Seasonal variation of hydrocarbons in the free troposphere at mid-latitudes

Abstract

The free tropospheric concentrations of several light hydrocarbons and ozone have been measured throughout most of the year in air flows approaching the UK from unpolluted areas of the Northern Hemisphere. The measurements were made using an aircraft at altitudes between 1500 and 3000 m and concurrent measurements of halocarbons confirmed that the air had not passed recently over potential sources of hydrocarbons. Most of the hydrocarbons show a clear seasonal pattern with a summer minimum and winter maximum, but propene and ethene, which are very short‐lived in the atmosphere and have oceanic sources, show no seasonal pattern. The halocarbon concentrations also exhibit no seasonal pattern but ozone shows a spring maximum. The results for ethane and propane, which have a common anthropogenic source, are consistent with a summer to winter average OH radical concentration ratio of about 4 to 7 and a travel time for source area to sampling point of about 20 days. It is suggested that the presence of large concentrations of non‐methane hydrocarbons on an extensive scale will influence the seasonal pattern of ozone observed in large parts of the northern hemisphere.

TROPOZ II: Global distributions and budgets of methane and light hydrocarbons

“…Literature data also allow an estimate of the global tropospheric burden of CH4 independently from the TROPOZ experiment. For this purpose, based on a tropospheric air content of 8.69 x 1043 molecules (Khalil and Rasmussen, 1985), a mean methane mixing ratio of 1.690 ppmv for January 1989 (Khalil and Rasmussen, 1990), and an average annual increase rate of 0.6% (trend for the years -1990according to Steele et al (1991), the global tropospheric burden of CH4 in January 1991 is estimated at 4000 Tg-CH4.…”

A global three‐dimensional chemical transport model: 2. Nitrogen oxides and nonmethane hydrocarbon results

“…[Lightman et al, 1990] 1 ................................................ Besides the reference and the aircraft emission runs described already, three additional runs are described below. …”

C2–C5 Hydrocarbon measurements in the Netherlands 1981–1991

“…The ratio is close to unity in the marine sector (210°-330°) and up to 1.5-1.8 in the remaining sectors. Many authors have pointed out that surface waters might be a source of propene during the summer (Lightman et al, 1990;Rudolph and Johnen, 1990;Bonsang and Lambert (1985)), and the existence of nearby surface waters is often used to explain the winter to summer ratio of propene. However, Fig.…”

“…Ethane concentrations advected over the Atlantic Ocean at 40°-60°N range from 1 to 3 ppb (Rudolph and Ehhalt, 1981;Rudolph and Khedim, 1985;Tille et al, 1985;Lightman et al, 1990;Penkett et al, 1993). Concentrations of the other hydrocarbons measured simultaneously over the Atlantic Ocean are generally far below the 1 ppb level.…”

“…The concentrations measured at Moerdijk at wind speeds higher than 10 m s" 1 (Tab. 3) were compared with the concentrations measured in air parcels arriving at the United Kingdom from the Atlantic Ocean (Lightman et al, 1990;Penkett et al, 1993).…”