Rainer Steinbrecher

A global model of natural volatile organic compound emissions

Numerical assessments of global air quality and potential changes in atmospheric chemical constituents require estimates of the surface fluxes of a variety of trace gas species. We have developed a global model to estimate emissions of volatile organic compounds from natural sources (NVOC). Methane is not considered here and has been reviewed in detail elsewhere. The model has a highly resolved spatial grid (0.5° × 0.5° latitude/longitude) and generates hourly average emission estimates. Chemical species are grouped into four categories: isoprene, monoterpenes, other reactive VOC (ORVOC), and other VOC (OVOC). NVOC emissions from oceans are estimated as a function of geophysical variables from a general circulation model and ocean color satellite data. Emissions from plant foliage are estimated from ecosystem specific biomass and emission factors and algorithms describing light and temperature dependence of NVOC emissions. Foliar density estimates are based on climatic variables and satellite data. Temporal variations in the model are driven by monthly estimates of biomass and temperature and hourly light estimates. The annual global VOC flux is estimated to be 1150 Tg C, composed of 44% isoprene, 11% monoterpenes, 22.5% other reactive VOC, and 22.5% other VOC. Large uncertainties exist for each of these estimates and particularly for compounds other than isoprene and monoterpenes. Tropical woodlands (rain forest, seasonal, drought-deciduous, and savanna) contribute about half of all global natural VOC emissions. Croplands, shrublands and other woodlands contribute 10–20% apiece. Isoprene emissions calculated for temperate regions are as much as a factor of 5 higher than previous estimates.

Inventorying emissions from nature in Europe

As part of the work of the Economic Commission for Europe of the United Nations Task Force on Emission Inventories, a new set of guidelines has been developed for assessing the emissions of sulphur, nitrogen oxides, NH3, CH4, and nonmethane volatile organic compounds (NMVOC) from biogenic and other natural sources in Europe. This paper gives the background to these guidelines, describes the sources, and gives our recommended methodologies for estimating emissions. We have assembled land use and other statistics from European or national compilations and present emission estimates for the various natural/biogenic source categories based on these. Total emissions from nature derived here amount to ∼1.1 Tg S yr−1, 6–8 Tg CH4 yr−1, 70 Gg NH3 (as N) yr−1, and 13 Tg NMVOC yr−1. Estimates of biogenic NO x emissions cover a wide range, from 140 to 1500 Gg NO x (as N) yr−1. In terms of relative contribution to total European emissions for different pollutants, then NMVOC from forests and vegetation are clearly the most important emissions source. Biogenic NO x emissions (although heavily influenced by nitrogen inputs from anthropogenic activities) are very important if the higher estimates are reliable. CH4 from wetlands and sulphur from volcanoes are also significant emissions in the European budgets. On a global scale, European biogenic emissions are not significant, a consequence of the climate and size (7% of global land area) of Europe and of the destruction of natural ecosystems since prehistoric times. However, for assessing local budgets and for photochemical oxidant modeling, natural/biogenic emissions can play an important role. The most important contributor in this regard is undoubtedly forest VOC emissions, although this paper also indicates that NMVOC emissions from nonforested areas also need to be further evaluated. This paper was originally conceived as a contribution to the collection of papers arising as a result of the Workshop on Biogenic Hydrocarbons in the Atmospheric Boundary Layer, August 24–27, 1997. (Several papers arising from this workshop have been published in Journal of Geophysical Research, 103(D19) 1998.)

Biogenic emissions in Europe: 1. Estimates and uncertainties

Several biogenic volatile organic compound (VOC) emission algorithms have been used, together with meteorological data from the EMEP MSC-W ozone model, to generate estimates of the emissions of isoprene from European forests and agricultural crops over several summer periods. The most up-to-date estimate combines the recently updated isoprene emission factors from the United States with available knowledge of European tree species and emission factors. In some cases these European emission factors are significantly different from their U.S. equivalents because of differences in the tree species represented within a forest classification, especially with regard to spruce genera and Mediterranean oak genera. The new estimates have resulted in an approximate factor of 2–3 increase in isoprene emissions from northern Europe but a factor of 2 decrease in isoprene estimates for southern Europe. Overall, European isoprene emissions are estimated to be about 4000 kt C yr−1, approximately 50–100% greater than previous estimates. Preliminary estimates are also made of the emissions of the so-called OVOC (other VOC) from forests and of soil NO x emissions. All of these estimates of biogenic emissions are subject to considerable uncertainty, not least because of a lack of knowledge of the species coverage in most European countries and of the appropriate emission factors which should be applied. Factors of 5–10 uncertainty are not unlikely for episodic ozone calculations. The implications of these uncertainties for the results of control strategy evaluations for rural ozone in Europe are assessed in a companion paper.

Isoprenoid emission of oak species typical for the Mediterranean area: source strength and controlling variables

Abstract Measurements of isoprenoid emission on five Mediterranean oak species in the field revealed that Quercus frainetto, Quercus petraea and Quercus pubescens are strong emitters of isoprene. In contrast Quercus cerris and Quercus suber emitted no significant amounts of isoprene and monoterpenes. For Q. pubenscens and Q. frainetto median emission factors of 16.68 nmol m −2 s −1 (86.06 μg g −1 dw h −1 ) and 30.72 nmol m −2 s −1 (133.95 μg g −1 dw h −1 were calculated, respectively. The 25 to 75 percentiles span of the emission factor data sets ranged from − 53% to + 56% of the median values. Light and temperature are the main controlling factors for isoprene emission. The influence of other environmental and plant physiological parameters on the isoprene emission is discussed. The “Guenther” emission algorithm is able to predict the daily maximum of the isoprene emission within the plant specific uncertainty range. However, the morning increase and the afternoon drop in the isoprene emission is not well parameterized. On the basis of process oriented models for the synthesis of isoprene in plants, a further reduction in the uncertainty may be achieved resulting in a more reliable prediction of short-time variation in isoprene emission.

Sampling and analysis of terpenes in air. An interlaboratory comparison

Abstract An interlaboratory comparison on the sampling and analysis of terpenes in air was held within the framework of the BEMA (Biogenic Emissions in the Mediterranean Area) project in May 1995. Samples were drawn and analysed by 10 European laboratories from a dynamic artificial air generator in which five terpenes were present at low ng l −1 levels and ozone varied between 8 and 125 ppbv. Significant improvements over previous inter-comparison exercises in the quality of results were observed. At the ozone mixing ratio of 8 ppbv a good agreement among laboratories was obtained for all test compounds with mean values close to the target concentration. At higher mixing ratios, ozone reduced terpene recoveries and decreased the precision of the measurements due to ozonolysis during sampling. For β-pinene this effect was negligible but for the more reactive compounds significant losses were observed in some laboratories ( cis -β-ocimene = trans -β-ocimene > linalool > d-limonene). The detrimental effect of ozone was significantly lower for the laboratories which removed ozone prior to sampling by scrubbers. Parallel sampling was carried out with a standardised sampler and each individual laboratorys own device. A good agreement between the two sets of results was obtained, clearly showing that the majority of laboratories used efficient sampling systems. Two different standard solutions were analysed by each laboratory. Only in a few cases did interference in the GC separation cause problems for the quantification of the terpenes (nonanal/linalool). However, making up of standards for the calibration of the analytical equipment (GC-MS or GC-FID) was pointed out as a source of error in some laboratories.

Global Organic Emissions from Vegetation

Organic emissions from vegetation are important inputs for global atmospheric chemistry models that simulate the processes controlling oxidant, CO, aerosol, and organic acid evolution, as well as the contribution of reactive carbon to global carbon cycles and budgets. Regional air quality policy decisions, which have large environmental and socio-economic impacts, also rely on correct natural organic emission estimates. The need for highly resolved and accurate organic emission estimates for air quality assessments in certain regions, particularly in the United States and parts of Europe, has led to recent improvements in methods for simulating emissions in these regions. Additional efforts in tropical landscapes have provided initial characterizations based on measurements whereas previous predictions were based on default assignments that treated most global landscapes in a similar manner.

Monoterpene synthase activities in leaves of Picea abies (L.) Karst. and Quercus ilex L.

In addition to direct ecological functions in the interaction of plants with the environment, the emission of monoterpenes, especially from the foliage of evergreen trees, is of great importance for the production of ozone and photochemical oxidants in the troposphere. In the present work, we established a reproducible non-radioactive standard enzyme assay and characterized monoterpene synthase activities in needles of Norway spruce (Picea abies (L.) Karst.) and in leaves of holm oak (Quercus ilex L.). In Norway spruce, the dominant monoterpenes formed were alpha-pinene, camphene, and to a lesser extent beta-pinene and limonene. In holm oak, alpha-pinene, sabinene, and beta-pinene were the main products, while limonene was a minor component. Under optimum conditions, in both Norway spruce and holm oak, monoterpene formation remained constant up to 180 min and 90 min, respectively, and varied with the buffer and Mg2+ and Mn2+ concentrations used. Optimum temperature for monoterpene synthase activity was 40 degrees C in both species; optimal pH ranged between 6.5 and 7.5 in both species. Apparent Michaelis-constants for the substrate GDP were ca. 17.9 +/- 5.1 microM for Norway spruce and ca. 69.4 +/- 22.1 microM for holm oak. Molecular weight determination by FPLC indicated that the monoterpene synthases in Norway spruce and holm oak have native molecular weights of ca. 59 and 50 kDa, respectively.

Biogenic emission from the Mediterranean pseudosteppe ecosystem present in Castelporziano

Emission rates and fluxes of biogenic components emitted by a Mediterranean Pseudosteppe were measured in the BEMA test site of Castelporziano during the 1993 and 1994 field campaigns. Enclosure and micrometeorological techniques were used. Although the emission was comprised of isoprene, semi-volatile aldehydes, acetic acid and monoterpenes at trace levels, the most relevant compound in air was isoprene. Basal emission rates for isoprene (normalized at 30°C and 1000 μE PAR) as defined by Guenther et al. (1991, J. geophys. Res. 96, 10,799–10,808) were obtained for this ecosystem by combining experimental observations and predictions based on the Guenther algorithm. It is shown that the Mediterranean Pseudosteppe is a strong isoprene emitter with a basal emission rate of 0.45 μg m−2 s−1 during the flowering season. At the end of the maximum physiologically active season basal emission rate ranged only in 0.1–0.15 μg m−2 s−1. A close dependence from light and temperature for the isoprene emission is observed. The decline in emission rates seems to be associated with a reduction in photosynthetic activity linked to senescence of the vegetation present in this ecosystem. The results obtained indicate that the Mediterranean Pseudosteppe is an ecosystem characterized by a rapid and strong variability in isoprene emission. It represents a source of isoprene comparable to deciduous forest areas only during the flowering season (from the middle of March to the middle of May) whereas it becomes a minor source during the end of the maximum physiologically active season.

Emission of Biogenic Volatile Organic Compounds: An Overview of Field, Laboratory and Modelling Studies Performed during the `Tropospheric Research Program' (TFS) 1997–2000

The present paper summarises results on the emission of biogenic volatile organic compounds (BVOC) achieved within the frame of the national ‘German Tropospheric Research Programme’ (TFS) between 1997 and 2000. Field measurements were carried out at the meteorological monitoring station ‘Hartheimer Wald’ located in the vicinity of Freiburg (upper Rhine valley), Germany, within a pine plantation dominated by Scots pine (Pinus sylvestris L.). The measured BVOC emission rates were used to determine the daily and seasonal variation of BVOC emission and its dependence on important meteorological and plant physiological parameters. In parallel, laboratory experiments using young trees of pine (P. sylvestris), poplar (Populus tremula × P. alba) and pedunculate oak (Quercus robur L.) were performed, and the influence of abiotic (e.g., light, temperature, seasonality, flooding) factors on the biosynthesis and emission of BVOC was quantified. Based on these data, emission algorithms were evaluated and a process-oriented numerical model for the simulation of the isoprene emission by plants was developed. In addition, newly calculated land use and tree species distributions were used for the calculation of an actual BVOC emission inventory of Germany.

Ambient atmospheric trace gas concentrations and meteorological parameters during the first BEMA measuring campaign on May 1994 at Castelporziano, Italy

Abstract During the first measuring campaign of the BEMA project, carried out in May 1994 at Castelporziano, near Rome, Italy, one of the tasks was to measure continuously meteorological parameters and tropospheric trace gas concentrations. The atmospheric species measured were ozone, NO x , anthropogenic and biogenic hydrocarbons, carbonyl compounds, hydrogen peroxide, organic peroxides and PAN. Another goal was the characterization of the atmospheric circulation patterns. The results showed that anthropogenic pollution is present at the Castelporziano site originating mainly from the Rome metropolitan area but also from other directions. The average concentration levels of NO x were about 9 ppb, the average total measured anthropogenic hydrocarbon concentration was 67 ppbC and the average ozone mixing ratio was 36 ppb. The possible role of naturally emitted VOCs in tropospheric ozone formation is discussed.