The Effect of Atmospheric Contaminants on Light Fastness*

The reaction of dyes with atmospheric contaminants, including ozone and oxides of nitrogen, is shown to be an important factor in light‐fastness testing. Ozone, present to the extent of 0·05 to 0·2 p.p.m., is responsible for fading in exposures away from sunlight. Oxides of nitrogen also contribute to anomalous fading in industrial areas when present in concentrations up to 0·3 p.p.m. Fading has been observed on cotton dyed with certain vat, direct, sulphur, and reactive dyes, and on nylon and acetate dyed with typical dyes. Fading is greater in areas of high humidity, including sunlight exposure stations. Ozone fading is discussed in terms of occurrence, vulnerable dyes, chemical reaction, and effect of humidity. The experimental results are used to explain certain variations in light‐fastness results obtained by the AATCC in exposures at a constant number of Lacg'eys, equivalent temperatures and humidity, but in different localities. Data on various dyes and fibres are presented for three‐month exposures protected from sunlight in Los Angeles, California (an area of high NO2, very low SO2, and high ozone contents), Chicago, Illinois (moderate NO2, high SO2, and low ozone), Phoenix, Arizona (a sunlight testing station of moderate ozone, no NO2 or SO2, but low humidity) and Sarasota, Florida (a sunlight testing station of moderate ozone, no NO2 or SO2, but high humidity). Laboratory test methods for fading clue to oxides of nitrogen and ozone are correlated with the actual service‐exposure results. Exposure to irradiated car‐exhaust fumes in a laboratory chamber representing a combination of NO2 and ozone duplicates the Los Angeles exposure results. It is concluded that consideration should be given to the combined effects of atmospheric contaminants and sunlight on dyed fibres.