Estimates of atmospheric hydroxyl radical concentrations from the observed decay of many reactive hydrocarbons in well‐defined urban plumes

Abstract

An analytical system has been developed which allows the confident identification and measurement of 35 hydrocarbons of different reactivities in air samples collected in many locations. This paper describes the application of the technique to follow the differential decay of hydrocarbons in urban plumes spreading from London during the summer. The data have been used to determine atmospheric hydroxyl radical concentrations, averaged over several hours, on the assumption that the decay of the hydrocarbons is entirely due to reaction with these radicals. Hydroxyl radical concentrations were derived from the measured decay of several alkenes which agreed with theoretical estimates. There are strong indications, however, that substituted aromatic molecules decay much faster than could be accounted for solely by reaction with hydroxyl radicals; this may indicate the presence of a further chemical removal mechanism. Indirect estimates of globally averaged OH concentrations havealso been made using the measured distribution of methyl chloroform in the atmosphere [Singh et al., 1979] and the seasonal variation of •4CO [Volz et al., 1981]. Indirect estimates of OH concentrations in chemically well defined situations, such as urban plumes, can be extremely useful in validating models of regional ozone production and in understanding atmospheric photochemical theory. The plume study reported here used a high quality sampling and analytical system to collect time-resolved data over several hours on a large number of hydrocarbons, covering a wide range of atmospheric reactivity with OH radicals. OH concentrations were then derived from the decay of both aliphatic and aromatic hydrocarbons in combination with the comprehensive kinetic data base on hydrocarbon reactions with hydroxyl radicals recently published by Atkinson [1990]. 2. EXPERIMENTAL PROCEDURE 2.1. Collection of Air Samples A twin turboprop Jetstream aircraft owned and operated by the Cranfield Institute of Technology was employed for this study. Flown unpressurized, the Jetstream has an operational altitude ceiling of about 3300 m and a maximum endurance of about 4 hours at 120 knots (222 km/hr). The procedure for the collection of air samples has been described extensively in a previous publication [Lightman et al., 1990] and is therefore only briefly presented here. Discrete air samples were collected through stainless steel tubing from an intake manifold located on the aircraft roof, forward of the engines. Two metal bellows MB 158 pumps in series were employed to fill 1.6-L electropolished stainless steel sample bottles. Each bottle was fitted with a dip tube to facilitate flushing for 4 min before pressurizing to 4 atmospheres (60 psig) over a period of up to 1 min. The effect of this high pressure is to 2851 carbons in the atmosphere, Environ. Sci. Technol., 15, 113-119, 1981.

Summertime Measurements of Benzene and Toluene in Athens Using a Differential Optical Absorption Spectroscopy System

“…Thus, the explanation of the observed high values of benzene in the area during nighttime seems to be complicated. Toluene (see Figure 6) hourly values showed that the maximum values were recorded in the morning hours (7)(8) and the minimum values during afternoon hours (17-18 LT), a behavior similar to that of benzene and NO 2 , certifying that the three pollutants have the same origin. It is obvious that toluene exhibits a larger and sharper diurnal variation than that of benzene.…”

“…The specific ratios of BTX could be changed because of photochemical reactions caused by different lifetimes of the aromatics. Aromatics have been measured in some European cities in recent years, specifically in Milan, 6,7 London, 8 and Munich, 9 while Moschonas and Glavas 10 and Rappenglueck et al 11 measured aromatics in Athens using mainly the gas chromatograph (GC) (in situ or flask sampling) technique. The differential optical absorption spectrometer (DOAS) technique was recently used in Goteborg, 12 Rome, 13 and Thessaloniki.…”

Analysis of motor vehicle sources and their contribution to ambient hydrocarbon distributions at urban sites in Toronto during the Southern Ontario oxidants study

“…This would indicate that the source mixtures are similar in urban centres in the two countries. The York distribution is less similar to the distributions seen in Sydney, Australia or London, England (Blake et al, 1993). The latter two profiles appear enriched in acetylene and olefins, species known to be reactive on vehicle catalytic convertors.…”

OH clock determination by proton transfer reaction mass spectrometry at an environmental chamber

“…This concept of using reactive tracers to determine the OH concentration has been discussed (and improved) in several publications in the past, like e.g. : Singh et al (1981); Roberts et al (1984); McKeen et al (1990);Satsumabayashi et al (1992); Blake et al (1993);McKenna et al (1995); Kramp and Volz-Thomas (1997). Other studies use the ratio of NO 2 to NO y to determine the photochemical age (Kleinman et al, 2008;Slowik et al, 2011).…”