hydrocarbons in the atmosphere

Pageoph, Vol. 116 (1978), Birkh~user Verlag, Basel

Hydrocarbons in the Atmosphere

By ELMER ROBINSON 1)

A b s t r a c t - Trace concentrations of highly reactive hydrocarbons of biogenic origin have been proposed for some time as being important in aerosol formation processes in the atmosphere. More recently, assess- ments of potential photochemical reactions in the troposphere have proposed a role in the atmospheric ozone cycle for hydrocarbons, even for compounds such as methane that had previously been considered nonreactive. An assessment of the atmospheric hydrocarbon reaction system has been limited by a lack of observational information on the nature of conditions in the remote or non-urban atmosphere. Recent data on terpene concentrations and other biogenic hydrocarbon compounds are presented. Data on ethane and acetylene from aircraft samples taken over the north and south Pacific Ocean show concentrations in the 0.5 to 1 gg/m 3 range for ethane and in the 0.05 to 0.3 gg/m 3 range for acetylene. A concentration gradient is present for these compounds between the northern and southern hemisphere. A rudimentary global concentration pattern for these C 2 compounds has been developed on the basis of recent data.

Key words." Atmospheric Hydrocarbons; Air Chemistry; Hydrocarbon concentrations.

I n t r o d u c t i o n

The impor tance o f t race amoun t s o f n o n m e t h a n e a tmosphe r i c organic c o m p o u n d s

was po in ted ou t by W e n t in 1955 when he l inked pho tochemica l ly react ive p lan t

emiss ions to the fo rma t ion o f ae roso l par t ic les and na tu ra l 'b lue haze ' (WENT, 1955).

W e n t a t t r ibu ted these na tu ra l hazes to pho tochemic a l processes, c o m m o n l y classed as

' s m o g ' react ions, involving terpenes and o the r essential oils and p r o p o s e d tha t the

sources o f these organic gases were the na tu ra l emissions f rom vegeta t ion. The fact

tha t W e n t d id no t cons ider this a comple te ly new idea in the ident i f icat ion o f a source

o f na tu ra l haze aerosols is i l lus t ra ted by his reference to Tynda l l ' s 1869 exper iment in

which the p roduc t ion of a 'b lu ish haze ' t o o k p lace in a tube filled with o rgan ic vapors .

The magni tude o f this na tu ra l o rgan ic source was es t imated by W e n t in 1955 as

being o f the order o f 108 tons annual ly . W e n t subsequent ly refined this es t imate to a

value o f 175 x 106 tons annu~flly (WENT, 1960). As will be evident f rom the sub-

sequent discussion, this is still a r easonab le es t imate o f the magn i tude o f the na tura l

o rgan ic emiss ion; however , cons iderab le research is present ly being unde r t a ke n to

es tabl ish this rate more exactly.

The reasons for an expanded interest in na tu r a l o rganic emissions is tha t po ten t ia l

1) Washington State University, Pullman, Washington, USA.

Vol. 116, 1978) Hydrocarbons in the Atmosphere 373

atmospheric chemistry roles for these materials have expanded in recent years. Went, as mentioned above, linked the biogenic emissions to natural haze particles through photochemical reactions. These reactions involve t~ae production of ozone and with the increased attention being given to rural ozone concentrations in the mid-1970's the natural sources of reactive organics has been considered seriously as a significant cause of rural ozone. Even more recently the OH radical has assumed a very promi- nent role in atmospheric photochemistry and interactions between OH and organic biogenic emissions could be an important reaction process in the establishment of a stable atmospheric condition (e.g., WOLFSY, 1976).

The following discussion will consider, briefly, the probable magnitudes of biogenic emissions and their relationship to current anthropogenic emissions. Then some of the types of compounds found in the nonurban environment will be de- scribed on the basis of some recent research investigations, and finally some global distributions of several low molecular weight hydrocarbons will be presented.

Hydrocarbon sources

Natural sources

The sources of atmospheric hydrocarbons are known to be both biogenic and anthropogenic. The heavier hydrocarbons, especially in the terpene class, are generally considered to be the major contributions of biological sources. A wide range of compounds may be expected from the biosphere, however. For example, CAVANAGH (1969) reported the finding of a relatively high concentration of n-butanol at Point Barrow, Alaska, which was apparently given off by the decaying tundra.

Biological emissions from forests and other vegetation have been found by RmMuSSEN (1972) to consist of a variety of terpene-type compounds including ~- pinene, camphene, fl-pinene, and limonene as well as the hemiterpene isoprene. Rates of emission of gaseous terpenoid compounds emitted from undamaged foliage varies with species, maturity, and temperature as well as with the general integrity of the surface. Emission rates for isoprene are also dependent on light, with no isoprene emissions in the dark. As examples of some of these variations, Rasmussen indicates that for a temperature change from 17~ to 30-32~ there is a 5-fold increase in ~-pinene emissions by White Pine and a 7.5-fold increase by White Fir. When light intensity was varied by approximately two-fold, from 340 to 700 ft cd, the isoprene emissions of the broad-leafed tree species Oak and Sweet Gum increased approximately 4-fold and 3.5-fold, respectively. Some recent experiments on Pacific North- west trees by Z~ME~AN at Washington State University (1976) indicate terpene foliage emission rates in the range of 0.01 to 0.1 pg per minute per dry weight gram of vegetation.

These values are presented in spite of the acknowledged variations in emission rates as a function of vegetation type, quantity, and ambient conditions, because

374 Elmer Robinson (Pageoph,

they still seem to be the best available data. Furthermore, RASMUSSEN (1972) has attempted to indicate some large-scale emission rates for these compounds. His calculated emission rate for the earth's vegetated area of 108 km 2 is 117 • 106 metric tons (mT) annually for an average canopy depth of 50 cm and 464 • 106 mT

per year for an average canopy depth of 2 m. These estimates are in the same range as the 1960 global terpene emission estimate of Went of 175 • 106 mT per year (1960) as well as with Went's original 1955 estimate of 108 tons annually. For the United States with approximately 10~ of the earth's vegetated area the emission is proportionately less, 23 • 10 6 mT per year assuming a 1-m canopy depth. In terms of approximate rates from a smaller area, this emission calculates out to about 12 mg/m2/day for a 1-m canopy and a 180-day growing season. This is a very significant emission rate, especially when the compounds that are included in it are photochemically reactive. On the basis of using biogenic hydrocarbon emissions as a sink for ozone in the lower troposphere, calculations by RIPPERTON et al. (1967) indicate that Rasmussen's postulated emission rate could be low by a factor of perhaps 2 to 10.

Anthropogenic sources

Anthropogenic emissions of hydrocarbons can be estimated from production and usage estimates and related emission factors (ROBINSON and ROBBINS, 1972). These techniques are admittedly crude when applied on a global scale, but they can be at least informative for the general distribution of hydrocarbon emissions in terms of the major source categories. Petroleum refining, product handling and storage, and fuel combustion account for more than 50 percent of the total emission. The importance of this emission rate, which probably exceeds 100 • 106 tons annually at this time with 75 percent being nonmethane (DuCE, 1977), is that while it is still less than the natural biogenic emission rates of Went and of Rasmussen on a global basis, it is comparable in many areas when the actual global distribution of sources is considered. From a summation of the latitudinal distribution in the northern hemisphere of the production of energy it is found that the zone between 30 ~ and 60~

dominated in the production of energy. More specifically, more than 95 percent of the world's energy is consumed in the northern hemisphere and more than 85 percent of the global energy is consumed between 30 ~ and 60~ If a reasonable correlation between energy consumption and anthropogenic organic emissions is assumed then one can easily calculate an average zonal land area organic emission that approaches that estimated for natural sources by Rasmussen.

If only the United States is considered, the estimated total emission rate of nonmethane hydrocarbons for 1970 was 25 x 10 6 mT per year (EPA, 1973). This compares with Rasmussen's U.S. terpene emission of 23 • 106 mT per year. Thus, at least in major developed countries of the world anthropogenic emissions of nonmethane hydrocarbons are generally equivalent to the probable large-area emissions from the biosphere.


Estimates of nonmethane hydrocarbon emissions by EPA (1973) for statewide areas based on 1970 data also indicate rates of emission that are generally comparable to Rasmussen's estimate. Some representative values are:

Texas 11 mg/m2/day Louisiana 17 mg/m2/day Missouri 10 mg/m2/day Ohio 40 mg/m2/day Illinois 19 mg/mZ/day

Emissions from New Jersey are estimated at 98 mg/m2/day and were the highest of any state. Note that these large areas equal or exceed Rasmussen's natural emission estimate of 12 mg/m2/day for the total of the United States. In much of northern Europe with a greater population density the atmospheric organic levels are probably controlled even more strongly by anthropogenic emissions.

Background hydrocarbon concentrations

The nature of the background or natural mixture of hydrocarbons is impossible to define at this time and will probably always be dependent on local influences. The previously mentioned results of CAvANAGH (1969) identifying n-butanol as an emission from arctic tundra in the Fall season is an example of the influence of local sources.

In spite of the fact that a typical site and a typical mixture of natural hydrocarbons cannot be defined recent research in this area can begin to establish guidelines for background hydrocarbon concentrations. One program of extensive hydrocarbon monitoring was carried out by C ~ I A ~ D , et al. (1977) of Washington State University in rural southwestern Missouri. This research was conducted in late August 1975 using gas chromatographic techniques capable of resolving the rural hydrocarbon mixture at the low part per billion concentrations found for individual hydrocarbons in the C2 to Clo range of compounds. The area was a mixed forest and agricultural area near the small crossroads of Elkton in southwestern Missouri. The observed weather conditions varied during the sampling program. Thus the data probably give a good picture of the hydrocarbon levels found over the more rural areas of the Mississippi Valley of the United States. From these measurements it was concluded that the non-methane hydrocarbon loading of the rural atmosphere is variable in concentration, composition, and reactivity. Although the identity and photochemical reactivity of only about half of the individual species were considered to be well determined, it appeared that there were enough reactive hydrocarbons to play an important role in determining the ozone concentrations at this rural site. Hydro- carbon concentrations were apparently determined by a combination of local natural sources and long distance transport from large urban areas.

In this Missouri study, determinations of the concentrations of individual


hydrocarbons were made in the field within an hour of air sample collection. Hydro- carbon analyses were performed using three Perkin-Elmer PE 3920 flame ionization gas chromatographs. Separate analyses were made of the C: hydrocarbons, the C2--C6 hydrocarbons, and the C4--C~o hydrocarbons. The overlap in carbon number among the replicate analyses provided a check of the determinations for individual compounds. A liquid oxygen cryogenic concentration step was used because of the low ambient concentrations. Concentration values were obtained from peak areas. Identification was made by comparing retention times of sample and standard peaks. On any given sample 30 to 60 percent of the peaks were not separately quantified. These Were classed as 'others' in the tabulation of compounds. In addition some compounds, like hexane and benzene, were not completely separated from other trace materials, and so their identification was added to an 'others' category. More than 60 samples were analyzed in this study. A more detailed description of the WSU experiment and the analytical techniques is available in RASMUSSEN et al. 1976.

The Missouri data were interpreted by selecting the most distinct chromatographic peaks and subjecting them to a statistical analysis. Figure 1 is one result. Most

RANGES OF CONCENTRATIONS OF INDIVIDUAL

HYDROCARBON SPECIES ELKTON, MO., 19"?'5

2 o

I ~ ~ ~ ~.

i o

Figure 1 Ranges of concentrations of individual hydrocarbon species observed at Elkton, Missouri, 1975. The short horizontal bar indicates the median concentration, the boxes the central 50 percent of the distributions of concentrations, and the ~tails' the maximum and minimum concentrations observed. Ref: CHATFIELD

et al. (1977).


identified compounds show median concentrations of around 1 gg/m 3 although the median for isoprene was about 4 I.tg/m 3 and for e-pinene 0.2 I.tg/m 3. There was some concern expressed about the correct identification of c~-pinene, however, because of the lack of coniferous trees in the local area. This question is important because of the significance of this terpene compound in the estimates of biogenic emissions.

A number of attempts have been made to identify the terpene compounds in the ambient atmosphere in rural or forested areas. This has been a difficult task and until recently has not been successful unless the sample was taken well within the foliage. LONNZMAN (1976), working within a North Carolina pine forest and under the canopy, has reported considerably higher concentrations than found by WSU in Missouri, namely 5 ug/m 3 for isoprene and about 20 gg/m 3 for 7-pinene. The reasons, until recently, for the general inability of investigators to identify the terpene materials in ambient air samples are believed to be the rapid reactivity of these compounds with natural background ozone as well as the difficulty in making field measurements of these compounds with reaction losses occurring in the sample handling system.

In these Missouri samples probably the most significant hydrocarbon compound, at least photochemically, was isoprene because it reacts with ozone in the dark and

20

15

MOSPHERIC ISOPRENE LEVELS I

o WOOD SAMPLE [] TRAILER SAMPLE

;I

I

I f I I I

25 26 27 28 29 50 51 I AUGUST SEPT.

DATE

Figure 2 Isoprene concentration in air samples collected in the woods and near the trailer laboratory, Elkton,

Missouri, 24 August to 1 September 1975. Ref: CHATFIELD et al. (1977).


? E

::L

6.0-

5.0-

4.0-

3.0-

2,0,

I.O.

DIURNAL CONCENTRATION

0 0

CDT

4

ISOPRENE

SUNRISE SUNSET

ib HOUR,

-3.0

-2.0

E 6, ~k

-I.0

Figure 3 Average diurnal cycles for isoprene and ethylene, Elkton, Missouri, 24 August to 1 September 1975.

Ref: CHATFIELD et al. (1977).

also reacts photochemically to produce ozone. Figure 2 shows the diurnal cycles of isoprene in Missouri for both woods and meadow or trailer locations. These samples are consistent with the isoprene emission model for deciduous trees suggested by JONES and RASMUSSEN (1975) in which the emission is dependent on both light intensity and leaf temperature.

Figure 3 shows the average diurnal cycles for isoprene and ethylene. In contrast to the late afternoon maximum for isoprene, ethylene shows its highest concentration at night. CI-IAaXI~D et al. (1977) postulated soil and plant respiration processes as a source for ethylene in the Missouri biosphere.

A detailed statistical analysis was performed on the Missouri samples (CHA~I~D et al., 1977), and of the identified compounds isoprene, ethylene, and ~-pinene were the most clearly identified natural emission compounds.

A field laboratory analysis of ambient hydrocarbons has also been carried out by CAVANAGH et al. (1969) of Stanford Research Institute. This was done at Point Barrow, Alaska for two weeks in the Fall of 1967. Table 1 shows the average concentrations of the more than 50 analyses made over a two-week period. As indicated by Table 1, the SRI Point Barrow sampling program showed part per billion concentrations of a number of organics, including low molecular weight saturated hydrocarbons, acetone, and several alcohols. Methane was observed to have a mean concentration of 1.6 ppm over this study period. The most notable finding in this sampling program, however, was the identification of n-butanol in all of the samples at concentrations


Table 1 Average Hydrocarbon Concen- trations Point barrow, Alaska September, 1967 [Ref: CAVa-

NAGH et al. (1969)]

Ethane 0.05 ppb Butane 0.07 ppb Pentane 0.02 ppb Benzene 0.10 ppb Acetane 0.08 ppb n-butanol 200.00 ppb Methane 1.60 ppm

ranging from about 50 to 500 ppb. Thus, the n-butanol concentrations dwarfed all of the other organics combined, with the exception of methane. On a total carbon basis but neglecting butanol (200 ppb) and methane (1.6 ppm), the Point Barrow samples appear to average between 6 and 10 gg C/m 3. When the butanol is added to get the total non-CH 4 carbon, the data indicate about 530 ~tg C/m 3. Condensation nuclei counts were barely detectable and averaged about 200/ml. Thus the air samples were judged to be unaffected by local contamination sources.

The Missouri and Point Barrow programs clearly show the complexity of the atmospheric hydrocarbon burden. Differences between the two results doubtless represent differences in vegetation. Improvements in analytical techniques between 1967 and 1975 are another likely contributing factor to the observed differences.

Global hydrocarbon distributions

A major interest in air chemistry models is the development of large scale or global relationships applicable to some sort of average air chemistry. Although the data given above clearly show the problems that can influence data taken at the surface, these same factors do not necessarily apply to data taken in the troposphere above the surface boundary layer through the use of aircraft sampling techniques. RAS- MUSSBN and ROBINSON (1977) have reported C 2 hydrocarbon data over the Pacific from about 75~ to 60~ in both the troposphere and the stratosphere. These results, along with other sea level shipboard samples, provide a beginning for a global hydrocarbon distribution and thus are worthy of a closer examination.

The air samples for methane and C 2 hydrocarbon analysis were obtained between 26 October and 18 November 1976 aboard the NASA Convair 990 'Galileo II' as part of a NASA-sponsored air sampling program. Concentration limits did not permit analyses to be made of heavier hydrocarbons in these air samples. The NASA 990 mission began at Moffett Field, California and included overnight or longer stops on the out-bound mission at Fairbanks, Alaska; Honolulu, Hawaii; Pago


Pago, American Samoa; Sydney, Australia; Melbourne, Australia; and Christchurch, New Zealand. The return to Moffett Field from Christchurch was via Pago Pago and Honolulu.

The sampling system used by WSU aboard the NASA 900 consisted of a ram air probe to supply an air stream that was split between an on-board, real-time halo- carbon analyzer and a whole-air pressurized sample collection system. The pressurized samples were used for these hydrocarbon analyses. In the 990 system a metal bellows pump was used, through a valving and purging system, to pressurize air samples into 6-1 stainless steel, internally electropolished canisters. The final pressure was about 15 psig. This system has been proven to be very satisfactory for halocarbons and most other trace constituents of the atmosphere. Unfortunately the system is apparently not satisfactory for ethylene because this, or a material with the same gas chromatographic characteristics, is a contaminant in Teflon, and the small amounts of Teflon that are necessary components of the metal bellows pump provide a source that can contaminate the pressurized samples. This situation resulted in apparently high and erratic C2H 4 data. The data for CH4, C 2H 6 and C 2 H 2 are apparently unaffected. Laboratory tests have confirmed this conclusion.

Analyses on the field samples were done in the WSU laboratory using flame ionization gas chromatographic techniques developed for background air chemistry studies over the past several years.

Table 2 shows the results of a simple statistical analysis of the hydrocarbon data taken north of 25~ and south of 25~ i.e., the data taken outside the tropics in both

Table 2 Ace ty lene and ethane concentrations Nov. 76 - N A S A 990

C2H 2 (~g/m 3) C2H 6 ([tg/m 3)

Trop Strat Trop Strat

25~176 0.22(9) 0.05(8) 1.09(9) 0.55(8) 25~176 0.09(17) 0.03(3) 0.49(17) 0.28(3)

(n) = number of samples

hemispheres. For the northern hemisphere, Table 2 shows that the stratospheric concentrations of acetylene and ethane are significantly lower than the tropospheric average values. In this case the identification of a stratospheric sample was based mainly on a very high concurrent ozone concentration, but also on altitude. This tropospheric-stratospheric difference is statistically significant.

In the southern hemisphere, the trace hydrocarbon levels in the troposphere, based on 17 available samples, show that the southern tropospheric concentrations of acetylene and ethane are about 50 percent lower than the northern troposphere values. This is a statistically significant difference. There were only three samples


available from the stratosphere in the southern hemisphere; this is obviously not

enough data on which to base quantitative results. However, since the scatter in these three samples is small and they represent two separate flights on different days

they are useful data. For acetylene and ethane the concentrations in the southern stratosphere are about half the concentrations found in the northern hemisphere.

These latter differences in mean concentrations are statistically significant at the 5 percent level, although the limited number of southern hemisphere samples must

still be a limitation for these set of data.

Figure 4 compares the November 1976 aircraft data f rom the Pacific with other

available WSU background studies made over the ocean. These are the March 1974

cruise of the USNS Hayes from Hawaii to Tahiti (RASMUSSEN, 1974b) indicated as 'PAC-74' and the October 1973 cruise of the 'Meteor ' f rom H a m b u r g to the Caribbean

(RAsMUSSEn, 1974a), indicated as 'ATL-7Y.

The tropospheric global latitudinal pat tern for ethane and acetylene that is

indicated by Figure 4 shows the highest concentrations in the mid-latitudes of the

northern hemisphere. Both Pacific and Atlantic data are essentially equivalent north of about 20~ To the south of 20~ only Pacific data are available, and concentra-

tions decrease through the 2 zones 20~ to 0 ~ and from 0 ~ to 20% for both the

I

C2H 2 & C 2H 6 OCEANIC CONCENTRATIONS

.25 -

D51 ,

9O

PAC-76

PAC-76

ATL-73

PAC-74 PAC-76 ql

ALT-75

PAC-76

PAC-?4 ~ '~ ' : "~" PAC-76

PAC-76 4 PAC-74

,4 PAC-76 < PAC-'76

,11 PAC -74

- I . 0

- - . 8

~ . 6

- - . 4

- - . 2

I I 1 1 I I i I 70 50 30 I0 0 I0 5(3 50 70 90

f ) tO

3

~ ON

Figure 4 Tropospheric concentrations of acetylene and ethane over the Pacific and Atlantic Oceans as a function of

latitude. See text for details on dates and geographic areas.

382

TROPOSPHERIC

Elmer Robinson (Pageoph,

ACETYLENE B CARBON MONOXIDE CONCENTRATIONS OVER THE PACIFIC ~ NOVEMBER, 1976

C2H 2 NASA-990 CO W. SELLER (1974)

O.E w

0.. ~ -

E O A - - c . :L

0 2 - -

0 .2 - -

0.1--

o

~ ~ I i I I ,o o , o 5'0 90

Figure 5 Tropospheric acetylene concentrations over the Pacific Ocean in November 1976 compared with the global

average carbon monoxide distribution estimated by SEILER (1974).

3

O - 2 0

- - .15

- - . I

- , 0 5

November 1976 aircraft data and the March 1974 ship data. South of 20~ only November 1976 aircraft data are available but the indications are that the mid- latitudes of the southern hemisphere experience higher concentrations of acetylene and ethane than do the tropical zones.

The mid-continent data from Elkton previously shown in Fig. 1, indicates hydrocarbon levels 2-3 times higher than the mid-latitude oceanic data.

Acetylene is generally considered as an urban pollutant tracer (e.g., see CHAT- F/nO etal., 1977) with a low rate of reactivity as judged by ozone formation. BUF~INI et al. (1976), for example, class both acetylene and ethane as nonreactive along with carbon monoxide and methane. The source of ethane, at least in urban areas, is frequently attributed to natural gas leakage (STEPHENS and BURLESON, 1969). Thus if both of these compounds, acetylene and ethane, are relatively nonreactive tracers of urban emissions the apparent northern hemisphere mid-latitude maximum shown by the data plotted in Fig. 4 may be an indication of a global impact of these emissions. Such a pattern is similar to that developed for carbon monoxide by SEILER (1974) and attributed by many investigators to urban CO emissions.

Figure 5 shows the individual acetylene samples from the October 1976 sampling flight plotted as a function of latitude. The dashed line represents a visual approxima- tion of a median latitudinal distribution for these data. This figure also shows


SErL ER'S (1974) latitudinal CO distribution. The differences in acetylene concentrations between the northern and southern hemispheres is quite apparent; however, whether or not the minimum at the equator is real cannot be estimated at this time. Also, whether the more or less uniform southern hemispheric concentration of about 0.1 gg/m 3 represents transport from the northern hemisphere, or southern hemis-

pheric anthropogenic emissions, or a southern hemispheric biogenic background cannot be estimated at this time. The differences between the hemispheres for both CO and acetylene appear to be similar in relative change.

Conclusions

This assessment of atmospheric nonmethane hydrocarbons leads to a number of conclusions about the present distribution of these compounds in the atmosphere and our current state of knowledge about them.

In the case of sources, the biosphere is considered to be a major contributor of hydrocarbons to the atmosphere; this would appear to be especially important in the case of reactive compounds such as isoprene and the terpenes. These compounds are considered to be important in the formation of ozone and photochemical haze and may be important in the atmospheric OH cycle. In many large areas with large populations, urban emissions may exceed the biogenic emissions. The United States' midwest is one such area.

The compounds that may be found in a nonurban atmospheric hydrocarbon mixture have been shown to consist of a wide range of materials. This mixture obviously represents advected air mass levels and the local biogenic mixture obviously represents advected air mass levels and the localbiogenic emissions, which in them- selves may change rapidly. Except over the ocean or remote desert areas it seems likely that there will be no average or typical background mixture of atmospheric hydrocarbons.

The fact that relatively large urban emissions of very low reactivity compounds such as acetylene occur has apparently produced a disturbed global concentration pattern in the northern hemisphere and also may be reflected in higher concentrations occurring in the southern hemisphere. This was observed in the Fall of 1976. The possible impact of such a distribution of hydrocarbon emissions needs to be considered carefully.

A cknowledgtements

In the preparation of this report considerable use has been made of a number of research programs carried out at Washington State University and supported by several agencies. The Coordinating Research Council was a major contributor with

384 Elmer Robinson

support for the Missouri field studies and the analysis of the Pacific samples for light hydrocarbons. Other programs were supported by the Environmental Protection Agency. The assistance of my colleagues R. A. Rasmussen and R. B. Chatfield is also sincerely appreciated.

REFERENCES

BUFALINI, J. J., WALKER, T. A. and BUFALINI, M. M. (1976), Ozone formation potential of organic compounds, Env. Sci. Technol. 10, 908 912.

CAVANAGR, L. A., SCHADT, C. F. and ROBINSON, E. (1969), Atmospheric hydrocarbon and carbon monoxide measurements at Point Barrow, Alaska, Environ. Sci. Technol. 3, 251-257.

CHATFIELD, R. B., RASMUSSEN, R. A. and HOLDREN, M. W. (1977), Hydrocarbon species in rural Missouri air, Accepted for publication, J. Geophys. Res.

DucE, R. A. (1977), Speculations on the budget of particulate and vapor phase non-methane organic carbon in the global troposphere, Pure appl. Geophys. 115, this issue.

JONES, C. A. and RASMUSSEN, R. A. (1975), Production of isoprene by leaf tissue, Plant Physiology 55, 982-987.

LONNEMAN, W. A. (1976), Ozone and hydrocarbon measurements in recent oxidant transport studies, Paper 5-5, International Conference on Photochemical Oxidant Pollution and its Control, Raleigh, NC, September, 1976.

RASMUSSEN, R. A. (1972), What do the hydrocarbons from trees contribute to air pollution?, J. Air Pollut. Control Assoc. 22, 537 543.

RASMUSSEN, R. A. (1974a), Light hydrocarbons over the Atlantic Ocean, Report to Coordinating Research Council, Washington State University, 22 January 1974.

RASMUSSEN, R. A. (1974b), Ozone and C 2 hydrocarbons over the Pacific Ocean, Report to Coordinating Research Council, Washington State University, 20 August 1974.

RASMUSSEN, R. A., CHATFIELD, R. B., HOLDREN, M. W. and ROBINSON, E. (1976), Hydrocarbon levels observed in Midwest rural open-forested area, report to the Coordinating Research Council, Contract Number CAPRAC-11, Chemical Engineering Department, Washington State University, Pullman, WA.

RASMUSSEN, R. A. and ROBINSON, E. (1977), Atmospheric hydrocarbon concentrations in global background air samples, Report 77-13-48 College of Engineering, Washington State University to Coordinating Research Council, New York, July 1977.

RIPPERTON, L. A., WHITE, O. and JEFFERIES, H. E. (1967), 'Gasphase ozone-pinene reactions', 147th National Meeting, ACS, Chicago, IL, September 1967.

ROBINSON, E. and ROBBINS, R. C., Emissions, concentrations, and fate of gaseous atmospheric pollutants, in Air Pollution Control, Part II (W. Strauss, ed.), pp. 1-93 (Wiley-Interscience, New York, 1972).

SEILER, W. (1974), The cycle of atmospheric CO, Tellus 26, 116-135. STEPHENS, E. R. and BURLESON, F. R. (1969), Distribution of light hydrocarbons in ambient air, J. Air Pollut.

Control Assoc. 19, 929436. U.S. EPA (1973), National Air Monitoring Program, Annual Report, II, EPA-450/1-73-001-b. WENT, F. W. (1955), Global aspects of air pollution as checked by damage to vegetation, Proc. Third Nat.

Air Pollution Symposium, Stanford Research Institute, Menlo Park, CA. WENT, F. W. (1960), Organic matter in the atmosphere and its possible relation to petroleum formation,

Proc. Nat. Acad. Sci. 46, 212-221. WOLFSY, S. C. (1976), Ann. Rev. Earth Plan. Sci. 4, 441 469. ZIMMERMAN, P. (1976), Private communication.

(Received 15th July 1977)

hydrocarbons in the atmosphere

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