Measured isoprene emission rates of plants in California landscapes: comparison to estimates from taxonomic relationships

Isoprene emission rates of 64 plant species found in California's urban and natural landscapes were measured using a dynamic flow-through chamber enclosure technique. Species were selected to provide data for previously unmeasured species and to test estimates of isoprene emission rates based upon taxonomic relationships developed for compilation of biogenic emission inventories as proposed by Benjamin et al. (1996, Atmospheric Environment 30, 1437–1452). Branch-level isoprene emission rates ranged from undetectable for 47 species, to 54 μg g⁻¹ h⁻¹ for Quercus kelloggii, California black oak. Isoprene emission rate estimates based on taxonomy agreed well with our measurements for species within the same genus, with the exception of the Quercus genus for which a wide range of isoprene emission rates have been reported. As expected, family-level estimates based on taxonomy showed greater deviation from our measured values than did genus-based estimates. The data developed in the present study support use of a taxonomic predictive methodology, especially if previous measurements within specific families, sub-families, and genera are extensive, and the results of such assignment are treated with proper caution. A taxonomic approach may be most useful where plant species in natural and urban landscapes are numerous, such as in California, where no experimental measurements are available for thousands of species.     

Improved land cover and emission factors for modeling biogenic volatile organic compounds emissions from Hong Kong

This paper describes a study of local biogenic volatile organic compounds (BVOC) emissions from the Hong Kong Special Administrative Region (HKSAR). An improved land cover and emission factor database was developed to estimate Hong Kong emissions using MEGAN, a BVOC emission model developed by Guenther et al. (2006). Field surveys of plant species composition and laboratory measurements of emission factors were combined with other data to improve existing land cover and emission factor data. The BVOC emissions from Hong Kong were calculated for 12 consecutive years from 1995 to 2006. For the year 2006, the total annual BVOC emissions were determined to be 12,400 metric tons or 9.82 × 10⁹ g C (BVOC carbon). Isoprene emission accounts for 72%, monoterpene emissions account for 8%, and other VOCs emissions account for the remaining 20%. As expected, seasonal variation results in a higher emission in the summer and a lower emission in the winter, with emission predominantly in day time. A high emission of isoprene occurs for regions, such as Lowest Forest-NT North, dominated by broadleaf trees. The spatial variation of total BVOC is similar to the isoprene spatial variation due to its high contribution. The year to year variability in emissions due to weather was small over the twelve-year period (?1.4%, 2006 to 1995 trendline), but an increasing trend in the annual variation due to an increase in forest land cover can be observed (+7%, 2006 to 1995 trendline). The results of this study demonstrate the importance of accurate land cover inputs for biogenic emission models and indicate that land cover change should be considered for these models.     

A biogenic volatile organic compound emission inventory for Hong Kong

Biogenic volatile organic compounds (BVOCs) in the atmosphere react to form ozone and secondary organic aerosols, which deteriorate air quality, affect human health, and indirectly influence global climate changes. The present study aims to provide a preliminary assessment of BVOC emissions in Hong Kong (HKSAR). Thriteen local tree species were measured for their isoprene emission potential. Tree distribution was estimated for country park areas based on field survey data. Plant emission data obtained from measurements and the literature, tree distribution estimation data, land use information, and meteorological data were combined to estimate annual BVOC emissions of 8.6×10⁹ g C for Hong Kong. Isoprene, monoterpenes, and other VOCs contributed about 30%, 40%, and 30% of the estimated total annual emissions, respectively. Although hundreds of plant species are found in Hong Kong country parks, the model results indicate that only 10 tree species contribute about 76% of total annual VOC emissions. Prominent seasonal and diurnal variations in emissions were also predicted by the model. The present study lays a solid foundation for future local research, and results can be applied for studying BVOC emissions in nearby southern China and Asian regions that share similar climate and plant distributions.     

Approaches for quantifying reactive and low-volatility biogenic organic compound emissions by vegetation enclosure techniques - part B: applications

The focus of the studies presented in the preceding companion paper (Part A: Review) and here (Part B: Applications) is on defining representative emission rates from vegetation for determining the roles of biogenic volatile organic compound (BVOC) emissions in atmospheric chemistry and aerosol processes. The review of previously published procedures for identifying and quantifying BVOC emissions has revealed a wide variety of experimental methods used by various researchers. Experimental details become increasingly critical for quantitative emission measurements of low volatility monoterpenes (MT) and sesquiterpenes (SQT). These compounds are prone to be lost inadvertently by uptake to materials in contact with the sample air or by reactions with atmospheric oxidants. These losses become more prominent with higher molecular weight compounds, potentially leading to an underestimation of their emission rates. We present MT and SQT emission rate data from numerous experiments that include 23 deciduous tree species, 14 coniferous tree species, 8 crops, and 2 shrubs. These data indicate total, normalized (30 degrees C) basal emission rates from <10 to 5600ngCg(-1)h(-1) for MT, and from <10 to 1150ngCg(-1)h(-1) for SQT compounds. Both MT and SQT emissions have exponential dependencies on temperature (i.e. rates are proportional to e(betaT)). The inter-quartile range of beta-values for MT was between 0.12 and 0.17K(-1), which is higher than the value commonly used in models (0.09K(-1)). However many of the MT emissions also exhibited light dependencies, making it difficult to separate light and temperature influences. The primary light-dependent MT was ocimene, whose emissions were up to a factor of 10 higher than light-independent MT emissions. The inner-quartile range of beta-values for SQT was between 0.15 and 0.21K(-1).     

Tethered balloon measurements of biogenic VOCs in the atmospheric boundary layer

Biogenic volatile organic compounds (BVOCs) were measured on tethered balloon platforms in 11 deployments between 1985 and 1996. A series of balloon sampling packages have been used to describe boundary layer dynamics, BVOC distribution, chemical transformations of BVOCs, and to estimate BVOC emission rates from terrestrial vegetation. Measurements indicated a slow decrease of concentration for BVOCs with altitude in the mixed layer when sampling times were greater than average convective turnover time; surface layer concentrations were more variable because of proximity to various emission sources in the smaller surface layer footprint. Mixed layer concentrations of isoprene remained fairly constant in the middle of the day, in contrast to canopy-level isoprene concentrations, which continued to increase until early evening. Daytime emissions, which increase with temperature and light, appear to be balanced by changes in entrainment and oxidation. Daytime measurements of methacrolein and methyl vinyl ketone, reaction products of the atmospheric oxidation of isoprene, showed fairly constant ratio to each other with altitude throughout the mixed layer. BVOC emission flux estimates using balloon measurements and from the extrapolation of leaf level emissions to the landscape scale were in good agreement.     

Approaches for quantifying reactive and low-volatility biogenic organic compound emissions by vegetation enclosure techniques - part A

The high reactivity and low vapor pressure of many biogenic volatile organic compounds (BVOC) make it difficult to measure whole-canopy fluxes of BVOC species using common analytical techniques. The most appropriate approach for estimating these BVOC fluxes is to determine emission rates from dynamic vegetation enclosure measurements. After scaling leaf- and branch-level emission rates to the canopy level, these fluxes can then be used in models to determine BVOC influences on atmospheric chemistry and aerosol processes. Previously published reports from enclosure measurements show considerable variation among procedures with limited guidelines or standard protocols to follow. This article reviews this literature and describes the variety of enclosure types, materials, and analysis techniques that have been used to determine BVOC emission rates. The current review article is followed by a companion paper which details a comprehensive enclosure technique that incorporates both recommendations from the literature as well as insight gained from theoretical calculations and practical experiences. These methods have yielded new BVOC emission data for highly reactive monoterpenes (MT) and sesquiterpenes (SQT) from a variety of vegetation species.     

The tree BVOC index

Urban trees can produce a number of benefits, among them improved air quality. Biogenic volatile organic compounds (BVOCs) emitted by some species are ozone precursors. Modifying future tree planting to favor lower-emitting species can reduce these emissions and aid air management districts in meeting federally mandated emissions reductions for these compounds. Changes in BVOC emissions are calculated as the result of transitioning to a lower-emitting species mix in future planting. A simplified method for calculating the emissions reduction and a Tree BVOC index based on the calculated reduction is described. An example illustrates the use of the index as a tool for implementation and monitoring of a tree program designed to reduce BVOC emissions as a control measure being developed as part of the State Implementation Plan (SIP) for the Sacramento Federal Nonattainment Area.     

Temporal,spatial characteristics and uncertainty of biogenic VOC emissions in the Pearl River Delta region,China

Using the Global Biosphere Emissions and Interactions System model (GloBEIS), 3 × 3 km gridded and hourly biogenic volatile organic compound (BVOC) emissions in the Pearl River Delta (PRD) were estimated for the year 2006. The study used newly available land cover database, observed meteorological data, and recent measurements of emission rates for tree species in China. The results show that the total BVOC emission in the PRD region in 2006 was 296 kt (2.2 × 10¹¹ gC), of which isoprene contributes about 25% (73 kt, 6.4 × 10¹⁰ gC), monoterpenes about 34% (102 kt, 8.9 × 10¹⁰ gC), and other VOCs (OVOC) about 41% (121 kt, 6.8 × 10¹⁰ gC). BVOC emissions in the PRD region exhibit a marked seasonal pattern with the peak emission in July and the lowest emission in January, and are mainly distributed over the outlying areas of the PRD region, where the economy and land use are less developed. The uncertainties in BVOC emission estimates were quantified using Monte Carlo simulation; the results indicate high uncertainties in isoprene emission estimates, with a relative error of ?82 to +177%, ranging from 12.4 to 186.4 kt; ?41 to +58% uncertainty for monoterpenes emissions, ranging from 67.7 to 181.9 kt; and ?26 to +30% uncertainty in OVOC emissions, ranging from 88.8 to 156.2 kt on the 95% confidence intervals. The key uncertainty sources include emission factors and the model empirical coefficients α, C_T1, C_L, and E_opt for estimating isoprene emission, and emission factors and foliar density for estimating monoterpenes and OVOC emissions. This implies that determining these empirical coefficient values properly and conducting more field measurements of emission rates of tree species are key approaches for reducing uncertainties in BVOC emission estimates. Improving future BVOC emission inventory work in the PRD region requires giving priority to research on shrub land, coniferous forests, and irrigated cropland and pasture.     

A Fuel-Based Motor Vehicle Emission Inventory

Abstract

A fuel-based methodology for calculating motor vehicle emission inventories is presented. In the fuel-based method, emission factors are normalized to fuel consumption and expressed as grams of pollutant emitted per gallon of gasoline burned. Fleet-average emission factors are calculated from the measured on-road emissions of a large, random sample of vehicles. Gasoline use is known at the state level from sales tax data, and may be disaggregated to individual air basins. A fuel-based motor vehicle CO inventory was calculated for the South Coast Air Basin in California for summer 1991. Emission factors were calculated from remote sensing measurements of more than 70,000 in-use vehicles. Stabilized exhaust emissions of CO were estimated to be 4400 tons/day for cars and 1500 tons/day for light-duty and medium- duty trucks, with an estimated uncertainty of ±20% for cars and ±30% for trucks. Total motor vehicle CO emissions, including incremental start emissions and emissions from heavy-duty vehicles were estimated to be 7900 tons/day. Fuelbased inventory estimates were greater than those of California's MVEI 7F model by factors of 2.2 for cars and 2.6 for trucks. A draft version of California's MVEI 7G model, which includes increased contributions from high-emitting vehicles and off-cycle emissions, predicted CO emissions which closely matched the fuel-based inventory. An analysis of CO mass emissions as a function of vehicle age revealed that cars and trucks which were ten or more years old were responsible for 58% of stabilized exhaust CO emissions from all cars and trucks.     

Effect of vegetation removal and water table drawdown on the non-methane biogenic volatile organic compound emissions in boreal peatland microcosms

Biogenic volatile organic compound (BVOC) emissions are important in the global atmospheric chemistry and their feedbacks to global warming are uncertain. Global warming is expected to trigger vegetation changes and water table drawdown in boreal peatlands, such changes have only been investigated on isoprene emission but never on other BVOCs. We aimed at distinguishing the BVOCs released from vascular plants, mosses and peat in hummocks (dry microsites) and hollows (wet microsites) of boreal peatland microcosms maintained in growth chambers. We also assessed the effect of water table drawdown (?20 cm) on the BVOC emissions in hollow microcosms. BVOC emissions were measured from peat samples underneath the moss surface after the 7-week-long experiment to investigate whether the potential effects of vegetation and water table drawdown were shown. BVOCs were sampled using a conventional chamber method, collected on adsorbent and analyzed with GC–MS. In hummock microcosms, vascular plants increased the monoterpene emissions compared with the treatment where all above-ground vegetation was removed while no effect was detected on the sesquiterpenes, other reactive VOCs (ORVOCs) and other VOCs. Peat layer from underneath the surface with intact vegetation had the highest sesquiterpene emissions. In hollow microcosms, intact vegetation had the highest sesquiterpene emissions. Water table drawdown decreased monoterpene and other VOC emissions. Specific compounds could be closely associated to the natural/lowered water tables. Peat layer from underneath the surface of hollows with intact vegetation had the highest emissions of monoterpenes, sesquiterpenes and ORVOCs whereas water table drawdown decreased those emissions. The results suggest that global warming would change the BVOC emission mixtures from boreal peatlands following changes in vegetation composition and water table drawdown.     

Emissions of biogenic VOC from forest ecosystems in central Europe: Estimation and comparison with anthropogenic emission inventory

This paper describes a method of estimating emission fluxes of biogenic volatile organic compounds (BVOCs) based on the approach proposed by Guenther et al. (1995) and the high-resolution Corine land-cover 2000 database (1 × 1 km resolution). The computed emission fluxes for the Czech Republic (selected for analysis as being representative of a heavily cultivated, central European country) are compared with anthropogenic emissions, both for the entire country and for individual administrative regions. In some regions, BVOC emissions are as high as anthropogenic emissions; however, in most regions the BVOC emissions are approximately 50% of the anthropogenic emissions. The yearly course of BVOC emissions (represented by monoterpenes and isoprene) is presented, along with the spatial distribution of annual mean values. Differences in emission distributions during winter (January) and summer (June) are also considered.     

An Estimate of Biogenic Emissions of Volatile Organic Compounds during Summertime in China (7 pp)

Background and Aim An accurate estimation of biogenic emissions of VOC (volatile organic compounds) is necessary for better understanding a series of current environmental problems such as summertime smong and global climate change. However, very limited studies have been reported on such emissions in China. The aim of this paper is to present an estimate of biogenic VOC emissions during summertime in China, and discuss its uncertainties and potential areas for further investigations. Materials and Methods This study was mainly based on field data and related research available so far in China and abroad, including distributions of land use and vegetations, biomass densities and emission potentials. VOC were grouped into isoprene, monoterpenes and other VOC (OVOC). Emission potentials of forests were determined for 22 genera or species, and then assigned to 33 forest ecosystems. The NCEP/NCAR reanalysis database was used as standard environmental conditions. A typical summertime of July 1999 was chosen for detailed calculations. Results and Discussion The biogenic VOC emissions in China in July were estimated to be 2.3×10¹²gC, with 42% as isoprene, 19% as monoterpenes and 39% as OVOC. About 77.3% of the emissions are generated-from forests and woodlands. The averaged emission intensity was 4.11 mgC m⁻² hr⁻¹ for forests and 1.12 mgC m⁻² hr⁻¹ for all types of vegetations in China during the summertime. The uncertainty in the results arose from both the data and the assumptions used in the extrapolations. Generally, uncertainty in the field measurements is relatively small. A large part of the uncertainty mainly comes from the taxonomic method to assign emission potentials to unmeasured species, while the ARGR method serves to estimate leaf biomass and the emission algorithms to describe light and temperature dependence. Conclusions This study describes a picture of the biogenic VOC emissions during summertime in China. Due to the uneven spatial and temporal distributions, biogenic VOC emissions may play an important role in the tropospheric chemistry during summertime. Recommendations and Perspectives Further investigations are needed to reduce uncertainties involved in the related factors such as emission potentials, leaf biomass, species distribution as well as the mechanisms of the emission activities. Besides ground measurements, attention should also be placed on other techniques such as remotesensing and dynamic modeling. These new approaches, combined with ground measurements as basic database for calibration and evaluation, can hopefully provide more comprehensive information in the research of this field. Submission Editor: Prof. Dr. Gerhard Lammel (lammel@recetox.muni.cz)     

Seasonal variations of monoterpene emissions from coniferous trees of different ages in Korea

Seasonal variations of emission rates and compositions from coniferous species were measured under controlled conditions using a vegetation enclosure method. Total emission rates and compositions of monoterpene compounds from young and adult trees in different seasons were compared.

It was found that the total emission rates and the components of monoterpene varied significantly with tree species, age, and season. Total emissions from C. japonica and P. koraiensis were higher for older trees than for younger trees; however, significantly higher emissions were found from younger trees for C. obtusa. Higher monoterpene emission rates from each plant were found in spring and summer compared with autumn and winter emissions.     

Seasonal monoterpene and sesquiterpene emissions from Pinus taeda and Pinus virginiana

Seasonal volatile organic compound emission data from loblolly pine (Pinus taeda) and Virginia pine (Pinus virginiana) were collected using branch enclosure techniques in Central North Carolina, USA. P. taeda monoterpene emission rates were at least ten times higher than oxygenated monoterpene and sesquiterpene emissions in all seasons. α-pinene and β-pinene were the most abundant emissions, while β-caryophyllene had the highest sesquiterpene emission rate from this species. β-phellandrene was the dominant compound emitted from P. virginiana, followed by the sesquiterpene β-caryophyllene. Sesquiterpene emissions from P. virginiana have not been reported in the literature previously. Summer sesquiterpene emissions from P. virginiana were nearly as high as monoterpene emissions, but were 4–12 times lower than monoterpene emissions in the other seasons. Oxygenated monoterpenes and 2-methyl-3-buten-2-ol were emitted at higher rates from P. taeda than from P. virginiana. Temperature response of the pinenes from P. taeda is similar to previously reported values used in emission models, while that for other compounds falls at the lower end of the previously reported range. Temperature response of all compounds from P. virginiana is in reasonable agreement with previously reported values from other pine species. There is evidence of light dependence of sesquiterpene emission after accounting for temperature response from both species. This effect is somewhat stronger in P. taeda. Bud break, needle expansion, and needle fall (and therefore wind events) seemed to increase monoterpene emission during non-summer seasons. In some instances springtime monoterpene emissions were higher than summertime emissions despite cooler temperatures. Emissions of individual compounds within monoterpene, oxygenated monoterpene, and sesquiterpene classes were highly correlated with each other. Compounds from different classes were much less correlated within each species. This is due to a varying temporal emission patterns for each BVOC class and suggests different production, storage, and emission controls for each. Analysis of enclosure blanks and diurnal patterns indicates that, despite precautions, disturbance due to the enclosure technique may still impact monoterpene emission rate estimates. This did not appear to affect sesquiterpene emissions.     

Intra- and inter-annual variability of VOC emissions from natural and semi-natural vegetation in Europe and neighbouring countries

Biogenic VOC emission estimates from the earth's surface are crucial input parameters in air quality models. Knowledge accumulated in the last years about BVOC source distributions and chemical compound species emission profiles in Europe as well as the demand of air quality modellers for a finer resolution in space and time of BVOC estimates have led to the set-up of new emission modelling systems. An updated fast BVOC emission modelling platform explicitly considering the seasonality of emission potentials and leaf temperature gradients in forest canopies by the semi-empirical emission module (seBVOC) will be proposed and used for estimating hourly values of chemical compound-specific emissions in Europe (33–68° north; 10° west to 40° east) in the years 1997, 2000, 2001, and 2003. Spatial resolution will be 10 km by 10 km. The database used contains latest land and forest distributions, updated foliar biomass densities, leaf area indices (LAI), and plant as well as chemical compound-specific emission potentials, if available. Meteorological input parameters for the respective years will be generated using the non-hydrostatic meteorological model MM5. Highest BVOC emissions occur in daytime hours around noon from the end of May to mid-August in the Mediterranean area and from the mid of June to the end of July in the boreal forests. Comparison of 3 BVOC model approaches will reveal that for July 2003, the European isoprene and monoterpene totals range from 1124 Gg to 1446 Gg and from 338 Gg to 1112 Gg, respectively. Small-scale deviations may be as high as ±0.6 Mg km^?2 for July 2003, reflecting the current uncertainty range for BVOC estimates. Key sources of errors in inventories are still insufficiently detailed land use data for some areas and lacking chemically speciated plant-specific emission potentials in particular in boreal, south-eastern, and northern African landscapes. The hourly emissions of isoprene, speciated terpenes, and oxyVOC have been made available by the NatAir database.     

Modeling the influence of biogenic volatile organic compound emissions on ozone concentration during summer season in the Kinki region of Japan

Tropospheric ozone adversely affects human health and vegetation, and biogenic volatile organic compound (BVOC) emission has potential to influence ozone concentration in summer season. In this research, the standard emissions of isoprene and monoterpene from the vegetation of the Kinki region of Japan, estimated from growth chamber experiments, were converted into hourly emissions for July 2002 using the temperature and light intensity data obtained from results of MM5 meteorological model. To investigate the effect of BVOC emissions on ozone production, two ozone simulations for one-month period of July 2002 were carried out. In one simulation, hourly BVOC emissions were included (BIO), while in the other one, BVOC emissions were not considered (NOBIO). The quantitative analyses of the ozone results clearly indicate that the use of spatio-temporally varying BVOC emission improves the prediction of ozone concentration. The hourly differences of monthly-averaged ozone concentrations between BIO and NOBIO had the maximum value of 6 ppb at 1400 JST. The explicit difference appeared in urban area, though the place where the maximum difference occurred changed with time. Overall, BVOC emissions from the forest vegetation strongly affected the ozone generation in the urban area.     

Biogenic volatile organic compound emissions from a lowland tropical wet forest in Costa Rica

Twenty common plant species were screened for emissions of biogenic volatile organic compounds (BVOCs) at a lowland tropical wet forest site in Costa Rica. Ten of the species examined emitted substantial quantities of isoprene. These species accounted for 35–50% of the total basal area of old-growth forest on the major edaphic site types, indicating that a high proportion of the canopy leaf area is a source of isoprene. A limited number of canopy-level BVOC flux measurements were also collected by relaxed eddy accumulation (REA). These measurements verify that the forest canopy in this region is indeed a significant source of isoprene. In addition, REA fluxes of methanol and especially acetone were also significant, exceeding model estimates and warranting future investigation at this site. Leaf monoterpene emissions were non-detectable or very low from the species surveyed, and ambient concentrations and REA fluxes likewise were very low. Although the isoprene emission rates reported here are largely consistent with phylogenetic relations found in other studies (at the family, genus, and species levels), two species in the family Mimosaceae, a group previously found to consist largely of non-isoprene emitters, emitted significant quantities of isoprene. One of these, Pentaclethra macroloba (Willd.) Kuntze, is by far the most abundant canopy tree species in the forests of this area, composing 30–40% of the total basal area. The other, Zygia longifolia (Humb. & Bonpl.) Britton & Rose is a common riparian species. Our results suggest that the source strength of BVOCs is important not only to tropical atmospheric chemistry, but also may be important in determining net ecosystem carbon exchange.     

CH4 and N2O emissions from Spartina alterniflora and Phragmites australis in experimental mesocosms

Spartina alterniflora, a perennial grass with C(4)-photosynthesis, shows great invading potential in the coastal ecosystems in the east of China. We compared trace gas emissions from S. alterniflora with those from a native C(3) plant, Phragmites australis, by establishing brackish marsh mesocosms to experimentally assess the effects of plant species (S. alterniflora vs. P. australis), flooding status (submerged vs. non-submerged), and clipping (plants clipped or not) on trace gas emissions. The results show that trace gas emission rates were higher in S. alterniflora than P. australis mesocosms due to the higher biomass and density of the former, which could fix more available substrates to the soil and potentially emit more trace gases. Meanwhile, trace gas emission rates were higher in non-submerged than submerged soils, suggesting that water might act as a diffusion barrier in the brackish marsh mesocosms. Interestingly, methane (CH(4)) emission rates were lower in clipped non-submerged mesocosms than in non-clipped submerged mesocosms, but nitrous oxide (N(2)O) emissions were enhanced. CH(4) emissions were significantly correlated with the plant biomass and stem density (R(2)>0.48, P<0.05) for both species, suggesting that both the two species might play important roles in CH(4) production and transport and also act as suppliers of easily available substrates for the methanogenic bacteria in wetland ecosystems. N(2)O emissions, however, were not significantly correlated with plant biomass and density (P>0.05).     

Secondary organic aerosol importance in the future atmosphere

In order to investigate the secondary organic aerosol (SOA) response to changes in biogenic volatile organic compounds (VOC) emissions in the future atmosphere and how important will SOA be relative to the major anthropogenic aerosol component (sulfate), the global three-dimensional chemistry/transport model TM3 has been used. Emission estimates of biogenic VOC (BVOC) and anthropogenic gases and particles from the literature for the year 2100 have been adopted.According to our present-day model simulations, isoprene oxidation produces 4.6 Tg SOA yr⁻¹, that is less than half of the 12.2 Tg SOA yr⁻¹ formed by the oxidation of other BVOC. In the future, nitrate radicals and ozone become more important than nowadays, but remain minor oxidants for both isoprene and aromatics. SOA produced by isoprene is estimated to almost triple, whereas the production from other BVOC more than triples. The calculated future SOA burden change, from 0.8 Tg at present to 2.0 Tg in the future, is driven by changes in emissions, oxidant levels and pre-existing particles. The non-linearity in SOA formation and the involved chemical and physical feedbacks prohibit the quantitative attribution of the computed changes to the above-mentioned individual factors. In 2100, SOA burden is calculated to exceed that of sulfate, indicating that SOA might become more important than nowadays. These results critically depend on the biogenic emissions and thus are subject to the high uncertainty associated with these emissions estimated due to the insufficient knowledge on plant response to carbon dioxide changes. Nevertheless, they clearly indicate that the change in oxidants and primary aerosol caused by human activities can contribute as much as the change in BVOC emissions to the increase of the biogenic SOA production in the future atmosphere.     

Transient analysis of volatile organic compound concentrations for estimating emission rates

While emission rates of volatile organic compounds (VOCs) have been obtained for building materials, furnishings and processes in chambers, field measurements are more difficult. Procedures to estimate emission rates using transient analysis of VOC concentrations are described and applied in a two-story classroom/office building. The analysis employs semi-real-time VOC concentrations determined with a portable GC/FID and simultaneous air change rate measurements using tracer gas decay. The results of the analysis yield consistent values of emission rates for building materials ranging from 0.20 to 0.40 mg m⁻² h⁻¹ when normalized by floor area. Occupancy-related emissions were more difficult to estimate and covered a wider range from roughly 0.1 to 1.5 mg m⁻² h⁻¹. The test data were also analyzed in an attempt to determine sink parameters, but these efforts were not particularly successful. Furthermore, in these tests, the inclusion of sink effects did not significantly impact the estimated emission rates. While this paper offers a transient analysis approach that may lead to improved field estimates of VOC emission rates, it is not presented as a definitive methodology. Nevertheless, transient analysis has potential for use in other buildings, but simultaneous air change rate measurements are critical in its application in estimating VOC emission rates in the field.