Global Biogenic Emissions Research Articles

Seasonal variations in whole-ecosystem BVOC emissions from a subtropical bamboo plantation in China

Abstract Isoprene and monoterpene emissions and environmental conditions were measured over a six month period in a Lei bamboo (Phyllostachys violascens) forest in a subtropical region in China. Isoprene and monoterpene emissions were measured using a relaxed eddy accumulation (REA) system on an above-canopy tower. From July to November of 2012, isoprene contributed 99.1% of terpenoid emissions. α-pinene, constituting 0.8% of total observed terpenoid emissions, was the only monoterpene for which a significant flux was detected. Emissions of the sesquiterpenes longifolene and α-cedrene were observed at very low rates. Isoprene and α-pinene emissions exhibited strong diurnal variations, with lower emissions in the morning and late evening, and the highest emissions around noon. BVOC peak emissions typically occurred a few hours after the noon PAR peak and coincided with the daily temperature peak. This behavior can be described reasonably well by the MEGANv2.1 biogenic emission model. During the campaign (i.e., from 7 July, 2012 to 19 Jan., 2013), the mean (and maximum) emission fluxes (mg m −2 h −1 ) were 0.95 (10.32) for isoprene, 0.010 (0.176) for α pinene, 0.001 (0.063) for longifolene, and 2.6 × 10 −4 (0.009) for α-cedrene, respectively. During the winter season, when the ground was covered by organic mulch to increase soil temperature and to increase the yield of bamboo shoot, there was no evident impact on BVOC emissions. The observed seasonal variation followed the general behavior predicted by the MEGANv2.1 model, with lower emissions associated with cooler conditions, but the magnitude of the emission decrease was greater than expected indicating driving variables are missing from the model. Emission factors, representing the emission expected for a Leaf Area Index of 5 at a temperature of 30 °C and PAR of 1500 μmol m −2 s −1 , during the peak growing season for this site were 0.008 mg m −2 h −1 for α-pinene and 3.3 mg m −2 h −1 for isoprene. The isoprene emission factor is similar to the value (3.6 mg m −2 h −1 ) for this location in the MEGANv2.1 global biogenic emission model. A second bamboo plantation, containing Moso bamboo ( Phyllostachys heterocycla ), was investigated and found to have similar isoprene and monoterpene emission rates as Lei bamboo forest. The emission data obtained in this study are the first canopy-scale flux measurements reported for bamboo plantations and demonstrate the potential importance of bamboo isoprene emissions for regional ozone and organic aerosol production.

WRF-CMAQ 모델을 이용한 한반도 CH4배출의 기여농도 추정 및 검증

이 연구의 목적은 한반도에서 <TEX>$CH_4$</TEX> 농도의 수치모의 검증을 통하여 <TEX>$CH_4$</TEX> 배출원의 기여 농도를 추정하는 것이고, 이 수치모의에 사용된 <TEX>$CH_4$</TEX> 배출량을 상자모델로부터 추정된 <TEX>$CH_4$</TEX> 배출량과 비교하는 것이다. 한반도에서 2010년 4월 1일부터 8월 22일까지 <TEX>$CH_4$</TEX>의 평균 농도를 추정하기 위해 WRF-CMAQ 모델이 사용되었다. 모델에서 <TEX>$CH_4$</TEX> 배출량은 전지구 배출량인 EDGAR와 한국에서의 온실기체 배출량인 GHG-CAPSS로부터 인위적 배출 인벤토리와 전지구 자연적 인벤토리인 MEGAN이 적용되었다. 이들 <TEX>$CH_4$</TEX> 배출량은 안면도 및 울릉도에서 측정된 <TEX>$CH_4$</TEX> 농도와 모델링 농도 자료를 비교함으로써 검증되었다. 울릉도에서 국내 배출원으로부터 추정된 <TEX>$CH_4$</TEX>의 기여 농도는 약 20%로 나타났고, 이것은 한반도 내 농장(8%), 에너지 기여 및 산업공정(6%), 일반폐기물(5%), 생체 및 토지이용(1%) 등 <TEX>$CH_4$</TEX> 배출원으로부터 기원하였다. 그리고 중국으로부터 수송된 <TEX>$CH_4$</TEX>의 기여 농도는 약 9%였고, 나머지 배경농도는 약 70%로 나타났다. 박스모델로 추정된 <TEX>$CH_4$</TEX> 배출량은 WRF-CMAQ 모델에서 사용한 <TEX>$CH_4$</TEX> 배출량과 유의미한 결과를 얻었다. The purpose of this study was to estimate the contributed concentration of each emission source to <TEX>$CH_4$</TEX> by verifying the simulated concentration of <TEX>$CH_4$</TEX> in the Korean peninsula, and then to compare the <TEX>$CH_4$</TEX> emission used to the <TEX>$CH_4$</TEX> simulation with that of a box model. We simulated the Weather Research Forecasting-Community Multiscale Air Quality (WRF-CMAQ) model to estimate the mean concentration of <TEX>$CH_4$</TEX> during the period of April 1 to 22 August 2010 in the Korean peninsula. The <TEX>$CH_4$</TEX> emissions within the model were adopted by the anthropogenic emission inventory of both the EDGAR of the global emissions and the GHG-CAPSS of the green house gases in Korea, and by the global biogenic emission inventory of the MEGAN. These <TEX>$CH_4$</TEX> emission data were validated by comparing the <TEX>$CH_4$</TEX> modeling data with the concentration data measured at two different location, Ulnungdo and Anmyeondo in Korea. The contributed concentration of <TEX>$CH_4$</TEX> estimated from the domestic emission sources in verification of the <TEX>$CH_4$</TEX> modeling at Ulnungdo was represented in about 20%, which originated from <TEX>$CH_4$</TEX> sources such as stock farm products (8%), energy contribution and industrial processes (6%), wastes (5%), and biogenesis and landuse (1%) in the Korean peninsula. In addition, one that transported from China was about 9%, and the background concentration of <TEX>$CH_4$</TEX> was shown in about 70%. Furthermore, the <TEX>$CH_4$</TEX> emission estimated from a box model was similar to that of the WRF-CMAQ model.

Quantifying the uncertainty in simulating global tropospheric composition due to the variability in global emission estimates of Biogenic Volatile Organic Compounds

Abstract. The emission of organic compounds from biogenic processes acts as an important source of trace gases in remote regions away from urban conurbations, and is likely to become more important in future decades due to the further mitigation of anthropogenic emissions that affect air quality and climate forcing. In this study we examine the contribution of biogenic volatile organic compounds (BVOCs) towards global tropospheric composition using the global 3-D chemistry transport model TM5 and the recently developed modified CB05 chemical mechanism. By comparing regional BVOC emission estimates we show that biogenic processes act as dominant sources for many regions and exhibit a large variability in the annually and seasonally integrated emission fluxes. By performing sensitivity studies we find that the contribution of BVOC species containing between 1 to 3 carbon atoms has an impact on the resident mixing ratios of tropospheric O3 and CO, accounting for ~2.5% and ~10.8% of the simulated global distribution, respectively. This is approximately a third of the cumulative effect introduced by isoprene and the monoterpenes. By examining an ensemble of 3-D global chemistry transport simulations which adopt different global BVOC emission inventories we determine the associated uncertainty introduced towards simulating the composition of the troposphere for the year 2000. By comparing the model ensemble values against a composite of atmospheric measurements we show that the effects on tropospheric O3 are limited to the lower troposphere (with an uncertainty between −2% to 10%), whereas that for tropospheric CO extends up to the upper troposphere (with an uncertainty of between 10 to 45%). Comparing the mixing ratios for low molecular weight alkenes in TM5 against surface measurements taken in Europe implies that the cumulative emission estimates are too low, regardless of the chosen BVOC inventory. This variability in the global distribution of CO due to BVOC emissions introduces an associated uncertainty in the tropospheric CO burden of 11.4%, which impacts strongly on the oxidative capacity of the troposphere, introducing an uncertainty in the atmospheric lifetime of the greenhouse gas CH4 of ~3.3%. This study thus identifies the necessity of placing further constraints on non-CH4 global biogenic emission estimates in large-scale global atmospheric chemistry models.

Evaluation of two isoprene emission models for use in a long-range air pollution model

Abstract. Knowledge about isoprene emissions and concentration distribution is important for chemistry transport models (CTMs), because isoprene acts as a precursor for tropospheric ozone and subsequently affects the atmospheric concentrations of many other atmospheric compounds. Isoprene has a short lifetime, and hence it is very difficult to evaluate its emission estimates against measurements. For this reason, we coupled two isoprene emission models with the Danish Eulerian Hemispheric Model (DEHM), and evaluated the simulated background ozone concentrations based on different models for isoprene emissions. In this research, results of using the two global biogenic emission models; GEIA (Global Emissions Inventory Activity) and MEGAN (the global Model of Emissions of Gases and Aerosols from Nature) are compared and evaluated. The total annual emissions of isoprene for the year 2006 estimated by using MEGAN is 592 Tg yr−1 for an extended area of the Northern Hemisphere, which is 21% higher than that estimated by using GEIA. The overall feature of the emissions from the two models is quite similar, but differences are found mainly in Africa's savannah and in the southern part of North America. Differences in spatial distribution of emission factors are found to be a key source of these discrepancies. In spite of the short life-time of isoprene, a direct evaluation of isoprene concentrations using the two biogenic emission models in DEHM has been made against available measurements in Europe. Results show an agreement between two models simulations and the measurements in general and that the CTM is able to simulate isoprene concentrations. Additionally, investigation of ozone concentrations resulting from the two biogenic emission models show that isoprene simulated by MEGAN strongly affects the ozone production in the African savannah; the effect is up to 10% more than that obtained using GEIA. In contrast, the impact of using GEIA is higher in the Amazon region with more than 8% higher ozone concentrations compared to that of using MEGAN. Comparing the ozone concentrations obtained by DEHM using the two different isoprene models with measurements from Europe and North America, show an agreement on the hourly, mean daily and daily maximum values. However, the average of ozone daily maximum value simulated by using MEGAN is slightly closer to the measured value for the average of all measuring sites in Europe.

The Regional Biogenic Emissions Response to Climate Changes and Ambient CO₂ in Southeast Asia

The emissions of isoprene from vegetation in the tropics have been regarded as one of the major sources of the global biogenic emission budget. As this emission is highly sensitive to temperature, one may expect significant changes to the emissions due to climate change. In this study, we explore the impact of regional climate change to the emissions of isoprene in Southeast Asia. The potential role of the combination of climate change and future atmospheric CO₂ concentration on isoprene emissions are also investigated. The latest generation of Hadley Centre regional climate modelling system, PRECIS (Providing Regional Climates for Impact Studies) was used to investigate the climate change in the region. The climate output dataset from the model was then used as input for the BVOC Emission Model, which was developed by Sheffield University and Lancaster University to estimate the emissions of biogenic volatile organic compounds. The projected temperature changes under the A₂ emission scenario was 2.5⁰C, which accounted an increase of 22% of isoprene emission from 29 to 37 TgC/yr if the CO₂ emission factor was excluded. Incorporation of higher concentration in future CO₂ emissions was found to offset the climate change impact on future emissions of isoprene in the region. With the CO₂ effects, the projected regional isoprene emissions in 2100 dropped from 28 to 25 TgC/yr. These results suggest that future emissions of isoprene in the region is largely buffered by a number of competing factors, which are certainly important to be considered in estimating the isoprene global budget. In a wider perspective, the anticipated high concentration of CO₂ in the future could lead to the disruption of the ozone, organic aerosol and methane formation through the competing influence with warmer climate on isoprene emissions from tropical vegetation.

A review of Secondary Organic Aerosol (SOA) formation from isoprene

Abstract. Recent field and laboratory evidence indicates that the oxidation of isoprene, (2-methyl-1,3-butadiene, C5H8) forms secondary organic aerosol (SOA). Global biogenic emissions of isoprene (600 Tg yr−1) are sufficiently large that the formation of SOA in even small yields results in substantial production of atmospheric particulate matter, likely having implications for air quality and climate. Here we present a review of field measurements, experimental work, and modeling studies aimed at understanding the mechanisms, yield, and atmospheric importance of isoprene-derived SOA. SOA yields depend on a number of factors, including organic aerosol loading (Mo), NOx level (RO2 chemistry), and, because of the importance of multigenerational chemistry, the degree of oxidation. These dependences are not always included in SOA modules used in atmospheric transport models, and instead most yield parameterizations rely on a single set of chamber experiments (carried out over a limited range of conditions); this may lead to very different estimates of the atmospheric importance of isoprene SOA. New yield parameterizations, based on all available laboratory data (Mo=0–50 μg m−3), are presented here, so that SOA formation may be computed as a function of Mo, NOx level, and temperature. Current research needs and future research directions are identified.

Impact of climate variability and land use changes on global biogenic volatile organic compound emissions

Abstract. A biogenic emissions scheme has been incorporated in the global dynamic vegetation model ORCHIDEE (Organizing Carbon and Hydrology in Dynamic EcosystEms) in order to calculate global biogenic emissions of isoprene, monoterpenes, methanol, acetone, acetaldehyde, formaldehyde and formic and acetic acids. Important parameters such as the leaf area index are fully determined by the global vegetation model and the influences of light extinction (for isoprene emissions) and leaf age (for isoprene and methanol emissions) are also taken into account. We study the interannual variability of biogenic emissions using the satellite-based climate forcing ISLSCP-II as well as relevant CO2 atmospheric levels, for the 1983–1995 period. Mean global emissions of 460 TgC/yr for isoprene, 117 TgC/yr for monoterpenes, 106 TgC/yr for methanol and 42 TgC/yr for acetone are predicted. The mean global emission of all biogenic compounds is 752±16 TgC/yr with extremes ranging from 717 TgC/yr in 1986 to 778 TgC/yr in 1995, that is a 8.5% increase between both. This variability differs significantly from one region to another and among the regions studied, biogenic emissions anomalies were the most variable in Europe and the least variable in Indonesia (isoprene and monoterpenes) and North America (methanol). Two scenarios of land use changes are considered using the 1983 climate and atmospheric CO2 conditions, to study the sensitivity of biogenic emissions to vegetation alteration, namely tropical deforestation and European afforestation. Global biogenic emissions are highly affected by tropical deforestation, with a 29% decrease in isoprene emission and a 22% increase in methanol emission. Global emissions are not significantly affected by European afforestation, but on a European scale, total biogenic VOCs emissions increase by 54%.

Modeling of global biogenic emissions for key indirect greenhouse gases and their response to atmospheric CO2 increases and changes in land cover and climate

Natural emissions of nonmethane volatile organic compounds (NMVOCs) play a crucial role in the oxidation capacity of the lower atmosphere and changes in concentrations of major greenhouse gases (GHGs), particularly methane and tropospheric ozone. In this study, we integrate a global biogenic model within a terrestrial ecosystem model to investigate the vegetation and soil emissions of key indirect GHGs, e.g., isoprene, monoterpene, other NMVOCs (OVOC), CO, and NOx. The combination of a high‐resolution terrestrial ecosystem model with satellite data allows investigation of the potential changes in net primary productivity (NPP) and resultant biogenic emissions of indirect GHGs due to atmospheric CO2 increases and changes in climate and land use practices. Estimated global total annual vegetation emissions for isoprene, monoterpene, OVOC, and CO are 601, 103, 102, and 73 Tg C, respectively. Estimated NOx emissions from soils are 7.51 Tg N. The land cover changes for croplands generally lead to a decline of vegetation emissions for isoprene OVOC, whereas temperature and atmospheric CO2 increases lead to higher vegetation emissions. The modeled global mean isoprene emissions show relatively large seasonal variations over the previous 20 years from 1981 to 2000 (as much as 31% from year to year). Savanna and boreal forests show large seasonal variations, whereas tropical forests with high plant productivity throughout the year show small seasonal variations. Results of biogenic emissions from 1981 to 2000 indicate that the CO2 fertilization effect, along with changes in climate and land use, causes the overall up‐trend in isoprene and OVOC emissions over the past 2 decades. This relationship suggests that future emission scenario estimations for NMVOCs should account for effects of CO2 and climate in order to more accurately estimate local, regional, and global chemical composition of the atmosphere, the global carbon budget, and radiation balance of the Earth‐atmosphere system.

Past and future changes in biogenic volatile organic compound emissions simulated with a global dynamic vegetation model

Based on an interactive global biogenic emission and dynamic vegetation model, we investigate the evolution of volatile organic compound (VOC) emissions by the terrestrial biosphere in four scenarios: the Last Glacial Maximum (21,000 years BP), the preindustrial (1850s), present‐day (1990s) and the future (2100). The combined effects of foliar expansion, climate change and ecosystems redistribution impact strongly on biogenic emissions. Total biogenic VOC emissions increase from 331 TgC/yr at the LGM to 702 TgC/yr at the preindustrial, 725 TgC/yr at present‐day and to 1251 TgC/yr under future conditions. If the tropics remain a major source region, a substantial decrease in VOC emissions is calculated over Amazonia for 2100 due to the recession of tropical forests in response to climate change. The Northern Hemisphere becomes a significant source of VOC in the future and globally, emissions increase by 27% for isoprene and 51% for monoterpenes compared to the present.

Estimation of biogenic volatile organic compounds emissions in subtropical island—Taiwan

Elevated tropospheric ozone is harmful to human health and plants. It is formed through the photochemical reactions involving volatile organic compounds (VOCs) and nitrogen oxides (NO x ). The elevated ozone episodes occur mainly in summer months in the United States, while the high-ozone episodes frequently occur during the fall in Taiwan. The unique landscape of Taiwan produces tremendous amounts of biogenic VOCs in the mountain regions that are adjacent to concentrated urban areas. The urban areas, in turn, generate prodigious amounts of anthropogenic emissions. Biogenic VOC emissions have direct influence on tropospheric ozone formation. To explore the air quality problems in Taiwan, this study attempts to develop a biogenic VOC emission model suitable for air quality applications in Taiwan. The emission model is based on the Biogenic Emissions Inventory System Version 2 and coupled with a detailed Taiwan land use database. The 1999 total Taiwan biogenic VOC emissions were estimated at 214,000 metric tons. The emissions of isoprene, monoterpenes, and other VOCs were about 37.2%, 30.4%, and 32.4% of total biogenic VOC emissions, respectively. The annual total biogenic VOC emission per unit area was more than two times the value of that in any European country, implying that detailed emissions estimates in any size of region will benefit the global biogenic emission inventories.