Visibility at Oxford, 1926–1985

Abstract

T HIS paper examines the changes which have occurred in the frequency of occasions of 'very good' or 'excellent' visibility (19km or better) at Oxford since 1925. An earlier paper (Gomez and Smith 1984) examined the decline in the frequency of fog at Oxford associated with the implementation of the Clean Air Act of 1956. The present study was undertaken in an effort to determine whether some of the influences discussed in the earlier paper might have affected the number of occasions when visibility is in the higher ranges, and also whether any of the changes have affected one season more than another.The results indicate that long range visibility has deteriorated since about 1952 but that this change is largely a feature of the summer months. They also show that there was a deterioration in long range visibility in the years before and during the Second World War and a very marked improvement immediately after the war; these changes affected all seasons. While a deterioration in summer visibility in southeast England during the last twenty years or so has been noted by others the earlier changes affecting all seasons do not appear to have been discussed previously.

Visibility impairing aerosols in the urban atmosphere of Delhi

“…The average SVR of Delhi (average of the three sites) works out to be 9.4 km, which indicates poor quality of visibility in the atmosphere of Delhi as per the definition of very good visibility as >19 km for an urban atmosphere (Gomez and Smith 1987). Conclusively thus, visibility impairment in Delhi is primarily because of the carbonaceous species.…”

“…Leavey and Sweeney (1990) reported that in a nonpolluted atmosphere, visibility would be of the order of 250 km. For an urban atmosphere, Gomez and Smith (1987) defined very good visibility as >19 km. In view of this, the visual air quality of Delhi is poor.…”

The Relationship of PM Variation to Visibility and Mixing Layer Height under Haze/Fog Condition in Multi-Cities of Northeast China

“…The days and distribution of visibility >19km and <10km in multi-cities of central Liaoning was shown in Figure 10 as classified according to Gomez and Smith [69] which has an inverse correlation in contrast to the mixing layer height.…”

Source apportionment of visibility‐degrading aerosols in the lower fraser valley, B.C.

“…These visual range estimates are actually a measure of the distance at which an observer can recognize an object with the naked eye. Some of the problems of using these data to assess visual air quality may be summarized thus (a) The measurement depends on the judgement and eyesight of the observer and the available checkpoints (Gomez and Smith, 1987). (b) The measure exhibits a diurnal signal due to changing checkpoints at night.…”

“…These average values of relative humidity suggest that particles at RPP may be hydrated, and that sample heating by the nephelometer might affect b sp measurements, particularly during winter. Work by Dzubay et al (1982) in Houston indicated that b sp measurements taken using a heated (+12.5°C above ambient) and unheated (+3.5°C above ambient) nephelometer differed by about ±15% at relative humidity ~50% and by about ±35% at relative humidity ~82%.…”