finally death.
Plants: Different species of plants exhibit considerable divergence in terms of resistance. All nitrous gases turn the edges of leaves brown or brownish black and cause blotches. Plant cells start to shrink and protoplasms detach themselves from the cell wall. This process ultimately results in the damaged parts of the cell drying out.
ENVIRONMENTAL BEHAVIOUR
Air:
90% of nitrogen oxide emissions come from furnaces and
combustion engines. Thus, nitrogen monoxide is predominant in the
vicinity of the source, whereas some 80% is transformed into
nitrogen dioxide following long-distance transportation. Nitrogen
oxides play an important role in the formation of ozone in the
low atmospheric layer. Nitrogen dioxide is decomposed by sunlight
into nitrogen monoxide and atomic oxygen which reacts immediately
with atmospheric oxygen molecules, forming ozone. This
equilibrium reaction depends on the NO2/NO ratio and
on the intensity of the sunlight. Especially in summer and at
high traffic volumes, this ratio is increased by atmospheric
reactions of volatile hydrocarbons from automobile exhaust fumes
resulting in a strong increase of the ozone concentration.
Nitrogen oxides are washed out from the atmosphere by
precipitation as nitrous or nitric acid, respectively.
Water:
Nitrogen oxides are only slightly soluble in water but they
form nitrous or nitric acid when they come into contact with
water. In Germany, nitrogen dioxide is listed in water hazard
class 1.
Soil:
The adverse effects in soil result from its acidification
which may cause nutrient relocation and elution depending on the
soil type.
ENVIRONMENTAL STANDARDS
| Medium/ acceptor |
Sector | Country/ organ. |
Status | Value | Cat. | Remarks | Source |
| Nitrogen dioxide | |||||||
| Air: | CDN | (L) |
0.06-0.1 mg/m3 |
Annual average | acc. BUB, 1986 | ||
| CDN | (L) |
0.2 mg/m3 |
24 h | acc. BUB, 1986 | |||
| CDN | (L) |
0.4 mg/m3 |
1 h | acc. BUB, 1986 | |||
| CH | (L) |
0.03 mg/m3 |
Annual average | acc. BUB, 1986 | |||
| CH | (L) |
0.08 mg/m3 |
24 h | acc. BUB, 1986 | |||
| D | L |
0.2 mg/m3 |
MIK | 30 min | acc. UBA, 1986 | ||
| D | L |
0.1 mg/m3 |
MIK | 24 h | acc. UBA, 1986 | ||
| D | L |
0.05 mg/m3 |
MIK | 1 a | acc. UBA, 1986 | ||
| D | L |
0.1 mg/m3 |
IW1 | acc. TA-Luft, 1986 | |||
| D | L |
0.3 mg/m3 |
IW2 | acc. TA-Luft, 1986 | |||
| D | G |
0.2 mg/m3 |
1/2 h, VDI | acc. BUB, 1986 | |||
| D | G |
0.1 mg/m3 |
24 h, VDI | acc. BUB, 1986 | |||
| E | L |
0.4 mg/m3 |
1/2 h | acc. MEINL et al., 1985 | |||
| E | L |
0.1 mg/m3 |
Annual average | acc. MEINL et al., 1985 | |||
| E | L |
0.565 mg/m3 |
Smog alarm level I | acc. MEINL et al., 1985 | |||
| E | L |
0.75 mg/m3 |
Smog alarm level II | acc. MEINL et al., 1985 | |||
| E | L |
1 mg/m3 |
Smog alarm level III | acc. MEINL et al., 1985 | |||
| EC | (L) |
0.2 mg/m3 |
98% percentile, year | acc. LAU-BW, 1989 | |||
| EC | (L) |
0.05 mg/m3 |
50% percentile, year | acc. MEINL et al., 1985 | |||
| F | (L) |
0.2 mg/m3 |
24 h, 95% percentile | acc. MEINL et al., 1985 | |||
| GR | L |
0.2 mg/m3 |
1 h, smog warning | acc. MEINL et al., 1985 | |||
| GR | L |
0.5 mg/m3 |
1 h, smog alarm stage I | acc. MEINL et al., 1985 | |||
| GR | L |
0.7 mg/m3 |
1 h, smog alarm stage II | acc. MEINL et al., 1985 | |||
| I | G |
0.2 mg/m3 |
1 h | acc. MEINL et al., 1985 | |||
| J | (L) |
0.074-0.112 mg/m3 |
24 h | acc. BUB, 1986 | |||
| NL | (L) |
0.15 mg/m3 |
24 h | acc. BUB, 1986 | |||
| NL | G |
0.095 mg/m3 |
4 h | acc. BUB, 1986 | |||
| NL | (L) |
0.3 mg/m3 |
1 h | acc. BUB, 1986 | |||
| SF | (L) |
0.15 mg/m3 |
24 h | acc. OECD, 1988 | |||
| SF | (L) |
0.3 mg/m3 |
1 h | acc. OECD, 1988 | |||
| USA | (L) |
0.1 mg/m3 |
Annual average | acc. BUB, 1986 | |||
| WHO | G |
0.03 mg/m3 |
Annual average | acc. BUB, 1986 | |||
| WHO | G |
0.095 mg/m3 |
4 h | acc. BUB, 1986 | |||
| WHO | G |
0.4 mg/m3 |
1 h, human beings | acc. LAU-BW, 1989 | |||
| WHO | G |
0.15 mg/m3 |
24 h, human beings | acc. LAU-BW, 1989 | |||
| WHO | G |
0.095 mg/m3 |
4 h, vegetation | acc. LAU-BW, 1989 | |||
| WHO | G |
0.03 mg/m3 |
24 h, vegetation | acc. LAU-BW, 1989 | |||
| Emiss. | D | L |
500 mg/m3 |
mass flow > 5 g/h2) | acc. TA Luft, 1986 | ||
| Workp | D | L |
9 mg/m3 |
MAK | DFG, 1989 | ||
| Workp | SU | (L) |
2.mg/m3 |
acc. SORBE, 1989 | |||
| Workp | USA | (L) |
10 mg/m3 |
STEL | ACGIH, 1986 | ||
| Nitrogen monoxide | |||||||
| Air: | CDN | (L) |
0.2 mg/m3 |
Long-time value | acc. OECD, 1986 | ||
| CH | G |
0.2 mg/m3 |
Annual average | acc. MEINL et al., 1985 | |||
| CH | G |
0.6 mg/m3 |
30 min, 95% percentile | acc. MEINL et al., 1985 | |||
| D | L |
1 mg/m3 |
30 min | acc. UBA, 1986 | |||
| D | L |
0.5 mg/m3 |
24 h | acc. UBA, 1986 | |||
| D | L |
0.1 mg/m3 |
MIK | 1 a | acc. UBA, 1986 | ||
| D | L |
0.2 mg/m3 |
IW1 | TA-Luft | acc. UBA, 1986 | ||
| D | L |
0.6 mg/m3 |
IW2 | TA-Luft | acc. UBA, 1986 | ||
| D | (L) |
0.5 mg/m3 |
24 h, VDI-R. 2310 | acc. LAU-BW, 1989 | |||
| D | (L) |
1 mg/m3 |
30 min, VDI-R. 2310 | acc. LAU-BW, 1989 | |||
| J | (L) |
0.075-0.1 mg/m3 |
Long-time value | acc. acc. OECD, 1986 | |||
| YU | (L) |
0.085 mg/m3 |
Long-time value | acc. OECD, 1986 | |||
| YU | (L) |
0.085 mg/m3 |
Short-time value | acc. OECD, 1986 | |||
| Workp | USA | (L) |
30 mg/m3 |
TWA | ACGIH, 1986 | ||
| Workp | USA | (L) |
45 mg/m3 |
STEL | ACGIH, 1986 | ||
Comparison/reference values
| Medium/origin | Country | Value | Source |
| Air | |||
| NO3 radical, at night | 350 ppt | acc. UBA, 1988 | |
| NO3 on particles | S |
0.5-3 mg/m3 (nitrogen) | acc. UBA, 1987 |
| PAN1), afternoons | USA |
40 ppb | acc. UBA, 1988 |
| PAN1) | S |
0.1-2 mg/m3 (nitrogen) | acc. UBA, 1987 |
| HNO2, motorway intersections | USA |
8 ppb | acc. UBA, 1988 |
| HNO2 | S |
0.1-0.3 mg/m3 (nitrogen) | acc. UBA, 1987 |
| HNO3 | S |
0.5-3 mg/m3 (nitrogen) | acc. UBA, 1987 |
Note:
All values for Sweden relate to rural areas in southern
Sweden.
1) pan = peroxide, acetyl nitro
2) no and NO2, stated as NO2
Assessment/comments
As nitrogen oxides and their related products are highly toxic to humans and hazardous to the environment, their emission should be reduced as far as possible e.g. by using catalysts in automobiles.