Sulphur dioxide, oxides of nitrogen and ozone measured continuously for 2 years at a rural site

Abstract

Continuous specific measurements of sulphur dioxide, nitric oxide, nitrogen dioxide and ozone have been made for over 2y at Bottesford, a rural site in central England, 20 km away from town and industry sources and 1 km from traffic sources. Statistics of hourly, daily, monthly, seasonal and yearly values are given. On an annual basis, there was 50% more oxides of nitrogen (nitric oxide plus nitrogen dioxide) than sulphur dioxide, and more ozone than either. The nitric oxide and nitrogen dioxide were approximately equal. No other published annual values of nitric oxide, nitrogen dioxide and ozone at U.K. rural sites are known. The summer nitric oxide values were greater at this site than at three other rural sites in the British Isles for which summer nitric oxide values have been reported, but so was the sulphur dioxide, and the amounts of both these gases probably reflect the size and distance of combustion sources. Diurnal variations of the four gases during summer months at Bottesford were similar to those published for a site in southern England. The diurnal variations for winter months at Bottesford were somewhat different, especially for nitrogen dioxide. No other published winter patterns are known. Usually nitrogen dioxide and ozone concentrations were in opposition, both short and long term, but on rare occasions, for example in relatively clean winter air, the ozone concentration rose and fell directly with the nitrogen dioxide. Hourly ozone values exceeded 50 ppb (10 −9, by volume) for several hours a month in 22 months out of 24. The World Health Organisation guideline for public health exposure limits is given as 50–100 ppb h −1, not to be exceeded more than once per month.