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This paper studies the seasonal variation of surface and column CO at three different sites (Paris, Jungfraujoch and Wollongong), with an emphasis on establishing a link between the CO vertical distribution and the nature of CO emission sources. We find the first evidence of a time lag between surface and free tropospheric CO seasonal variations in the Northern Hemisphere. The CO seasonal variability obtained from the total columns and free tropospheric partial columns shows a maximum around March-April and a minimum around September-October in the Northern Hemisphere (Paris and Jungfraujoch). In the Southern Hemisphere (Wollongong) this seasonal variability is shifted by about 6 months. Satellite observations by the IASI-MetOp (Infrared Atmospheric Sounding Interferometer) and MOPITT (Measurements Of Pollution In The Troposphere) instruments confirm this seasonality. Ground-based FTIR (Fourier transform infrared) measurements provide useful complementary information due to good sensitivity in the boundary layer. In situ surface measurements of CO volume mixing ratios at the Paris and Jungfraujoch sites reveal a time lag of the near-surface seasonal variability of about 2 months with respect to the total column variability at the same sites. The chemical transport model GEOS-Chem (Goddard Earth Observing System chemical transport model) is employed to interpret our observations. GEOS-Chem sensitivity runs identify the emission sources influencing the seasonal variation of CO. At both Paris and Jungfraujoch, the surface seasonality is mainly driven by anthropogenic emissions, while the total column seasonality is also controlled by air masses transported from distant sources. At Wollongong, where the CO seasonality is mainly affected by biomass burning, no time shift is observed between surface measurements and total column data.

Formic acid (HCOOH) is one of the most abundant volatile organic compounds in the atmosphere. It is a major contributor to rain acidity in remote areas. There are, however, large uncertainties on the sources and sinks of HCOOH and therefore HCOOH is misrepresented by global chemistry-transport models. This work presents global distributions from 2008 to 2014 as derived from the measurements of the Infrared Atmospheric Sounding Interferometer (IASI), based on conversion factors between brightness temperature differences and representative retrieved total columns over seven regions: Northern Africa, southern Africa, Amazonia, Atlantic, Australia, Pacific, and Russia. The dependence of the measured HCOOH signal on the thermal contrast is taken into account in the conversion method. This conversion presents errors lower than 20 % for total columns ranging between 0.5 and 1 x 1016 molec cm−2 but reaches higher values, up to 78 %, for columns that are lower than 0.3 x 1016 molec cm−2. Signatures from biomass burning events are highlighted, such as in the Southern Hemisphere and in Russia, as well as biogenic emission sources, e.g., over the eastern USA. A comparison between 2008 and 2014 with ground-based Fourier transform infrared spectroscopy (FTIR) measurements obtained at four locations (Maido and Saint-Denis at La Réunion, Jungfraujoch, and Wollongong) is shown. Although IASI columns are found to correlate well with FTIR data, a large bias (> 100 %) is found over the two sites at La Réunion. A better agreement is found at Wollongong with a negligible bias. The comparison also highlights the difficulty of retrieving total columns from IASI measurements over mountainous regions such as Jungfraujoch. A comparison of the retrieved columns with the global chemistry-transport model IMAGESv2 is also presented, showing good representation of the seasonal and interannual cycles over America, Australia, Asia, and Siberia. A global model underestimation of the distribution and

Marine nitrogen fixation is co-limited by the supply of iron (Fe) and phosphorus in large regions of the global ocean. The deposition of soluble aerosol Fe can initiate nitrogen fixation and trigger toxic algal blooms in nitrate-poor tropical waters. We present dry season soluble Fe data from the Savannah Fires in the Early Dry Season (SAFIRED) campaign in northern Australia that reflects coincident dust and biomass burning sources of soluble aerosol Fe. The mean soluble and total aerosol Fe concentrations were 40 and 500 ng m-3 respectively. Our results show that while biomass burning species may not be a direct source of soluble Fe, biomass burning may substantially enhance the solubility of mineral dust. We observed fractional Fe solubility up to 12% in mixed aerosols. Thus, Fe in dust may be more soluble in the tropics compared to higher latitudes due to higher concentrations of biomass-burning-derived reactive organic species in the atmosphere. In addition, biomass-burning-derived particles can act as a surface for aerosol Fe to bind during atmospheric transport and subsequently be released to the ocean upon deposition. As the aerosol loading is dominated by biomass burning emissions over the tropical waters in the dry season, additions of biomass-burning-derived soluble Fe could have harmful consequences for initiating nitrogen-fixing toxic algal blooms. Future research is required to quantify biomass-burning-derived particle sources of soluble Fe over tropical waters.

We investigate the impact of biogenic emissions on carbon monoxide (CO) and formaldehyde (HCHO) in the Southern Hemisphere (SH), with simulations using two different biogenic emission inventories for isoprene and monoterpenes. Results from four atmospheric chemistry models are compared to continuous long-term ground-based CO and HCHO column measurements at the SH Network for the Detection of Atmospheric Composition Change (NDACC) sites, the satellite measurement of tropospheric CO columns from the Measurement of Pollution in the Troposphere (MOPITT), and in situ surface CO measurements from across the SH, representing a subset of the National Oceanic and Atmospheric Administration's Global Monitoring Division (NOAA GMD) network. Simulated mean model CO using the Model of Emissions of Gases and Aerosols from Nature (v2.1) computed in the frame work of the Land Community Model (CLM-MEGANv2.1) inventory is in better agreement with both column and surface observations than simulations adopting the emission inventory generated from the LPJ-GUESS dynamical vegetation model framework, which markedly underestimate measured column and surface CO at most sites. Differences in biogenic emissions cause large differences in CO in the source regions which propagate to the remote SH. Significant inter-model differences exist in modelled column and surface CO, and secondary production of CO dominates these inter-model differences, due mainly to differences in the models' oxidation schemes for volatile organic compounds, predominantly isoprene oxidation. While biogenic emissions are a significant factor in modelling SH CO, inter-model differences pose an additional challenge to constrain these emissions. Corresponding comparisons of HCHO columns at two SH mid-latitude sites reveal that all models significantly underestimate the observed values by approximately a factor of 2. There is a much smaller impact on HCHO of the significantly different biogenic emissions in remote regions, c

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We present global distributions of C2H2 and hydrogen cyanide (HCN) total columns derived from the Infrared Atmospheric Sounding Interferometer (IASI) for the years 2008-2010. These distributions are obtained with a fast method allowing to retrieve C2H2 abundance globally with a 5 % precision and HCN abundance in the tropical (subtropical) belt with a 10 % (25 %) precision. IASI data are compared for validation purposes with ground-based Fourier transform infrared (FTIR) spectrometer measurements at four selected stations. We show that there is an overall agreement between the ground-based and space measurements with correlation coefficients for daily mean measurements ranging from 0.28 to 0.81, depending on the site. Global C2H2 and subtropical HCN abundances retrieved from IASI spectra show the expected seasonality linked to variations in the anthropogenic emissions and seasonal biomass burning activity, as well as exceptional events, and are in good agreement with previous spaceborne studies. Total columns simulated by the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4) are compared to the ground-based FTIR measurements at the four selected stations. The model is able to capture the seasonality in the two species in most of the cases, with correlation coefficients for daily mean measurements ranging from 0.50 to 0.86, depending on the site. IASI measurements are also compared to the distributions from MOZART-4. Seasonal cycles observed from satellite data are reasonably well reproduced by the model with correlation coefficients ranging from −0.31 to 0.93 for C2H2 daily means, and from 0.09 to 0.86 for HCN daily means, depending on the considered region. However, the anthropogenic (biomass burning) emissions used in the model seem to be overestimated (underestimated), and a negative global mean bias of 1 % (16 %) of the model relative to the satellite observations was found for C2H2 (HCN).

We investigate Arctic tropospheric composition using ground-based Fourier transform infrared (FTIR) solar absorption spectra, recorded at the Polar Environment Atmospheric Research Laboratory (PEARL, Eureka, Nunavut, Canada, 80°05' N, 86°42' W) and at Thule (Greenland, 76°53' N, −68°74' W) from 2008 to 2012. The target species, carbon monoxide (CO), hydrogen cyanide (HCN), ethane (C2H6), acetylene (C2H2), formic acid (HCOOH), and formaldehyde (H2CO) are emitted by biomass burning and can be transported from mid-latitudes to the Arctic. By detecting simultaneous enhancements of three biomass burning tracers (HCN, CO, and C2H6), ten and eight fire events are identified at Eureka and Thule, respectively, within the 5-year FTIR time series. Analyses of Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model back-trajectories coupled with Moderate Resolution Imaging Spectroradiometer (MODIS) fire hotspot data, Stochastic Time-Inverted Lagrangian Transport (STILT) model footprints, and Ozone Monitoring Instrument (OMI) UV aerosol index maps, are used to attribute burning source regions and travel time durations of the plumes. By taking into account the effect of aging of the smoke plumes, measured FTIR enhancement ratios were corrected to obtain emission ratios and equivalent emission factors. The means of emission factors for extratropical forest estimated with the two FTIR data sets are 0.40 ± 0.21 g kg−1 for HCN, 1.24 ± 0.71 g kg−1 for C2H6, 0.34 ± 0.21 g kg−1 for C2H2, and 2.92 ± 1.30 g kg−1 for HCOOH. The emission factor for CH3OH estimated at Eureka is 3.44 ± 1.68 g kg−1. To improve our knowledge concerning the dynamical and chemical processes associated with Arctic pollution from fires, the two sets of FTIR measurements were compared to the Model for OZone And Related chemical Tracers, version 4 (MOZART-4). Seasonal cycles and day-to-day variabilities were compared to assess the ability of the model to reproduce emissions from fires and their transp

Biomass burning releases trace gases and aerosol particles that significantly affect the composition and chemistry of the atmosphere. Australia contributes approximately 8% of gross global carbon emissions from biomass burning, yet there are few previous measurements of emissions from Australian forest fires available in the literature. This paper describes the results of field measurements of trace gases emitted during hazard reduction burns in Australian temperate forests using open-path Fourier transform infrared spectroscopy. In a companion paper, similar techniques are used to characterise the emissions from hazard reduction burns in the savanna regions of the Northern Territory. Details of the experimental methods are explained, including both the measurement set-up and the analysis techniques employed. The advantages and disadvantages of different ways to estimate whole-fire emission factors are discussed and a measurement uncertainty budget is developed. Emission factors for Australian temperate forest fires are measured locally for the first time for many trace gases. Where ecosystem-relevant data are required, we recommend the following emission factors for Australian temperate forest fires (in grams of gas emitted per kilogram of dry fuel burned) which are our mean measured values: 1620 ± 160 g kg−1 of carbon dioxide; 120 ± 20 g kg−1 of carbon monoxide; 3.6 ± 1.1 g kg−1 of methane; 1.3 ± 0.3 g kg−1 of ethylene; 1.7 ± 0.4 g kg−1 of formaldehyde; 2.4 ± 1.2 g kg−1 of methanol; 3.8 ± 1.3 g kg−1 of acetic acid; 0.4 ± 0.2 g kg−1 of formic acid; 1.6 ± 0.6 g kg−1 of ammonia; 0.15 ± 0.09 g kg−1 of nitrous oxide and 0.5 ± 0.2 g kg−1 of ethane.

Savanna fires contribute approximately 40-50% of total global annual biomass burning carbon emissions. Recent comparisons of emission factors from different savanna regions have highlighted the need for a regional approach to emission factor development, and better assessment of the drivers of the temporal and spatial variation in emission factors. This paper describes the results of open-path Fourier transform infrared (OP-FTIR) spectroscopic field measurements at 21 fires occurring in the tropical savannas of the Northern~Territory, Australia, within different vegetation assemblages and at different stages of the dry season. Spectra of infrared light passing through a long (22-70 m) open-path through ground-level smoke released from these fires were collected using an infrared lamp and a field-portable FTIR system. The IR spectra were used to retrieve the mole fractions of 14 different gases present within the smoke, and these measurements used to calculate the emission ratios and emission factors of the various gases emitted by the burning. Only a handful of previous emission factor measures are available specifically for the tropical savannas of Australia and here we present the first reported emission factors for methanol, acetic acid, and formic acid for this biome. Given the relatively large sample size, it was possible to study the potential causes of the within-biome variation of the derived emission factors. We find that the emission factors vary substantially between different savanna vegetation assemblages; with a majority of this variation being mirrored by variations in the modified combustion efficiency (MCE) of different vegetation classes. We conclude that a significant majority of the variation in the emission factor for trace gases can be explained by MCE, irrespective of vegetation class, as illustrated by variations in the calculated methane emission factor for different vegetation classes using data sub-set by different combustion efficiencies.

Time series of total column abundances of hydrogen chloride (HCl), chlorine nitrate (ClONO2), and hydrogen fluoride (HF) were determined from ground-based Fourier transform infrared (FTIR) spectra recorded at 17 sites belonging to the Network for the Detection of Atmospheric Composition Change (NDACC) and located between 80.05° N and 77.82° S. By providing such a near-global overview on ground-based measurements of the two major stratospheric chlorine reservoir species, HCl and ClONO2, the present study is able to confirm the decrease of the atmospheric inorganic chlorine abundance during the last few years. This decrease is expected following the 1987 Montreal Protocol and its amendments and adjustments, where restrictions and a subsequent phase-out of the prominent anthropogenic chlorine source gases (solvents, chlorofluorocarbons) were agreed upon to enable a stabilisation and recovery of the stratospheric ozone layer. The atmospheric fluorine content is expected to be influenced by the Montreal Protocol, too, because most of the banned anthropogenic gases also represent important fluorine sources. But many of the substitutes to the banned gases also contain fluorine so that the HF total column abundance is expected to have continued to increase during the last few years. The measurements are compared with calculations from five different models: the two-dimensional Bremen model, the two chemistry-transport models KASIMA and SLIMCAT, and the two chemistry-climate models EMAC and SOCOL. Thereby, the ability of the models to reproduce the absolute total column amounts, the seasonal cycles, and the temporal evolution found in the FTIR measurements is investigated and inter-compared. This is especially interesting because the models have different architectures. The overall agreement between the measurements and models for the total column abundances and the seasonal cycles is good. Linear trends of HCl, ClONO2, and HF are calculated from both measurement and model t

Carbon monoxide (CO) is retrieved daily and globally from space-borne IASI radiance spectra using the Fast Optimal Retrievals on Layers for IASI (FORLI) software developed at the Universit´e Libre de Bruxelles (ULB). The IASI CO total column product for 2008 from the most recent FORLI retrieval version (20100815) is evaluated using correlative CO profile products retrieved from groundbased solar absorption Fourier transform infrared (FTIR) observations at the following FTIR spectrometer sites from the Network for the Detection of Atmospheric Composition Change (NDACC): Ny-A° lesund, Kiruna, Bremen, Jungfraujoch, Iza˜na and Wollongong. In order to have good statistics for the comparisons, we included all IASI data from the same day, within a 100 km radius around the ground-based stations. The individual ground-based data were adjusted to the lowest altitude of the co-located IASI CO profiles. To account for the different vertical resolutions and sensitivities of the ground-based and satellite measurements, the averaging kernels associated with the various retrieved products have been used to properly smooth coincident data products. It has been found that the IASI CO total column products compare well on average with the co-located ground-based FTIR total columns at the selected NDACC sites and that there is no significant bias for the mean values at all stations.

We present a comparison of techniques for estimating atmospheric emissions from fires using Australia's 2009 "Black Saturday" wildfires as a case study. Most of the fires started on Saturday the 7th of February 2009 (a date now known as "Black Saturday") and then spread rapidly, fanned by gale force winds, creating several firestorms and killing 173 people. The fires continued into early March, when rain and cooler conditions allowed the fires to be extinguished. In this study, we compare two new techniques (and one more established method) to estimate the total emissions of a number of atmospheric trace gases from these fires. One of the new techniques is a "bottom-up" technique that combines existing inventories of fuel loads, combustion efficiencies and emission factors with an estimate of burned area derived from MODIS rapid response daily fire counts. The other new method is a "top-down" approach using MODIS aerosol optical depth as a proxy for total amounts of trace gases emitted by the fires. There are significant differences between the estimates of emissions from these fires using the different methods, highlighting the uncertainties associated with fire emission estimates. These differences are discussed along with their likely causes and used as a vehicle to explore the merits of the different methods, and further constrain fire emissions in the future.

We use Fourier transfonn infrared ground-based measurements and satellite and model data to assess long-range correlations in tropospheric carbon monoxide. We fmd that CO columns measured in New Zealand correlate well with those measured in Antarctica, if a transport-related lag is taken into account. The model suggests that this long-range correlation is part of a mode of anomalous CO comprising almost the whole southern extratropics, which is linked to biomass burning in the southern continents. No such mode is modeled for the Northern Hemisphere. The area of long-range correlations maximizes for the southern subtropical Pacific, which is identified as an advantageous location for a hypothetical new measurement station. The satellite data (produced by the Measurements of Pollution in the Troposphere (MOPlTT) instrument) partially confinn these fmdings but with generally reduced correlations. In particular, the satellite data suggest no long-range correlation at high latitudes. This is partially explained in terms of retrieval limitations and partially reflects a model deficiency.

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Formic acid contributes significantly to acid rain in remote environments. Direct sources of formic acid include human activities, biomass burning and plant leaves. Aside from these direct sources, sunlight-induced oxidation of non-methane hydrocarbons (largely of biogenic origin) is probably the largest source. However, model simulations substantially underpredict atmospheric formic acid levels, indicating that not all sources have been included in the models. Here, we use satellite measurements of formic acid concentrations to constrain model simulations of the global formic acid budget. According to our simulations, 100- 120Tg of formic acid is produced annually, which is two to three times more than that estimated from known sources. We show that 90% of the formic acid produced is biogenic in origin, and largely sourced from tropical and boreal forests. We suggest that terpenoids- volatile organic compounds released by plants- are the predominant precursors. Model comparisons with independent observations of formic acid strengthen our conclusions, and provide indirect validation for the satellite measurements. Finally, we show that the larger formic acid emissions have a substantial impact on rainwater acidity, especially over boreal forests in the summer, where formic acid reduces pH by 0.25- 0.5., SCOPUS: ar.j, SCOPUS: ar.j, info:eu-repo/semantics/published

The ‘Black Saturday’ fires were a series of devastating forest fires that burned across Victoria, Australia, during February and March of 2009. In this study we have used satellite data made publically available by NASA from the Ozone Monitoring Instrument (OMI) and the Atmospheric InfraRed Sounder (AIRS) to track the smoke plume from the Black Saturday firestorm and explore the chemical aging of the smoke plume in the first days after emission. We also determined emission ratios for formaldehyde and nitrogen dioxide within smoke from fires actively burning across Victoria between 7 and 17 February 2009. The mean emission ratios with respect to carbon monoxide derived for these two tropospheric ozone precursors are (0.016 ± 0.004 mol.mol−1) for formaldehyde and (0.005 ± 0.002 mol.mol−1) for nitrogen dioxide. The mean emission ratio for formaldehyde with respect to CO is in broad agreement with values previously quoted in the literature for temperate forest fires. However, to our knowledge there are no previous measurements of emission ratios for nitrogen dioxide from Australian temperate forest fires.

Formic acid contributes significantly to acid rain in remote environments1, 2. Direct sources of formic acid include human activities, biomass burning and plant leaves. Aside from these direct sources, sunlight-induced oxidation of non-methane hydrocarbons (largely of biogenic origin) is probably the largest source3, 4. However, model simulations substantially underpredict atmospheric formic acid levels5, 6, 7, indicating that not all sources have been included in the models. Here, we use satellite measurements of formic acid concentrations to constrain model simulations of the global formic acid budget. According to our simulations, 100–120 Tg of formic acid is produced annually, which is two to three times more than that estimated from known sources. We show that 90% of the formic acid produced is biogenic in origin, and largely sourced from tropical and boreal forests. We suggest that terpenoids—volatile organic compounds released by plants—are the predominant precursors. Model comparisons with independent observations of formic acid strengthen our conclusions, and provide indirect validation for the satellite measurements. Finally, we show that the larger formic acid emissions have a substantial impact on rainwater acidity, especially over boreal forests in the summer, where formic acid reduces pH by 0.25–0.5.

The changing composition of the earth’s atmosphere is a matter of intense scientific research as we strive to understand details of the physical and chemical mechanisms that control our climate. Fourier transform spectroscopy has been applied very successfully to the study of trace gases in the atmosphere by examining terrestrial atmospheric absorption lines in the infrared spectrum from the Sun. In fact many gases were first discovered in the atmosphere during the 1940’s from their absorption features in the infrared solar spectrum. These early optical absorption measurements of the atmosphere using the Sun as a source were made with grating spectrometers and examples of atmospheric gases first detected this way include methane and CO [Migeotte, 1948; 1949]. Continuous or semi-continuous records of infrared solar atmospheric absorption spectra have been made from ground-based Fourier transform spectrometers (FTS) since the late 1970s and early 1980s, when the first ground-based solar-tracking FTS systems were installed at Kitt Peak National observatory in the USA and at the Jungfraujoch Observatory in Switzerland. Initially interest was focused on the detection and quantification of stratospheric trace gases [Rinsland et al., 1986; Zander et al., 1986]. The discovery of the Antarctic ozone hole [Farman et al., 1985] intensified interest in stratospheric chemistry and helped support the establishment of the Network for Detection of Stratospheric Change (NDSC). This global network of instrument sites became operational in 1991 with ground-based FTS amongst the suite of primary techniques being used. Photographs of the instrument at the NDACC site at Wollongong, Australia are shown for illustrative purposes in figure 1 below. Other NDSC instruments are lidars for ozone, temperature, water and aerosols; microwave instruments for ozone, water and chlorine monoxide; UV/Visible spectrograph for ozone and nitrogen dioxide; Dobson/Brewer spectrophotometers for total column

We present a new method for deriving total emissions estimates from large vegetation fires using satellite-based measurements of aerosol optical depth. This method is based upon simultaneous measurements of total column amounts of trace gases and aerosol optical depth of the atmosphere through smoke plumes from Australian fires. These measurements were derived from ground-based solar remote sensing spectrometers in the infrared and UV-visible spectral regions and also provide emission ratios that may be used in more conventional bottom-up estimates of total emissions. Measurements of emissions from Australian forest fires are relatively sparse given the significance of this source to the global emissions budget from biomass burning. Additional measurements of emission ratios of a number of trace gases have been made using open-path FTIR measurements through smoke plumes from hazard reduction burns in New South Wales.

The Great Barrier Reef World Heritage Area contains highly sensitive ecosystems that are threatened by the effects of anthropogenic activity including eutrophication. The nearby sugarcane plantations of tropical north Queensland are fertilised annually and there has been ongoing concern about the magnitude of the loss of applied nitrogen to the environment. Previous studies have considered the potential of rainwater run-off to deposit reactive nitrogen species into rivers and ultimately into the Great Barrier Reef Lagoon, but have neglected the possibility of transport via the atmosphere. This paper reports the results of a modelling study commissioned by Australia’s National Heritage Trust aimed at assessing whether or not atmospheric deposition of reactive nitrogen from Queensland’s sugarcane plantations posed a potential threat to the Great Barrier Reef Lagoon. Atmospheric dispersion modelling was undertaken using The Air Pollution Model, developed by Australia’s Commonwealth Scientific and Industrial Research Organisation. Despite the predominance of onshore southeasterly winds, the dispersion model results indicate that 9% of the time during the sugarcane fertilization season (in the modeled years 2001–2006) the meteorological conditions resulted in emissions from the coastal regions of north Queensland being transported out over the ocean around the Great Barrier Reef. The results suggest that there may be a greater efficiency for transport out over the reef during October than for November and December. For the 2 months that exhibited the greatest potential for transport of coastal pollution to the Great Barrier Reef, the modeled deposition of nitrogen oxides (NOX) into the Great Barrier Reef lagoon was less than 1% of the total emissions from the sugarcane plantations, but was not zero. Our model has a simple chemical scheme that does not cover the full chemistry of all reactive nitrogen compounds and so the results are only indicative of the potential level

We report greenhouse gas concentrations measured on a train covering a north-south transect through central Australia from north to south coast. During the monsoonal wet season we found significant enhancements in methane that correlate well with changing area of wetland inundation in Australian tropical savanna regions. We used a meteorological and air pollution model to quantify the ephemeral wetland fluxes necessary to cause the observed enhancements and estimate the constant Australian tropical wetland emissions. Annual Australian tropical ephemeral wetland fluxes are estimated at 0.4 +/- 0.2 Tg CH4, with permanent wetlands contributing a similar amount, 0.5 +/- 0.2 Tg CH4.

We present analyses of near‐infrared ground‐based Fourier transform infrared solar absorption spectra recorded from a site in Darwin, Northern Territory, Australia (12.4°S, 130.9°E) from August 2005 to June 2008. Total column amounts of carbon monoxide derived from these spectra show a very clear annual cycle, with evidence of transported pollution from Indonesian fires in 2006. Aerosol optical depth measurements from the same site show a similar annual cycle but without exceptional values in 2006, suggesting significant loss of aerosol loading in the transported and aged smoke. In addition, we report the first ever measurements by remote sensing solar Fourier transform infrared of emission ratios with respect to carbon monoxide for formaldehyde (0.022 ± 0.007), acetylene (0.0024 ± 0.0003), ethane (0.0020 ± 0.0003), and hydrogen cyanide (0.0018 ± 0.0003) from Australian savanna fires. These are derived from mid‐infrared spectra recorded through smoke plumes over Darwin on 20 separate days. The only previous measurements of emission ratios for formaldehyde and hydrogen cyanide from Australian savanna fires involved cryogenic trapping and storage of samples that were gathered in very fresh smoke. The results reported here are nearly an order of magnitude higher (but in agreement with laboratory studies), suggesting losses in the collection, storage, or transfer of the gases in the earlier measurements and/or chemical production of these reactive gases within the smoke plumes. Emission ratios for acetylene and ethane from this work are in broad agreement with other literature values.

In this paper we describe a new method for estimating trace gas emissions from large vegetation fires using satellite measurements of aerosol optical depth (AOD) at 550 nm, combined with an atmospheric chemical transport model. The method uses a threshold value to screen out normal levels of AOD that may be caused by raised dust, sea salt aerosols or diffuse smoke transported from distant fires. Using this method we infer an estimated total emission of 15±5 Tg of carbon monoxide, 0.05±0.02 Tg of hydrogen cyanide, 0.11±0.03 Tg of ammonia, 0.25±0.07 Tg of formaldehyde, 0.03±0.01 of acetylene, 0.10±0.03 Tg of ethylene, 0.03±0.01 Tg of ethane, 0.21±0.06 Tg of formic acid and 0.28±0.09 Tg of methanol released to the atmosphere from the Canberra fires of 2003. An assessment of the uncertainties in the new method is made and we show that our estimate agrees (within expected uncertainties) with estimates made using current conventional methods of multiplying together factors for the area burned, fuel load, the combustion efficiency and the emission factor for carbon monoxide. A simpler estimate derived directly from the satellite AOD measurements is also shown to be in agreement with conventional estimates, suggesting that the method may, under certain meteorological conditions, be applied without the complication of using a chemical transport model. The new method is suitable for estimating emissions from distinct large fire episodes and although it has some significant uncertainties, these are largely independent of the uncertainties inherent in conventional techniques. Thus we conclude that the new method is a useful additional tool for characterising emissions from vegetation fires.

The ‘Black Saturday’ fires were a series of devastating bushfires that burned across Victoria, Australia, during February 2009. The smoke plume from Saturday the 7th February, the worst day of the fires, separated from subsequent emissions and persisted for several weeks, providing the opportunity to track the changing composition of the smoke plume as it aged. In this study we have used satellite data from the Ozone Monitoring Instrument (OMI) and the Atmospheric InfraRed Sounder (AIRS) to characterise the emissions of formaldehyde and nitrogen dioxide from the fires. Emission ratios with respect to carbon monoxide are determined for formaldehyde (0.017 ± 0.004 mol.mol-1) and nitrogen dioxide (0.004 ± 0.001 mol.mol-1). Additionally OMI UV Aerosol Index is used to track the smoke plume and infer how the concentration of these gases changes as the smoke ages. Our study suggests that formaldehyde concentrations within the smoke plume increase during the first day before declining to background levels within 2 days after emission. Nitrogen dioxide concentrations show a monotonic decrease reaching background levels about 1 day after emission.

This paper presents a validation study of SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) carbon monoxide (CO) total column measurements from the Iterative Maximum Likelihood Method (IMLM) algorithm using ground-based spectrometer observations from twenty surface stations for the five year time period of 2003–2007. Overall we find a good agreement between SCIAMACHY and ground-based observations for both mean values as well as seasonal variations. For high-latitude Northern Hemisphere stations absolute differences between SCIAMACHY and ground-based measurements are close to or fall within the SCIAMACHY CO 2 precision of 0.2×1018 molecules/cm2 (10%) indicating that SCIAMACHY can observe CO accurately at high Northern Hemisphere latitudes. For Northern Hemisphere mid-latitude stations the validation is complicated due to the vicinity of emission sources for almost all stations, leading to higher ground-based measurements compared to SCIAMACHY CO within its typical sampling area of 8 ×8. Comparisons with Northern Hemisphere mountain stations are hampered by elevation effects. After accounting for these effects, the validation provides satisfactory results

Nitrous oxide (N2O) plays important roles in atmospheric chemistry both as a greenhouse gas and in stratospheric ozone depletion. Isotopic measurements of N2O have provided an invaluable insight into understanding its atmospheric sources and sinks. The preference for 15N fractionation between the central and terminal positions (the “site preference”) is particularly valuable because it depends principally on the processes involved in N2O production or consumption, rather than the 15N content of the substrate from which it is formed. Despite the value of measurements of the site preference, there is no internationally recognized standard reference material of accurately known and accepted site preference, and there has been some lack of agreement in published studies aimed at providing such a standard. Previous work has been based on isotope ratio mass spectrometry (IRMS); in this work we provide an absolute calibration for the intramolecular site preference of 15N fractionation of working standard gases used in our laboratory by a completely independent technique—high-resolution Fourier transform infrared (FT-IR) spectroscopy. By reference to this absolute calibration, we determine the site preference for 25 samples of tropospheric N2O collected under clean air conditions to be 19.8‰ ± 2.1‰. This result is in agreement with that based on the earlier absolute calibration of Toyoda and Yoshida (Toyoda, S. and Yoshida, N. Anal. Chem. 1999, 71, 4711−4718) who found an average tropospheric site preference of 18.7‰ ± 2.2‰. We now recommend an interlaboratory exchange of working standard N2O gases as the next step to providing an international reference standard.

This thesis describes work aimed at improving our knowledge of emissions to the atmosphere from Australian vegetation fires. The thesis contains three main parts. First there is a study to characterise the emissions from forest fires in southeast Australia. This uses ground-based Fourier transform infrared solar absorption spectroscopy, coupled with ultra-violet/visible spectroscopy, to explore the properties of smoke plumes from Australian forest fires that passed over the observation site at Wollongong, in New South Wales, Australia (34.4°S, 150.9°E). The particulate loading in the smoke plumes is characterised by the aerosol optical depth, measured at visible wavelengths. Vertically integrated amounts of a several emitted trace gases are also determined, (limited to those detectable by solar absorption spectroscopy in the infrared). Enhanced trace gas amounts of carbon monoxide, hydrogen cyanide, formaldehyde, ammonia, acetylene, ethylene, ethane, formic acid and methanol were measured in the smoke plumes and quantified via the use of emission ratios. The emission ratios determined in this study indicate that emissions from fires in southeastern Australian forests (which are predominantly eucalypts) are broadly similar to those from other geographical regions except for comparatively low emissions of ethane. The second part of this thesis describes a new method of making estimates of gaseous emissions from fires. Strong correlations between trace gases and aerosol optical depth (AOD) in smoke plumes are used in conjunction with satellite-based measurements of AOD to estimate the total amounts of carbon monoxide and other gases emitted from the Canberra fires of 2003. There are significant difficulties with the new method, in particular the interruption of the satellite record due to clouds or technical problems with the satellite. Nevertheless the estimated emissions of carbon monoxide from the Canberra fires (4.9 – 9.6 Tg), is in agreement with an estimate made

We report the first atmospheric column measurements of methanol made by ground-based solar Fourier transform infrared spectroscopy. The measurements were made through smoke plumes over South Eastern Australia during the Austral summers of 2001/2002 and 2002/2003. There is a strong correlation between the measured column amounts of methanol and simultaneous and co-located measurements of aerosol optical depth. An emission factor for methanol from Australian forest fires of 2.3 ± 0.8 grams per kilogram of dry fuel consumed is estimated by use of the correlations of methanol and carbon monoxide with aerosol optical depth and literature values for the emission factor of carbon monoxide. This agrees well with literature values for emissions measured from extra-tropical forest fires elsewhere in the world. Methanol is clearly an important volatile organic product of forest fires with an emission factor similar to formaldehyde’s and approximately half that of methane.

We report the results of an intercomparison of vertical column amounts of hydrogen chloride (HCl), hydrogen fluoride (HF), nitrous oxide (N2O), nitric acid (HNO3), methane (CH4), ozone (O3), carbon dioxide (CO2) and nitrogen (N2) derived from the spectra recorded by two ground-based Fourier transform infrared (FTIR) spectrometers operated side-by-side using the sun as a source. The procedure used to record spectra and derive vertical column amounts follows the format of previous instrument intercomparisons organised by the Network for Detection of Atmospheric Composition Change (NDACC), formerly known as the Network for Detection of Stratospheric Change (NDSC). For most gases the differences were typically around 3% and in about half of the results the error bars given by the standard deviation of the measurements from each instrument did not overlap. The worst level of agreement was for HF where differences of over 5% were typical. The level of agreement achieved during this intercomparison is a little worse than that achieved in previous intercomparisons between ground-based FTIR spectrometers.