Measurements and modelling of emissions from biomass burning in Australia

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 by existing techniques. The addition of another tool for making estimates of gaseous emissions from biomass burning is useful for corroborating existing techniques, especially since the sources ofuncertainties inherent in the different techniques are largely independent of one another. The third part of the thesis is a study to characterise the emissions from savanna fires in the tropical north of Australia. Again ground-based Fourier transform infrared solar absorption spectroscopy is used with automated measurements in the near infrared from a site in Darwin, Northern Territory, Australia, (12.4°S, 130.9°E). Alternatively measurements in the mid infrared can be made by overriding the automated system, and this has been done when there is evidence of significant smoke plumes in the area. Total column amounts of carbon monoxide from Darwin from 2005-2008 show a very clear annual cycle, with evidence of transported pollution from Indonesian fires in 2006. The time series agrees within the expected uncertainties with measurements of carbon monoxide derived from the MOPITT satellite instrument, giving greater confidence to MOPITT retrievals in the tropics. Mid infrared spectra have been recorded through smoke plumes over Darwin on 20 separate days, yielding column amounts of carbon monoxide, formaldehyde, acetylene, ethane and hydrogen cyanide and emission ratios with respect to carbon monoxide for the four latter gases from tropical north Australian savanna fires. Emission ratios for acetylene and ethane from this work are in broad agreement with other literature values, whilst emission ratios for formaldehyde and hydrogen cyanide are significantly higher than the only previous field measurements from Australian savannas (but in agreement with laboratory studies) suggesting storage losses in the earlier study

Remote Sensing of Atmospheric Trace Gases by Ground-Based Solar Fourier Transform Infrared Spectroscopy

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 ozone and regular ozone sondes. This resulted in a huge increase in the number of infrared solar absorption measurements being made around the globe during the next few years, e.g. [Bell et al., 1994; Bell et al., 1996; Bell et al., 1998; Blumenstock et al., 1997; David et al., 1993; Griffith et al., 1998; Jones et al., 1994; Liu et al., 1992; Mahieu et al., 1995; Notholt, 1994; Notholt et al., 1997; Toon et al., 1999; Toon et al., 1995; Zander et al., 1994]. More recently interest in atmospheric chemistry has been focused on tropospheric pollution and anthropogenic emissions of greenhouse gases [Barret et al., 2003; Jones et al., 2009; Mahieu et al., 1995; Nagahama et al., 2007; Paton-Walsh et al., 2008; Rinsland et al., 2000; Rinsland et al., 2001; Rinsland et al., 2002; Rinsland et al., 2008; Warneke et al., 2006; Zhao et al., 2000; Zhao et al., 2002]. As a result, the NDSC has changed its emphasis and name to the Network for Detection of Atmospheric Composition and Change (NDACC) – see http://www.ndacc.org/. As well as an ever increasing number of sites in the global network the new millennium has seen an expansion into the near infrared spectra region in an effort to provide extremely accurate and precise measurements of carbon dioxide. The Total Column Carbon Observing Network (TCCON) was established to help characterise biogenic and oceanic sources and sinks of greenhouse gases to and from the atmosphere and to validate current and future satellite based measurements (http://www.tccon.caltech.edu/ ). In this chapter the reader will get a brief introduction to the basic theory behind the retrieval of atmospheric trace gas amounts from atmospheric solar infrared transmission spectra and an overview of the previous successes and current challenges in this field of research

An Intercomparison of Ground-based Solar FTIR Measurements of Atmospheric Gases at Eureka, Canada

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

Absolute calibration of the intramolecular site preference of 15N fractionation in tropospheric N2O by FT-IR spectroscopy

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

Transport of NOX emissions from sugarcane fertilisation into the Great Barrier Reef Lagoon

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 levels of deposition. Nevertheless, our study shows that small amounts of NOX that originate from sugarcane fertilization may be transported and dry deposited into the Great Barrier Reef lagoon. Other pathways not included in the modeling scheme may provide a more efficient transport mechanism. Whilst modern practices for the application of fertilizer to sugarcane plantations have drastically reduced emissions, the potential efficiency of transport of pollutants via the atmosphere may be of concern for other more highly polluting agricultural industries

Trace gas emissions from savanna fires in northern Australia

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

Trace Gas Emissions from Biomass Burning inferred from Aerosol Optical Depth

We have observed strong correlations between simultaneous and co-located measurements of aerosol optical depth and column amounts of carbon monoxide, hydrogen cyanide, formaldehyde and ammonia in bushfire smoke plumes over SE Australia during the Austral summers of 2001/2002 and 2002/2003. We show how satellite-derived aerosol optical depth maps may be used in conjunction with these correlations to determine the total amounts of these gases present in a fire-affected region. This provides the basis of a method for estimating total emissions of trace gases from biomass burning episodes using visible radiances measured by satellite

Satellite and ground-based measurements of XCO2 in a remote semiarid region of Australia

In this study, we present ground-based measurements of column-averaged dry-air mole fractions (DMFs) of CO2 (or XCO2) taken in a semiarid region of Australia with an EM27/SUN portable spectrometer equipped with an automated clamshell cover. We compared these measurements to space-based XCO2 retrievals from the Greenhouse Gases Observing Satellite (GOSAT). Side-by-side measurements of EM27/SUN with the Total Carbon Column Observing Network (TCCON) instrument at the University of Wollongong were conducted in 2015-2016 to derive an XCO2 scaling factor of 0.9954 relative to TCCON. Although we found a slight drift of 0.13 % over 3 months in the calibration curve of the EM27/SUN vs. TCCON XCO2, the alignment of the EM27/SUN proved stable enough for a 2-week campaign, keeping the retrieved Xair values, another measure of stability, to within 0.5 % and the modulation efficiency to within 2 %. From the measurements in Alice Springs, we confirm a small bias of around 2 ppm in the GOSAT M-gain to H-gain XCO2 retrievals, as reported by the NIES GOSAT validation team. Based on the reported random errors from GOSAT, we estimate the required duration of a future campaign in order to better understand the estimated bias between the EM27/SUN and GOSAT. The dataset from the Alice Springs measurements is accessible at https://doi.org/10.4225/48/5b21f16ce69bc (Velazco et al., 2018)

NDACC harmonized formaldehyde time-series from 21 FTIR stations covering a wide range of column abundances

Among the more than 20 ground-based FTIR (Fourier transform infrared) stations currently operating around the globe, only a few have provided formaldehyde (HCHO) total column time series until now. Although several independent studies have shown that the FTIR measurements can provide formaldehyde total columns with good precision, the spatial coverage has not been optimal for providing good diagnostics for satellite or model validation. Furthermore, these past studies used different retrieval settings, and biases as large as 50 % can be observed in the HCHO total columns depending on these retrieval choices, which is also a weakness for validation studies combining data from different ground-based stations. For the present work, the HCHO retrieval settings have been optimized based on experience gained from past studies and have been applied consistently at the 21 participating stations. Most of them are either part of the Network for the Detection of Atmospheric Composition Change (NDACC) or under consideration for membership. We provide the harmonized settings and a characterization of the HCHO FTIR products. Depending on the station, the total systematic and random uncertainties of an individual HCHO total column measurement lie between 12 % and 27 % and between 1 and 11×1014 molec cm−2, respectively. The median values among all stations are 13 % and 2.9×1014 molec cm−2 for the total systematic and random uncertainties. This unprecedented harmonized formaldehyde data set from 21 ground-based FTIR stations is presented and its comparison with a global chemistry transport model shows consistency in absolute values as well as in seasonal cycles. The network covers very different concentration levels of formaldehyde, from very clean levels at the limit of detection (few 1013 molec cm−2) to highly polluted levels (7×1016 molec cm−2). Because the measurements can be made at any time during daylight, the diurnal cycle can be observed and is found to be significant at many stations. These HCHO time series, some of them starting in the 1990s, are crucial for past and present satellite validation and will be extended in the coming years for the next generation of satellite missions.This study has been supported by the ESA PRODEX project TROVA (2016–2018) funded by the Belgian Science Policy Office (Belspo)

NDACC harmonized formaldehyde time series from 21 FTIR stations covering a wide range of column abundances

Among the more than 20 ground-based FTIR (Fourier transform infrared) stations currently operating around the globe, only a few have provided formaldehyde (HCHO) total column time series until now. Although several independent studies have shown that the FTIR measurements can provide formaldehyde total columns with good precision, the spatial coverage has not been optimal for providing good diagnostics for satellite or model validation. Furthermore, these past studies used different retrieval settings, and biases as large as 50% can be observed in the HCHO total columns depending on these retrieval choices, which is also a weakness for validation studies combining data from different ground-based stations. For the present work, the HCHO retrieval settings have been optimized based on experience gained from past studies and have been applied consistently at the 21 participating stations. Most of them are either part of the Network for the Detection of Atmospheric Composition Change (NDACC) or under consideration for membership. We provide the harmonized settings and a characterization of the HCHO FTIR products. Depending on the station, the total systematic and random uncertainties of an individual HCHO total column measurement lie between 12% and 27% and between 1 and 11x1014 moleccm-2, respectively. The median values among all stations are 13% and 2.9x1014 moleccm-2 for the total systematic and random uncertainties. This unprecedented harmonized formaldehyde data set from 21 ground-based FTIR stations is presented and its comparison with a global chemistry transport model shows consistency in absolute values as well as in seasonal cycles. The network covers very different concentration levels of formaldehyde, from very clean levels at the limit of detection (few 1013moleccm-2) to highly polluted levels (7x1016moleccm-2). Because the measurements can be made at any time during daylight, the diurnal cycle can be observed and is found to be significant at many stations. These HCHO time series, some of them starting in the 1990s, are crucial for past and present satellite validation and will be extended in the coming years for the next generation of satellite missions