Abstract Space‐borne observations are used to characterize the fate of formaldehyde and glyoxal in wildfire plumes. Their distribution measured by the Tropospheric Monitoring Instrument reveals striking differences between the two compounds near intense fires. In typical situations, the glyoxal‐to‐formaldehyde ratio is highest near the fire (∼0.1) and decreases downwind of the source area due to the larger contribution of pyrogenic emissions to the glyoxal abundance and to the longer lifetime of formaldehyde. However, a pronounced glyoxal depletion is detected above high‐level clouds, not seen for formaldehyde, likely due to processing in pyrocumulonimbus clouds generated by the fires. This depletion suggests glyoxal retention upon droplet freezing and/or its outgassing in hydrated form in the upper troposphere. The absence of a sizable loss of formaldehyde during convection indicates that its hydration in liquid droplets and subsequent outgassing as methanediol represent at most a minor sink of formaldehyde.

Formic (HCOOH) and acetic acids (CH3COOH) are the most abundant carboxylic acids in the Earth's atmosphere and key compounds to aqueous-phase chemistry. Here we present the first distributions of CH3COOH retrieved from the 2007-2018 satellite observations of the nadir-looking infrared atmospheric sounding interferometer (IASI), using a neural network-based retrieval approach. A joint analysis with the IASI HCOOH product reveals that the two species exhibit similar distributions, seasonality, and atmospheric burden, pointing to major common sources. We show that their abundance is highly correlated to isoprene and monoterpenes emissions, as well as to biomass burning. Over Africa, evidence is provided that residual smoldering combustion might be a major driver of the HCOOH and CH3COOH seasonality. Earlier seasonal enhancement of HCOOH at Northern Hemisphere middle and high latitudes and late seasonal secondary peaks of CH3COOH in the tropics suggest that sources and production pathways specific to each species are also at play.

This study compares recent CO, NOx, NMVOC, SO2, BC, and OC anthropogenic emissions from several state-of-the-art top-down estimates to global and regional bottom-up inventories and projections from five Shared Socioeconomic Pathways (SSPs) in several regions. Results show that top-down emissions derived in several recent studies exhibit similar uncertainty as bottom-up inventories in some regions for certain species and even less in the case of Chinese CO emissions. In general, the largest discrepancies are found outside of regions such as the United States, Europe, and Japan where the most accurate and detailed information on emissions is available. In some regions such as China, which has recently undergone dynamical economic growth and changes in air quality regulations, the top-down estimates better capture recent emission trends than global bottom-up inventories. These results show the potential of top-down estimates to complement bottom-up inventories and to aide in the development of emission scenarios, particularly in regions where global inventories lack the necessary up-to-date and accurate information regarding regional activity data and emission factors such as Africa and India. Areas of future work aimed at quantifying and reducing uncertainty are also highlighted. A regional comparison of recent CO and NO(x)trends in the five SSPs indicate that SSP126, a strong pollution control scenario, best represents the trends from the top-down and regional bottom-up inventories in the United States, Europe, and China, while SSP460, a low-pollution control scenario, lies closest to actual trends in West Africa. This analysis can be useful for air quality forecasting and near-future pollution control/mitigation policy studies.

The understanding of biogenic volatile organic compound (BVOC) exchanges has become a key scientific issue because of their high reactivity and their impact in the atmosphere. However, so far, few studies have focused on BVOCs exchanged by agricultural species, and in particular by winter wheat, despite this species being the leading worldwide crop in terms of harvested area. This study for the first time investigated BVOC exchanges from winter wheat during most developmental stages of the plant. Fluxes were measured in Belgium at the ecosystem-scale using the disjunct eddy covariance by mass scanning technique, and a proton-transfer-reaction mass spectrometer for BVOC ambient mixing ratio measurements. As is usually observed for crops and grasses, the winter wheat field emitted mainly methanol, although bi-directional exchanges were observed. The second most exchanged compound was acetic acid which was captured during the entire growing season. Bi-directional exchanges of acetaldehyde and acetone were also reported. Terpene exchanges were 22 times smaller than oxygenated VOC (OVOC) exchanges. For all compounds, the exchanges were the most pronounced at the end of the growing season, i.e., under warm, dry and sunny conditions. Senescence-induced emissions were furthermore observed for methanol and acetaldehyde. For all investigated OVOCs, the exchanges very likely originated from both the soil and the plants. Despite their mixed origin, the MEGAN (Model of Emissions of Gases and Aerosols from Nature) v2.1 up-scaling model could adequately reproduce the methanol, acetaldehyde and acetone exchanges measured at this site during the mature and senescence phases of the plant, when the standard emission factor and the leaf age factor were adapted based on the measurements. In contrast, the model failed to reproduce the measured acetic acid exchanges. When the standard emission factor values currently assigned in MEGAN were applied, however, the exchanges were largely over-estimated for all compounds.

As one of the most abundant oxygenated volatile organic compounds in the atmosphere, acetone (CH3C[O]CH3) influences atmospheric oxidants levels and ozone formation. Here we report the first unambiguous identification of acetone from the nadir‐viewing satellite sounder Infrared Atmospheric Sounding Interferometer (IASI). Via a neural network‐based retrieval approach that was previously applied to the retrieval of other weak absorbers, we obtain daily global acetone retrievals. A first intercomparison with independent measurements is conducted. As the retrieval method is computationally fast, it allowed the full reprocessing of the 2007–2018 IASI time series. Analysis of the retrieved global product and its seasonality suggests that emissions of acetone and precursors from the terrestrial biosphere at Northern Hemisphere middle and high latitudes are the main contributors to the atmospheric acetone abundance, more than year‐round oxidation of anthropogenic isoalkanes. Remarkably, biomass burning does not appear to be a strong global source of acetone.

Retrieving concentrations of minor atmospheric trace gases from satellite observations is challenging due to their weak spectral signature. Here we present a new version of the ANNI (Artificial Neural Network for Infrared Atmospheric Sounding Interferometer, IASI) retrieval framework, which relies on a hyperspectral range index (HRI) for the quantification of the gas spectral signature and on an artificial feedforward neural network to convert the HRI into a gas total column. We detail the different steps of the retrieval method, especially where they differ from previous work, and apply the retrieval to three important volatile organic compounds: methanol (CH 3 OH), formic acid (HCOOH), and peroxyacetyl nitrate (PAN). The comparison of the retrieved columns with those from an optimal estimation inversion retrieval shows an overall excellent agreement: differences occur mainly when the sensitivity to the target gas is low and are consistent with the conceptual differences between the two approaches. We present retrieval examples over selected regions, comparison with previously developed products, and the global seasonal distributions including the first global distributions of PAN on a daily basis. The ANNI retrieval has been carried out on the whole time series of IASI observations (2007–2018), so that currently over 10 years of twice‐daily global CH 3 OH, HCOOH, and PAN total column distributions have been produced. This unique data set opens avenues for tackling important questions related to sources, transport, and transformation of volatile organic compounds in the global atmosphere.

Abstract A major feedback between climate and atmospheric chemistry lies in the meteorological dependence of the emissions of biogenic volatile organic compounds (BVOCs), precursors of important climate forcers, aerosols, and ozone. Whereas the short‐term response of BVOC emissions to meteorological drivers is fairly well simulated by current emission models, it is yet unclear whether models can faithfully predict their response to climate change, given the scarcity of long observation records of BVOC fluxes. Here we take advantage of the high yield of formaldehyde (HCHO) in the oxidation of VOCs and use a long‐term spaceborne record of HCHO observations in combination with model simulations to show that (i) HCHO interannual variability is primarily driven by climate through its impacts on photochemistry, vegetation fire occurrence, and above all, biogenic emissions and (ii) the HCHO record validates the interannual variability of biogenic emissions calculated by the state‐of‐the‐art Model of Emissions of Gases and Aerosols from Nature (MEGAN) emission model in vegetated regions.

As an ubiquitous product of the oxidation of many volatile organic compounds (VOCs), formaldehyde (HCHO) plays a key role as a short-lived and reactive intermediate in the atmospheric photo-oxidation pathways leading to the formation of tropospheric ozone and secondary organic aerosols. In this study, HCHO profiles have been successfully retrieved from ground-based Fourier transform infrared (FTIR) solar spectra and UV-visible Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) scans recorded during the July 2010–December 2012 time period at the Jungfraujoch station (Swiss Alps, 46.5° N, 8.0° E, 3580 m a.s.l.). Analysis of the retrieved products has revealed different vertical sensitivity between both remote sensing techniques. Furthermore, HCHO amounts simulated by two state-of-the-art chemical transport models (CTMs), GEOS-Chem and IMAGES v2, have been compared to FTIR total columns and MAX-DOAS 3.6–8 km partial columns, accounting for the respective vertical resolution of each ground-based instrument. Using the CTM outputs as the intermediate, FTIR and MAX-DOAS retrievals have shown consistent seasonal modulations of HCHO throughout the investigated period, characterized by summertime maximum and wintertime minimum. Such comparisons have also highlighted that FTIR and MAX-DOAS provide complementary products for the HCHO retrieval above the Jungfraujoch station. Finally, tests have revealed that the updated IR parameters from the HITRAN 2012 database have a cumulative effect and significantly decrease the retrieved HCHO columns with respect to the use of the HITRAN 2008 compilation.

Abstract. This paper evaluates the current status of global modeling of the organic aerosol (OA) in the troposphere and analyzes the differences between models as well as between models and observations. Thirty-one global chemistry transport models (CTMs) and general circulation models (GCMs) have participated in this intercomparison, in the framework of AeroCom phase II. The simulation of OA varies greatly between models in terms of the magnitude of primary emissions, secondary OA (SOA) formation, the number of OA species used (2 to 62), the complexity of OA parameterizations (gas-particle partitioning, chemical aging, multiphase chemistry, aerosol microphysics), and the OA physical, chemical and optical properties. The diversity of the global OA simulation results has increased since earlier AeroCom experiments, mainly due to the increasing complexity of the SOA parameterization in models, and the implementation of new, highly uncertain, OA sources. Diversity of over one order of magnitude exists in the modeled vertical distribution of OA concentrations that deserves a dedicated future study. Furthermore, although the OA / OC ratio depends on OA sources and atmospheric processing, and is important for model evaluation against OA and OC observations, it is resolved only by a few global models. The median global primary OA (POA) source strength is 56 Tg a−1 (range 34–144 Tg a−1) and the median SOA source strength (natural and anthropogenic) is 19 Tg a−1 (range 13–121 Tg a−1). Among the models that take into account the semi-volatile SOA nature, the median source is calculated to be 51 Tg a−1 (range 16–121 Tg a−1), much larger than the median value of the models that calculate SOA in a more simplistic way (19 Tg a−1; range 13–20 Tg a−1, with one model at 37 Tg a−1). The median atmospheric burden of OA is 1.4 Tg (24 models in the range of 0.6–2.0 Tg and 4 between 2.0 and 3.8 Tg), with a median OA lifetime of 5.4 days (range 3.8–9.6 days). In models that reported both OA and sulfate burdens, the median value of the OA/sulfate burden ratio is calculated to be 0.77; 13 models calculate a ratio lower than 1, and 9 models higher than 1. For 26 models that reported OA deposition fluxes, the median wet removal is 70 Tg a−1 (range 28–209 Tg a−1), which is on average 85% of the total OA deposition. Fine aerosol organic carbon (OC) and OA observations from continuous monitoring networks and individual field campaigns have been used for model evaluation. At urban locations, the model–observation comparison indicates missing knowledge on anthropogenic OA sources, both strength and seasonality. The combined model–measurements analysis suggests the existence of increased OA levels during summer due to biogenic SOA formation over large areas of the USA that can be of the same order of magnitude as the POA, even at urban locations, and contribute to the measured urban seasonal pattern. Global models are able to simulate the high secondary character of OA observed in the atmosphere as a result of SOA formation and POA aging, although the amount of OA present in the atmosphere remains largely underestimated, with a mean normalized bias (MNB) equal to −0.62 (−0.51) based on the comparison against OC (OA) urban data of all models at the surface, −0.15 (+0.51) when compared with remote measurements, and −0.30 for marine locations with OC data. The mean temporal correlations across all stations are low when compared with OC (OA) measurements: 0.47 (0.52) for urban stations, 0.39 (0.37) for remote stations, and 0.25 for marine stations with OC data. The combination of high (negative) MNB and higher correlation at urban stations when compared with the low MNB and lower correlation at remote sites suggests that knowledge about the processes that govern aerosol processing, transport and removal, on top of their sources, is important at the remote stations. There is no clear change in model skill with increasing model complexity with regard to OC or OA mass concentration. However, the complexity is needed in models in order to distinguish between anthropogenic and natural OA as needed for climate mitigation, and to calculate the impact of OA on climate accurately.

Abstract. Triggered by recent developments from laboratory and field studies regarding major NO x sink pathways in the troposphere, this study evaluates the influence of chemical uncertainties in NO x sinks for global NO x distributions calculated by the IMAGESv2 chemistry-transport model, and quantifies their significance for top-down NO x emission estimates. Our study focuses on five key chemical parameters believed to be of primary importance, more specifically, the rate of the reaction of NO 2 with OH radicals, the newly identified HNO 3 -forming channel in the reaction of NO with HO 2 , the reactive uptake of N 2 O 5 and HO 2 by aerosols, and the regeneration of OH in the oxidation of isoprene. Sensitivity simulations are performed to estimate the impact of each source of uncertainty. The model calculations show that, although the NO 2 +OH reaction is the largest NO x sink globally accounting for ca. 60% of the total sink, the reactions contributing the most to the overall uncertainty are the formation of HNO 3 in NO+HO 2 , leading to NO x column changes exceeding a factor of two over tropical regions, and the uptake of HO 2 by aqueous aerosols, in particular over East and South Asia. Emission inversion experiments are carried out using model settings which either minimise (MINLOSS) or maximise (MAXLOSS) the total NO x sink, both constrained by one year of OMI NO 2 column data from the DOMINO v2 KNMI algorithm. The choice of the model setup is found to have a major impact on the top-down flux estimates, with 75% higher emissions for MAXLOSS compared to the MINLOSS inversion globally. Even larger departures are found for soil NO (factor of 2) and lightning (1.8). The global anthropogenic source is better constrained (factor of 1.57) than the natural sources, except over South Asia where the combined uncertainty primarily associated to the NO+HO 2 reaction in summer and HO 2 uptake by aerosol in winter lead to top-down emission differences exceeding a factor of 2. Evaluation of the emission optimisation is performed against independent satellite observations from the SCIAMACHY sensor, with airborne NO 2 measurements of the INTEX-A and INTEX-B campaigns, as well as with two new bottom-up inventories of anthropogenic emissions in Asia (REASv2) and China (MEIC). Neither the MINLOSS nor the MAXLOSS setup succeeds in providing the best possible match with all independent datasets. Whereas the minimum sink assumption leads to better agreement with aircraft NO 2 profile measurements, consistent with the results of a previous analysis (Henderson et al., 2012), the same assumption leads to unrealistic features in the inferred distribution of emissions over China. Clearly, although our study addresses an important issue which was largely overlooked in previous inversion exercises, and demonstrates the strong influence of NO x loss uncertainties on top-down emission fluxes, additional processes need to be considered which could also influence the inferred source.

Abstract. Methanol exchanges over a mixed temperate forest in the Belgian Ardennes were measured for more than one vegetation season using disjunct eddy-covariance by a mass scanning technique and Proton Transfer Reaction Mass Spectrometry (PTR-MS). Half-hourly methanol fluxes were measured in the range of −0.6 μg m −2 s −1 to 0.6 μg m −2 s −1 , and net daily methanol fluxes were generally negative in summer and autumn and positive in spring. On average, the negative fluxes dominated (i.e. the site behaved as a net sink), in contrast to what had been found in previous studies. An original model describing the adsorption/desorption of methanol in water films present in the forest ecosystem and the methanol degradation process was developed. Its calibration, based on field measurements, predicted a mean methanol degradation rate of −0.0074 μg m −2 s −1 and a half lifetime for methanol in water films of 57.4 h. Biogenic emissions dominated the exchange only in spring, with a standard emission factor of 0.76 μg m −2 s −1 . The great ability of the model to reproduce the long-term evolution, as well as the diurnal variation of the fluxes, suggests that the adsorption/desorption and degradation processes play an important role in the global methanol budget. This result underlines the need to conduct long-term measurements in order to accurately capture these processes and to better estimate methanol fluxes at the ecosystem scale.

We present a new dataset of formaldehyde vertical columns retrieved from observations of GOME-2 on board the EUMETSAT MetOp-A platform between 2007 and 2011. The new retrieval scheme, which has been optimised for GOME-2, includes a two-step fitting procedure that strongly reduces the impact of spectral interferences between H2CO and BrO, and a modified DOAS approach that better handles ozone absorption effects at moderately low sun elevations. Owing to these new features, the noise in the H2CO slant columns is reduced by up to 40% in comparison to baseline retrieval settings used operationally. Also, the previously reported underestimation of the H2CO columns in tropical and mid-latitude regions has been largely eliminated, improving the agreement with coincident SCIAMACHY observations. To compensate for the drift of the GOME-2 slit function and to mitigate the instrumental degradation effects on H2CO retrievals, an asymmetric Gaussian line-shape is fitted during the irradiance calibration. Additionally, external parameters used in the tropospheric air mass factor computation (surface reflectances, cloud parameters and a priori profile shapes of H2CO) have been updated using most recent databases. Similar updates were also applied to the historical datasets of GOME and SCIAMACHY, leading to the generation of a consistent multi-mission H2CO data record covering the time period from 1997 until 2011. Comparing the resulting time series of monthly averaged H2CO vertical columns in 12 large regions worldwide, the correlation coefficient between SCIAMACHY and GOME-2 columns is generally higher than 0.8 in the overlap period, and linear regression slopes differ by less than 10% from unity in most of the regions. In comparison to SCIAMACHY, the largely improved spatial sampling of GOME-2 allows for a better characterisation of formaldehyde distribution at the regional scale and/or at shorter timescales, leading to a better identification of the emission sources of non-methane volatile organic compounds.

A new parameter model for α-pinene secondary organic aerosol (SOA) is presented, based on simulations with the detailed model BOREAM (Biogenic hydrocarbon Oxidation and Related Aerosol formation Model). The parameterisation takes into account the influence of temperature, type of oxidant, NOx-regime, photochemical ageing and water uptake, and is suitable for use in global chemistry transport models. BOREAM is validated against recent photooxidation smog chamber experiments, for which it reproduces SOA yields to within a factor of 2 in most cases. In the simple chemical mechanism of the parameter model, oxidation of α-pinene generates peroxy radicals, which, upon reaction with NO or HO2, yield products corresponding to high or low-NOx conditions, respectively. The model parameters – i.e. the temperature-dependent stoichiometric coefficients and partitioning coefficients of 10 semi-volatile products – are obtained from simulations with BOREAM, including a prescribed diurnal cycle for the radiation, oxidant and emission levels, as well as a deposition sink for the particulate and gaseous products. The effects of photooxidative ageing are implicitly included in the parameterisation, since it is based on near-equilibrium SOA concentrations, obtained through simulations of a two-week period. In order to mimic the full BOREAM model results both during SOA build-up and when SOA has reached an equilibrium concentration, the revolatilisation of condensable products due to photochemical processes is taken into account through a fitted pseudo-photolysis reaction of the lumped semi-volatile products. Modelled SOA mass yields are about ten times higher in low-NOx than in high-NOx conditions, with yields of more than 50% in the low-NOx OH-initiated oxidation of α-pinene, considerably more than in previous parameterisations based on smog chamber experiments. Sensitivity calculations indicate that discrepancies between the full model and the parameterisation due to variations in assumed oxidant levels are limited, but that changes in the radiation levels can lead to larger deviations. Photolysis of species in the particulate phase is found to strongly reduce SOA yields in the full model. Simulations of ambient conditions at 17 different sites (using oxidant, radiation and meteorological data from a global chemistry-transport model) show that overall, the parameterisation displays only little bias (2%) compared with the full model, whereas averaged relative deviations amount to about 11%. Water uptake is parameterised using fitted activity coefficients, resulting in a good agreement with the full model.

Reunion Island (21° S, 55° E), situated in the Indian Ocean at about 800 km east of Madagascar, is appropriately located to monitor the outflow of biomass burning pollution from Southern Africa and Madagascar, in the case of short-lived compounds, and from other Southern Hemispheric landmasses such as South America, in the case of longer-lived species. Ground-based Fourier transform infrared (FTIR) solar absorption observations are sensitive to a large number of biomass burning products. We present in this work the FTIR retrieval strategies, suitable for very humid sites such as Reunion Island, for hydrogen cyanide (HCN), ethane (C2H6), acetylene (C2H2), methanol (CH3OH), and formic acid (HCOOH). We provide their total columns time-series obtained from the measurements during August–October 2004, May–October 2007, and May 2009–December 2010. We show that biomass burning explains a large part of the observed seasonal and interannual variability of the chemical species. The correlations between the daily mean total columns of each of the species and those of CO, also measured with our FTIR spectrometer at Reunion Island, are very good from August to November (R ≥ 0.86). This allows us to derive, for that period, the following enhancement ratios with respect to CO: 0.0047, 0.0078, 0.0020, 0.012, and 0.0046 for HCN, C2H6, C2H2, CH3OH, and HCOOH, respectively. The HCN ground-based data are compared to the chemical transport model GEOS-Chem, while the data for the other species are compared to the IMAGESv2 model. We show that using the HCN/CO ratio derived from our measurements (0.0047) in GEOS-Chem reduces the underestimation of the modeled HCN columns compared with the FTIR measurements. The comparisons between IMAGESv2 and the long-lived species C2H6 and C2H2 indicate that the biomass burning emissions used in the model (from the GFED3 inventory) are probably underestimated in the late September–October period for all years of measurements, and especially in 2004. The comparisons with the short-lived species, CH3OH and HCOOH, with lifetimes of around 5 days, suggest that the emission underestimation in late September–October 2004, occurs more specifically in the Southeastern Africa-Madagascar region. The very good correlation of CH3OH and HCOOH with CO suggests that, despite the dominance of the biogenic source of these compounds on the global scale, biomass burning is their major source at Reunion Island between August and November.

Multicomponent organic aerosol (OA) is likely to be liquid, or partially liquid. Hence, to describe the partitioning of these components, their liquid vapour pressure is desired. Functionalised acids (e.g. diacids) can be a significant part of OA. But often measurements are available only for solid state vapour pressure, which can differ by orders of magnitude from their liquid counterparts. To convert such a sublimation pressure to a subcooled liquid vapour pressure, fusion properties (two out of these three quantities: fusion enthalpy, fusion entropy, fusion temperature) are required. Unfortunately, experimental knowledge of fusion properties is sometimes missing in part or completely, hence an estimation method is required. Several fusion data estimation methods are tested here against experimental data of functionalised acids, and a simple estimation method is developed, specifically for this family of compounds, with a significantly smaller estimation error than the literature methods.

We present an evaluation of a nested high-resolution Goddard Earth Observing System (GEOS)-Chem chemistry transport model simulation of tropospheric chemistry over tropical South America. The model has been constrained with two isoprene emission inventories: (1) the canopy-scale Model of Emissions of Gases and Aerosols from Nature (MEGAN) and (2) a leaf-scale algorithm coupled to the Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS) dynamic vegetation model, and the model has been run using two different chemical mechanisms that contain alternative treatments of isoprene photo-oxidation. Large differences of up to 100 Tg C yr^(−1) exist between the isoprene emissions predicted by each inventory, with MEGAN emissions generally higher. Based on our simulations we estimate that tropical South America (30–85°W, 14°N–25°S) contributes about 15–35% of total global isoprene emissions. We have quantified the model sensitivity to changes in isoprene emissions, chemistry, boundary layer mixing, and soil NO_x emissions using ground-based and airborne observations. We find GEOS-Chem has difficulty reproducing several observed chemical species; typically hydroxyl concentrations are underestimated, whilst mixing ratios of isoprene and its oxidation products are overestimated. The magnitude of model formaldehyde (HCHO) columns are most sensitive to the choice of chemical mechanism and isoprene emission inventory. We find GEOS-Chem exhibits a significant positive bias (10–100%) when compared with HCHO columns from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and Ozone Monitoring Instrument (OMI) for the study year 2006. Simulations that use the more detailed chemical mechanism and/or lowest isoprene emissions provide the best agreement to the satellite data, since they result in lower-HCHO columns.

We measured the isoprene and monoterpene fluxes continuously above a mixed forest site at Vielsalm in the eastern part of Belgium, using the disjunct eddy covariance technique with proton transfer reaction-mass spectrometry. Simultaneously, we also measured the carbon dioxide fluxes in order to deduce the gross primary production. The measurements were conducted from July to September 2009.During the day, the seasonal evolution of the isoprene/monoterpene emissions was studied using a monthly temperature and light dependence function deduced from our results to standardize the fluxes. A seasonal decrease in the standard emission factors was observed, probably linked to acclimation or senescence. The standard emission factor for isoprene fluxes (30 degrees C, 1000 mu mol m(-2) s(-1)) fell from 0.91 +/- 0.01 to 0.56 +/- 0.02 pig m(-2) s(-1) and for monoterpene fluxes from 0.74 +/- 0.03 to 0.27 0.03 mu g m(-2) s(-1).During the night, a slight positive flux of monoterpenes was observed that seemed to be driven by air temperature. The standard emission factor (30 degrees C) for nighttime monoterpene fluxes was equal to 0.093 +/- 0.019 mu g m(-2) s(-1).Finally, we studied the seasonal evolution of the relationship between the gross primary production and the isoprene/monoterpenes fluxes. A linear relationship was observed, highlighting the strong link between carbon assimilation and isoprene/monoterpene emissions. (C) 2011 Elsevier Ltd. All rights reserved.

We applied and compared seven vapor pressure estimation methods to the condensable compounds generated in the oxidation of α-pinene, as described by the state-of-the-art mechanism of the BOREAM model Capouet et al., 2008. Several of these methods had to be extended in order to treat functional groups such as hydroperoxides and peroxy acyl nitrates. Large differences in the estimated vapor pressures are reported, which will inevitably lead to large differences in aerosol formation simulations. Cautioning remarks are given for some vapor pressure estimation methods.

Tropospheric glyoxal and formaldehyde columns retrieved from the SCIAMACHY satellite instrument in 2005 are used with the IMAGESv2 global chemistry-transport model and its adjoint in a two-compound inversion scheme designed to estimate the continental source of glyoxal. The formaldehyde observations provide an important constraint on the production of glyoxal from isoprene in the model, since the degradation of isoprene constitutes an important source of both glyoxal and formaldehyde. Current modelling studies underestimate largely the observed glyoxal satellite columns, pointing to the existence of an additional land glyoxal source of biogenic origin. We include an extra glyoxal source in the model and we explore its possible distribution and magnitude through two inversion experiments. In the first case, the additional source is represented as a direct glyoxal emission, and in the second, as a secondary formation through the oxidation of an unspecified glyoxal precursor. Besides this extra source, the inversion scheme optimizes the primary glyoxal and formaldehyde emissions, as well as their secondary production from other identified non-methane volatile organic precursors of anthropogenic, pyrogenic and biogenic origin.In the first inversion experiment, the additional direct source, estimated at 36 Tg/yr, represents 38% of the global continental source, whereas the contribution of isoprene is equally important (30%), the remainder being accounted for by anthropogenic (20%) and pyrogenic fluxes. The inversion succeeds in reducing the underestimation of the glyoxal columns by the model, but it leads to a severe overestimation of glyoxal surface concentrations in comparison with in situ measurements. In the second scenario, the inferred total global continental glyoxal source is estimated at 108 Tg/yr, almost two times higher than the global a priori source. The extra secondary source is the largest contribution to the global glyoxal budget (50%), followed by the production from isoprene (26%) and from anthropogenic NMVOC precursors (14%). A better performance is achieved in this case, as the updated emissions allow for a satisfactory agreement of the model with both satellite and in situ glyoxal observations.

Formaldehyde columns retrieved from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography/Chemistry (SCIAMACHY) instrument onboard ENVISAT satellite through 2003 to 2006 are used as top-down constraints to derive updated global biogenic and biomass burning flux estimates for the non-methane volatile organic compounds (NMVOCs) precursors of formaldehyde. Our interest is centered over regions experiencing strong emissions, and hence exhibiting a high signal-to-noise ratio and lower measurement uncertainties. The formaldehyde dataset used in this study has been recently made available to the community and complements the long record of formaldehyde measurements from the Global Ozone Monitoring Experiment (GOME). We use the IMAGESv2 global chemistry-transport model driven by the Global Fire Emissions Database (GFED) version 1 or 2 for biomass burning, and from the newly developed MEGAN-ECMWF isoprene emission database. The adjoint of the model is implemented in a grid-based framework within which emission fluxes are derived at the model resolution, together with a differentiation of the sources in a grid cell. Two inversion studies are conducted using either the GFEDv1 or GFEDv2 as a priori for the pyrogenic fluxes. Although on the global scale the inferred emissions from the two categories exhibit only weak deviations from the corresponding a priori estimates, the regional updates often present large departures from their a priori values. The posterior isoprene emissions over North America, amounting to about 34 Tg C/yr, are estimated to be on average by 25% lower than the a priori over 2003–2006, whereas a strong increase (55%) is deduced over the south African continent, the optimized emission being estimated at 57 Tg C/yr. Over Indonesia the biogenic emissions appear to be overestimated by 20–30%, whereas over Indochina and the Amazon basin during the wet season the a priori inventory captures both the seasonality and the magnitude of the observed columns. Although neither biomass burning inventory seems to be consistent with the data over all regions, pyrogenic estimates inferred from the two inversions are reasonably similar, despite their a priori deviations. A number of sensitivity experiments are conducted in order to assess the impact of uncertainties related to the inversion setup and the chemical mechanism. Whereas changes in the background error covariance matrix have only a limited impact on the posterior fluxes, the use of an alternative isoprene mechanism characterized by lower HCHO yields (the GEOS-Chem mechanism) increases the posterior isoprene source estimate by 11% over northern America, and by up to 40% in tropical regions.