industrial processing and transportation emissions, primarily stemming from palm oil production and related activities, remained consistent throughout the year.
these emissions were quantified by estimating the energy demands for processing and the types of fuels utilized. the study assumed industrial processing required 8 gigajoules per tonne of palm oil, while plantation cultivation and local transport needed approximately 3 gigajoules per tonne of palm oil.
it is estimated that fossil fuels supplied one hundred percent of transportation energy and seventy-five percent of processing energy. the remaining energy needs were met by burning waste products such as empty fruit bunches and shells.
comparisons between p-TOMCAT model outputs from various scenarios and CiTTyCAT calculations revealed similar general trends.
specifically, data points representing a pristine rainforest landscape and an oil palm monoculture landscape were plotted, mirroring the trends observed in box model calculations. while p-TOMCAT calculations did not explore as wide a range of nitrogen oxide (NOx) concentrations as the box model, future integrations are planned to expand this analysis.
figure 5 illustrates the percentage change in surface ozone levels between the rainforest and oil palm emission scenarios for a single day in may. the simulated increase in isoprene and NOx emissions in the oil palm scenario resulted in an approximate eighty percent rise in surface ozone concentrations.
although the absolute modeled ozone mixing ratios in this snapshot did not exceed 34 parts per billion (ppb) in the oil palm scenario, the model indicated significant temporal fluctuations. for instance, at the danum valley site, ozone levels were observed to surpass 40 ppb at multiple points throughout the month.
the most pronounced changes were localized over borneo, with substantial increases in ozone also occurring downwind, with the precise location dependent on daily meteorological conditions.
increases in modeled ozone were also detected in the free troposphere.
at an altitude of approximately 5 kilometers, the model predicted local ozone increases of up to twelve percent on a monthly average for may. in this particular case, the most significant ozone enhancements were observed downwind of borneo, correlating with heightened levels of hydroxyl (OH) radicals and NOx.
therefore, while the most substantial changes were geographically confined, these calculations suggest that the ramifications of land-use transformations extend beyond borneo, leading to minor alterations throughout the free troposphere. it is important to note that only changes in emissions originating from borneo were considered in this analysis.
a more comprehensive assessment, incorporating emission changes across the broader tropics (including africa, south america, and other regions), would likely result in a more pronounced free tropospheric response. the integrations were driven by meteorological analyses, with grid lines indicating 3° × 3° resolution, while the calculations themselves were performed at a finer 1° × 1° resolution.
bukit atur is identified by a large filled circle. the exploratory nature of these experiments, designed to assess sensitivities, is crucial to acknowledge. for example, a landscape entirely dedicated to oil palm represents an extreme scenario but serves as a valuable tool for projecting potential future air quality trajectories.
similarly, previous discussions highlighted several uncertainties within the chemical modeling framework, which necessitate caution when interpreting these calculations. however, it is worth recalling that despite discrepancies between observed and modeled surface composition, the calculated perturbations exhibit greater robustness when subjected to uncertainties in aspects like chemical scheme details, as discussed in section 3b.
the preceding discussion focused on the influence of emission shifts due to land-use alterations on atmospheric chemistry.
isoprene emissions are influenced by a multitude of factors. a well-established relationship exists between isoprene emission rates and light and temperature; higher temperatures generally lead to increased emissions, peaking at approximately 40°c. more recently, a dependence on carbon dioxide (CO2) concentrations has also been identified, demonstrating a reduction in emissions at CO2 levels exceeding current ambient values.
consequently, the overall impact of climate change on isoprene emissions is a result of the interplay between changes in light (due to cloud cover), temperature, and CO2 concentrations. to accurately forecast future atmospheric composition, it is essential to evaluate the relative contributions of land-use change, temperature, and CO2 to emission variations.
in this regard, a regional climate model known as PRECIS was coupled with a biogenic emission model, BVOCEM, to investigate the combined effects of climate and land-use change on biogenic emissions in southeast asia. however, the subsequent impact of these specific scenarios on atmospheric chemistry has yet to be fully explored.
extrapolating current land-use change trends into the future, a study employing the A2 SRES scenarios from the Intergovernmental Panel on Climate Change (IPCC) projected a decrease in the present-day annual mean leaf-area index (L) across southeast asia, particularly in areas designated for oil palm, paddy rice, and other land-use types.
modelled temperatures across the region were projected to increase by approximately 3°c. future projections for other climatic variables, such as precipitation and boundary layer depth, exhibited considerable variability. within the same scenario, incorporating a CO2 emissions factor indicated an inhibition of isoprene emissions by eight percent.
this suggests that the negative influence of elevated CO2 on isoprene emissions effectively counteracted the positive effect of climate change alone. when projected land-use changes were integrated with the combined effects of climate change and the CO2 emissions factor, a projected decrease in future isoprene emissions of sixty-six percent was observed.
land-use forcing alone accounted for a five percent reduction in isoprene emissions when the CO2 emissions factor was included, compared to a nine percent increase in isoprene emissions when the CO2 emissions factor was not considered. these findings imply that future isoprene emissions in the region would be largely modulated by a confluence of competing factors, making precise predictions of future isoprene emissions and their atmospheric chemistry implications challenging.
for several decades, it has been recognized that long-lived anthropogenic halogen species play a significant role in stratospheric chemistry.
major long-lived gases are now subject to regulation under the Montreal Protocol, and their atmospheric abundances have begun to decline. however, it is estimated that an additional 4-6 parts per trillion (ppt) of short-lived bromine compounds are required to balance the bromine budget in the lower stratosphere.
photolysis or oxidation reactions would then release active halogen atoms, which could contribute to stratospheric ozone depletion. transport from the lower atmosphere to the tropical tropopause layer is most rapid over the maritime continent. characterizing the background concentrations of these short-lived compounds and their variability in southeast asia is a critical research objective, to which the OP3 research has made a valuable contribution.
in contrast to the stratosphere, our comprehension of the role of halogens in the global troposphere is still evolving rapidly.
it has been established for some time that brominated compounds are responsible for sporadic, rapid ozone depletion in the polar boundary layer. furthermore, substantial evidence now indicates a broader role for reactive halogen chemistry throughout remote oceanic boundary layers in tropical and mid-latitudes, and potentially in the global free troposphere.
understanding the sources of these reactive species and their global implications is now a paramount research question. the primary identified sources of reactive bromine and iodine species to the troposphere include emissions of organic halocarbons from macroalgae and sea salt aerosol, which represents the most significant source of bromine.
there is also some indication that rainforests may contribute a minor natural source. short-lived halocarbons, in particular, remain poorly understood in terms of their global flux. it is clear that further research is needed to reconcile the wide range of existing estimates and to refine these figures.
the influence of halogens could evolve in the future.
oceanic halocarbon sources likely depend on ocean temperature and climate-driven biological processes. additionally, ocean sources of halocarbons are influenced by wind stress on the ocean surface. transport pathways and rates from source to sink could also change in a future climate.
for instance, preliminary calculations suggest an increase in the convective transport of short-lived, ozone-depleting halogens to the lowermost stratosphere later this century. an additional factor is the rapidly expanding seaweed cultivation industry, with over [number] hectares of seaweed farms now established around semporna, off the northeast coast of sabah.
several research groups conducted measurements of halocarbons during the OP3 campaign, the results of which are presented herein. two specific studies are examined: the first explored the source strength of bromoform in southeast asia, while the second determined the total amount of short-lived bromine in the maritime continent's boundary layer, which could potentially be transported to the stratosphere via deep convection.
continuous measurements of a spectrum of halocarbons, ranging from chlorofluorocarbons (CFCs) to very short-lived halocarbons, were performed during OP3 utilizing gas chromatographs equipped with electron capture (GC-ECD) and mass spectrometer (GC-MS) detectors.
two µDirac GC-ECDs were deployed in sabah. one was stationed at the bukit atur global atmospheric watch (GAW) site in danum valley, while the other was used in a series of brief, exploratory deployments at various rainforest locations and the coastal town of kunak. measurements were conducted during two distinct periods, from april to august [year].
halocarbons, including short-lived tracers with both biogenic and anthropogenic origins, were measured with precisions ranging from ±1% for CCl4 to ±9% for CH3I. approximately 35-40 atmospheric samples were collected daily, interspersed with calibration gas samples and blank runs.
the calibration gas utilized was from an NOAA earth system research laboratory standard, collected and calibrated in december [year]. typical uncertainty in the calibration gas was ±0.1% for CFCs and other long-lived halocarbons, and ±5% to ±20% for short-lived halocarbons (b.
hall, personal communication). a GC-MS system, primarily operating in negative ion chemical ionization mode, was co-located at bukit atur, conducting measurements during both periods. a second GC-MS was employed to analyze whole air samples collected by the BAe aircraft during the july detachment.
the ground-based GC-MS measurements were taken at hourly intervals with a typical precision of less than ±5%. calibrations for other bromochlorocarbons were based on a university of east anglia scale.
measurements of CHBr3 at bukit atur during OP3 ranged from approximately 0.1 to 0.3 ppt.
good consistency was observed between the two µDirac GC-ECDs and the GC-MS measurements. one of the µDirac instruments conducted measurements at various locations within the danum valley site to investigate potential variability, including the possibility of localized sources.
no definitive evidence of localized sources was found, but investigations are ongoing. one of the µDiracs was also deployed for a few days at kunak, a coastal site situated approximately 50 km from bukit atur, located on a bay abundant with macroalgae. figure 6 presents measurements from the two instruments during this period, illustrating a distinct difference in the distribution of concentrations compared to those recorded at bukit atur.
background measurements at kunak ranged between 2 and 5 ppt, exhibiting greater variability than at bukit atur. additionally, a small number of excursions to significantly higher concentrations, reaching up to 60 ppt, were recorded when the local wind was onshore, strongly suggesting the influence of very localized sources.
figure 6 displays the concentration of CHBr3 (in ppt) measured at danum valley and kunak by the µDirac GC.
blue symbols represent measurements taken with the instrument consistently deployed at danum valley. red symbols denote concentrations measured by the instrument that was deployed at kunak between june 21 and 25 but was otherwise situated at danum valley.
these data were analyzed using a range of numerical models to elucidate potential sources and the origin of the concentration gradient observed between the coast and the bukit atur site. the models corroborate that during this period, the air sampled at these locations had traversed biologically rich oceanic and coastal regions, identified as likely source areas.
minor variations in atmospheric transport and differing proximity to emission sources can account for the observed differences in background concentrations. given the short lifetime of CHBr3 (approximately two weeks), determining a global source strength solely from measurements at a single location is not feasible.
a network of observation sites, particularly in tropical regions, is therefore essential. however, the OP3 data allows for the derivation of a localized source magnitude for southeast asia, estimated to be between 21 and 50 Gg CHBr3 yr−1. these figures represent reductions compared to a previous estimate.
considering the significance of the maritime continent for global halogen sources and transport, this newly established range for the local source strength provides a crucial constraint on overall global emissions. our current best estimate stands at [number] Gg CHBr3 yr−1, with probable upper and lower limits ranging from approximately [lower limit] to [upper limit] Gg CHBr3 yr−1, according to warwick et al.
following the OP3 campaign, one of the µDirac GC-ECDs has remained at bukit atur, while the other has been relocated to tawau, a coastal area situated approximately 70 km south of bukit atur. over two years of quasi-continuous measurements of various halocarbons have now been collected.
these measurements are being augmented by new tropical deployments of µDirac, which will facilitate a more precise estimation of source strength and variability.
the total quantity of organically bound bromine is a significant factor for stratospheric and tropospheric halogen chemistry, as it represents the amount of bromine available for release and subsequent participation in atmospheric reactions.
during july [year], five bromine-containing species were measured by GC-MS at danum valley: CHBr3, CH2Br2, CHBrCl2, CHBr2Cl, and CH2BrCl. the summed mixing ratios of bromine within these compounds varied between 5 and 10 ppt, with an average of 7 ppt. over ninety percent of this total was accounted for by CHBr3, CH2Br2, or CHBrCl2.
these findings provide a degree of constraint on the overall concentration of short-lived bromine species that could be transported into the lower stratosphere. detailed modeling will be necessary to ascertain the extent to which this bromine could reach the stratosphere.
furthermore, the variability discussed in section 6a must be considered, and for a more robust constraint, the entire annual cycle should be analyzed, ideally from multiple tropical locations. the amount of bromine reaching the stratosphere could fluctuate in the future, depending on changes in both emissions (e.g., due to increased seaweed farming) and the speed of transport (e.g., enhanced convection).
as both of these processes could be influenced by future climate conditions, further research into these fundamental mechanisms is warranted.
we have presented select findings from the OP3 campaign conducted in sabah during [year], which enable us to investigate the impact of localized environmental changes on atmospheric composition at broader spatial scales.
localized measurements of atmospheric constituents were analyzed within the framework of both box and global atmospheric models. the critical importance of accurately representing physical processes such as mixing, deposition, and emissions has been underscored.
model-based investigations into land-use change corroborate earlier studies by hewitt et al. further intensification of oil palm agriculture in southeast asia, and the tropics more generally, could significantly affect air quality, with changes in NOx emissions emerging as the most influential factor.
substantial increases in NOx and volatile organic compounds (VOCs) are projected to result in significant ozone alterations. based on the specific emission scenarios developed, global model calculations suggest a potential localized increase in ozone of approximately fifty percent, with smaller impacts also calculated in the free troposphere.
similar to many other instances involving shifts in industrial practices, a comprehensive environmental life cycle assessment of land-use changes is imperative. the maritime continent is characterized by very strong deep convective activity, meaning that even short-lived chemical species have the potential to be transported to the lower stratosphere.
measurements of short-lived brominated compounds in the vicinity of sabah highlight the importance of oceanic and, particularly, coastal emission sources. elevated concentrations were frequently detected when local atmospheric circulation patterns trapped air within the boundary layer over regions with high potential emissions, allowing concentrations to accumulate over time.
the global significance of these concentrations, for example, is estimated to be around 7 ppt for total short-lived bromine concentrations measured at the surface during OP3, thereby imposing a constraint on the quantity of these species that can ascend to the lower stratosphere.
we extend our gratitude to the governments of malaysia and sabah for granting permission to conduct research in malaysia.
we also thank the malaysian meteorological department (MMD), now Met Malaysia, for facilitating access to the bukit atur global atmosphere watch station and for providing their long-term ozone record. this research was also supported by a british council PMI2 grant.
we acknowledge the receipt of data from the AATSR World Fire Atlas, provided by the Data User Element of the European Space Agency. this paper constitutes publication no. [publication number]. search pmc full-text archive search in pmc journal list user guide new try this search in pmc beta search.
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