Missing ozone-induced potential aerosol formation in a suburban deciduous forest
Tomoki NakayamaYuki KurumaYutaka MatsumiYu MorinoKei SatoHiroshi TsurumaruSathiyamurthi RamasamyYosuke SakamotoShunsuke KatoYuzo MiyazakiTomoki MochizukiKimitaka KawamuraYasuhiro SadanagaYoshihiro NakashimaKazuhide MatsudaYoshizumi Kajii
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Isoprene
Noon
Volatile organic compound
Particle (ecology)
Atmospheric chemistry
Isoprene
Atmospheric chemistry
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We have implemented a process‐based isoprene emission model in the HadGEM2 Earth‐system model with coupled atmospheric chemistry in order to examine the feedback between isoprene emission and climate. Isoprene emissions and their impact on atmospheric chemistry and climate are estimated for preindustrial (1860–1869), present‐day (2000–2009), and future (2100–2109) climate conditions. The estimate of 460 TgC/yr for present‐day global total isoprene emission is consistent with previous estimates. Preindustrial isoprene emissions are estimated to be 26% higher than present‐day. Future isoprene emissions using the RCP8.5 scenario are similar to present‐day because increased emissions resulting from climate warming are countered by CO 2 inhibition of isoprene emissions. The impact of biogenic isoprene emissions on the global O 3 burden and CH 4 lifetime is small but locally significant, and the impact of changes in isoprene emissions on atmospheric chemistry depends strongly on the state of climate and chemistry.
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Abstract. Biogenic volatile organic compounds (BVOCs) such as isoprene constitute a large proportion of the global atmospheric oxidant sink. Their reactions in the atmosphere contribute to processes such as ozone production and secondary organic aerosol formation. However, over the tropical rainforest, where 50% of the global emissions of BVOCs are believed to occur, atmospheric chemistry models have been unable to simultaneously simulate the measured daytime concentration of isoprene and that of its principal oxidant, hydroxyl (OH). One reason for this model-measurement discrepancy may be incomplete mixing of isoprene within the convective boundary layer, leading to patchiness or segregation in isoprene and OH mixing ratios and average concentrations that appear to be incompatible with each other. One way of capturing this effect in models of atmospheric chemistry is to use a reduced effective rate constant for their reaction. Recent studies comparing atmospheric chemistry global/box models with field measurements have suggested that this effective rate reduction may be as large as 50%; which is at the upper limit of that calculated using large eddy simulation models. To date there has only been one field campaign worldwide that has reported co-located measurements of isoprene and OH at the necessary temporal resolution to calculate the segregation of these compounds. However many campaigns have recorded sufficiently high resolution isoprene measurements to capture the small-scale fluctuations in its concentration. We use a box model of atmospheric chemistry, constrained by the spectrum of isoprene concentrations measured, to estimate segregation intensity of isoprene and OH from high-frequency isoprene time series. The method successfully reproduces the only directly observed segregation. The effective rate constant reduction for the reaction of isoprene and OH over a South-East Asian rainforest is calculated to be typically <15%. This estimate is not sensitive to heterogeneities in NO at this remote site, unless they are correlated with those of isoprene, or to OH-recycling schemes in the isoprene oxidation mechanism, unless the recycling happens in the first reaction step. Segregation alone is therefore unlikely to be the sole cause of model-measurement discrepancies for isoprene and OH above a rainforest.
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The statistical characteristics of mid-low latitude ionospheric E-region field-aligned irregularities (FAI) observed with the Kunming very high-frequency (VHF) radar are presented. First, the observational results show that the irregularities appeared mainly in periods before noon and near night, with the nighttime echoes being more intense and covering a greater height extent than that during the daytime. Second, we observed the existence of two well-defined types of echoes in the nighttime: the lower E-region echoes (115-130km) and upper E-region echoes (130-150km). Moreover, there are differences in FAI's motion characteristics at different range in the daytime and nighttime. Without in-field measurements, it is difficult to verify what physical mechanisms may explain the formation of the irregularities, which we will combine other facilities to analyze it in the future.
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The VOCs emissions from plants are mainly isoprene and monoterpenes, which account for 2/3 of the total emissions from biosphere. 23 kinds of typical plants in Beijing area were screened to estimate the emission rates of isoprene and monoterpenes by adopting a bag-enclosure sampling method followed by a GC-FID analysis. It was found that such deciduous trees as Sophora japnica and Salix babyloniaca etc. were mainly emitting isoprene and coniferous trees as Pinus tabulaetormis mainly released monoterpenes. The study also showed that the emission of isoprene were affected by both temperature and Photosynthetic Active Radiation (PAR), while monoterpene emissions were mainly temperature-dependent.
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Volatile organic compound
Monoterpene
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Gas-phase organic acids are ubiquitous throughout the atmosphere and are tracers for volatile organic compound oxidation, although their abundance and sources are poorly characterized. Several studies have pointed to the oxidation of isoprene and monoterpenes as major sources of formic and acetic acids. Here, we quantify >100 gas-phase organic acids produced from isoprene and α-pinene oxidation in a series of laboratory chamber experiments. Overall, gas-phase organic acids constitute 1–28% of the initial organic carbon reacted in the experiments. Isoprene is a precursor for detected organic acids in amounts at least 2–3× greater than α-pinene from OH oxidation. We compare laboratory observations with two summertime field sites—one dominated by isoprene emissions (Southern Oxidant and Aerosol Study—SOAS) and one by monoterpene emissions (Seasonal Particles in Forests Flux studY—SPiFFY). Daytime organic acid mixing ratios were 4× higher at SOAS than SPiFFY, likely because of the substantial isoprene OH oxidation. In contrast to SOAS, factor analysis reveals separate daytime and nighttime organic acid sources at SPiFFY not obviously originating from photochemical oxidation. When available, isoprene is likely a dominant precursor for gas-phase organic acids.
Isoprene
Volatile organic compound
Monoterpene
Organic acid
Pinene
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Isoprene
Atmospheric chemistry
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Abstract. Biogenic volatile organic compounds (BVOCs) such as isoprene constitute a large proportion of the global atmospheric oxidant sink. Their reactions in the atmosphere contribute to processes such as ozone production and secondary organic aerosol formation. However, over the tropical rainforest, where 50 % of the global emissions of BVOCs are believed to occur, atmospheric chemistry models have been unable to simulate concurrently the measured daytime concentration of isoprene and that of its principal oxidant, hydroxyl (OH). One reason for this model-measurement discrepancy may be incomplete mixing of isoprene within the convective boundary layer, leading to patchiness or segregation in isoprene and OH mixing ratios and average concentrations that appear to be incompatible with each other. One way of capturing this effect in models of atmospheric chemistry is to use a reduced effective rate constant for their reaction. Recent studies comparing atmospheric chemistry global/box models with field measurements have suggested that this effective rate reduction may be as large as 50 %; which is at the upper limit of that calculated using large eddy simulation models. To date there has only been one field campaign worldwide that has reported co-located measurements of isoprene and OH at the necessary temporal resolution to calculate the segregation of these compounds. However many campaigns have recorded sufficiently high resolution isoprene measurements to capture the small-scale fluctuations in its concentration. Assuming uniform distributions of other OH production and loss processes, we use a box model of atmospheric chemistry, constrained by the spectrum of isoprene concentrations measured, as a virtual instrument, to estimate the variability in OH at a point and hence, to estimate the segregation intensity of isoprene and OH from high-frequency isoprene time series. The method successfully reproduces the only directly observed segregation, using measurements made in a deciduous forest in Germany. The effective rate constant reduction for the reaction of isoprene and OH over a South-East Asian rainforest is calculated to be typically <15 %. Although there are many unconstrained uncertainties, the likely nature of those processes suggests that this value represents an upper limit. The estimate is not sensitive to heterogeneities in NO at this remote site, unless they are correlated with those of isoprene, or to OH-recycling schemes in the isoprene oxidation mechanism, unless the recycling happens in the first reaction step. Segregation alone is therefore unlikely to be the sole cause of model-measurement discrepancies for isoprene and OH above a rainforest.
Isoprene
Atmospheric chemistry
Chemical Transport Model
Box model
Mixing ratio
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Natural volatile organic compound (VOC) emissions were investigated at two forested sites in the southeastern United States. A variety of VOC compounds including methanol, 2‐methyl‐3‐buten‐2‐ol, 6‐methyl‐5‐hepten‐2‐one, isoprene and 15 monoterpenes were emitted from vegetation at these sites. Diurnal variations in VOC emissions were observed and related to light and temperature. Variations in isoprene emission from individual branches are well correlated with light intensity and leaf temperature while variations in monoterpene emissions can be explained by variations in leaf temperature alone. Isoprene emission rates for individual leaves tend to be about 75% higher than branch average emission rates due to shading on the lower leaves of a branch. Average daytime mixing ratios of 13.8 and 6.6 ppbv C isoprene and 5.0 and 4.5 ppbv C monoterpenes were observed at heights between 40 m and 1 km above ground level the two sites. Isoprene and monoterpenes account for 30% to 40% of the total carbon in the ambient non‐methane VOC quantified in the mixed layer at these sites and over 90% of the VOC reactivity with OH. Ambient mixing ratios were used to estimate isoprene and monoterpene fluxes by applying box model and mixed‐layer gradient techniques. Although the two techniques estimate fluxes averaged over different spatial scales, the average fluxes calculated by the two techniques agree within a factor of two. The ambient mixing ratios were used to evaluate a biogenic VOC emission model that uses field measurements of plant species composition, remotely sensed vegetation distributions, leaf level emission potentials determined from vegetation enclosures, and light and temperature dependent emission activity factors. Emissions estimated for a temperature of 30°C and above canopy photosynthetically active radiation flux of 1000 μmol m −2 s −1 are around 4 mg C m −2 h −1 of isoprene and 0.7 mg C m −2 h −1 of monoterpenes at the ROSE site in western Alabama and 3 mg C m −2 h −1 of isoprene and 0.5 mg C m −2 h −1 of monoterpenes at the SOS‐M site in eastern Georgia. Isoprene and monoterpene emissions based on land characteristics data and emission enclosure measurements are within a factor of two of estimates based on ambient measurements in most cases. This represents reasonable agreement due to the large uncertainties associated with these models and because the observed differences are at least partially due to differences in the size and location of the source region (“flux footprint”) associated with each flux estimate.
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Monoterpene
Volatile organic compound
Mixing ratio
Diurnal cycle
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The estimation of a biogenic volatile organic compound (BVOC, especially isoprene) and the influence of isoprene emissions on ozone concentrations in the Greater Busan Area (GBA) were carried out based on a numerical modeling approach during a high ozone episode. The BVOC emissions were estimated using a biogenic emission information system (BEIS v3.14) with vegetation data provided by the forest geographical information system (FGIS), land use data provided by the environmental geographical information system (EGIS), and meteorological data simulated by the MM5. Ozone simulation was performed by two sets of simulation scenarios: (1) without (CASE1) and (2) with isoprene emissions (CASE2). The isoprene emission (82 ton $day^{-1}$ ) in the GBA was estimated to be the most dominant BVOC followed by methanol (56) and carbon monoxide (28). Largest impacts of isoprene emissions on the ozone concentrations (CASE2-CASE1) were predicted to be about 4 ppb in inland locations where a high isoprene was emitted and to be about 2 ppb in the downwind and/or convergence regions of wind due to both the photochemical reaction of ozone precursors (e.g., high isoprene emissions) and meteorological conditions (e.g., local transport).
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