Transport Of Biomass Burning Emissions Research Articles

Diverging trends in aerosol sulfate and nitrate measured in the remote North Atlantic in Barbados are attributed to clean air policies, African smoke, and anthropogenic emissions.

Sulfate and nitrate aerosols degrade air quality, modulate radiative forcing and the hydrological cycle, and affect biogeochemical cycles, yet their global cycles are poorly understood. Here, we examined trends in 21 years of aerosol measurements made at Ragged Point, Barbados, the easternmost promontory on the island located in the eastern Caribbean Basin. Though the site has historically been used to characterize African dust transport, here we focused on changes in nitrate and non-sea-salt (nss) sulfate aerosols from 1990-2011. Nitrate aerosol concentrations averaged over the entire period were stable at 0.59 μg m-3 ± 0.04 μg m-3, except for elevated nitrate concentrations in the spring of 2010 and during the summer and fall of 2008 due to the transport of biomass burning emissions from both northern and southern Africa to our site. In contrast, from 1990 to 2000, nss-sulfate decreased 30% at a rate of 0.023 μg m-3 yr-1, a trend which we attribute to air quality policies enacted in the United States (US) and Europe. From 2000-2011, sulfate gradually increased at a rate of 0.021 μg m-3 yr-1 to pre-1990s levels of 0.90 μg m-3. We used the Community Multiscale Air Quality (CMAQ) model simulations from the EPA's Air QUAlity TimE Series (EQUATES) to better understand the changes in nss-sulfate after 2000. The model simulations estimate that increases in anthropogenic emissions from Africa explain the increase in nss-sulfate observed in Barbados. Our results highlight the need to better constrain emissions from developing countries and to assess their impact on aerosol burdens in remote source regions.

Quantifying evolution of soot mixing state from transboundary transport of biomass burning emissions

Incomplete combustion of fossil fuels and biomass burning emit large amounts of soot particles into the troposphere. The condensation process is considered to influence the size (Dp) and mixing state of soot particles, which affects their solar absorption efficiency and lifetimes. However, quantifying aging evolution of soot remains hampered in the real world because of complicated sources and observation technologies. In the Himalayas, we isolated soot sourced from transboundary transport of biomass burning and revealed soot aging mechanisms through microscopic observations. Most of coated soot particles stabilized one soot core under Dp<400nm, but 34.8% of them contained multi-soot cores (nsoot ≥ 2) and nsoot increased 3-9 times with increasing Dp. We established the soot mixing models to quantify transformation from condensation- to coagulation-dominant regime at Dp≈ 400nm. Studies provide essential references for adopting mixing rules and quantifying the optical absorption of soot in atmospheric models.

The Impact of Long-Range Transport of Biomass Burning Emissions in Southeast Asia on Southern China

The long-range transport of biomass burning pollutants from Southeast Asia has a significant impact on air quality in China. In this study, the Moderate Resolution Imaging Spectroradiometer (MODIS) fire data and aerosol optical depth (AOD) products and the Tropospheric Monitoring Instrument (TROPOMI) carbon monoxide (CO) data were used to analyze the impact of air pollution caused by biomass burning in Southeast Asia on southern China. Results showed that Yunnan, Guangdong and Guangxi were deeply affected by biomass burning emissions from March to April during 2016–2020. Comparing the data for fires on the Indochinese Peninsula and southern provinces of China, it is obvious that the contribution of pollutants emitted by local biomass burning in China to air pollution is only a small possibility. The distribution of CO showed that the overall emissions increased greatly from March to April, and there was an obvious transmission process. In addition, the MODIS AOD in areas close to the national boundary of China is at a high level (&gt;0.6), and the AOD in the southwest of Guangxi province and the southeast of Yunnan Province is above 0.8. Combined with a typical air pollution event in southern China, the UVAI combined with wind direction and other meteorological data showed that the pollutants were transferred from the Indochinese Peninsula to southern China under the southwest monsoon. The PM2.5 data from ground-based measurements and backward tracking were used to verify the pollutant source of the pollution event, and it was concluded that the degree of pollution in Yunnan, Guangxi and Guangdong provinces was related to the distance from the Indochinese Peninsula. Results indicate that it is necessary to carry out in-depth research on the impact of cross-border air pollution transport on domestic air quality as soon as possible and to actively cooperate with foreign countries to carry out pollution source research and control.

Light absorption properties of black and brown carbon in winter over the North China Plain: Impacts of regional biomass burning

Biomass burning (BB) is an important source of brown carbon (BrC) and black carbon (BC), which are two key highly absorbent substances in atmospheric particles and can have a substantial positive impact on the climate radiative forcing. This study presents the light absorption properties of BC and BrC in PM2.5 during the winter in Beijing, with a discussion on the regional transportation of the light absorption of BC and BrC. Relatively high levels of the light absorption coefficient (Absλ) of BC, BrC, and the chemical compounds were found during haze episodes. The average AbsBC at λ = 880 and AbsBrC at λ = 370 during the haze period were as high as 4.4 and 2.9 times higher than those during the clean periods. The biomass burning tracer levoglucosan was significantly correlated with AbsBC880 (R2 = 0.53, P < 0.001), AbsBrC370 (R2 = 0.47, P < 0.001) and AbsBC(BB) (R2 = 0.69, P < 0.001). The average contributions of biomass burning to organic carbon (OC) and AbsBC were 33% and 48%, respectively, indicating that biomass burning was an important source of light-absorbing substances in the atmosphere. Concentration-weighted trajectory (CWT) analyses using TrajStat software also demonstrated that regional transport of biomass burning emissions from the northwestern and southwestern areas, which cover the intense fire spots from VIIRS, had a considerable influence on the light absorption properties of PM2.5 and even haze formation in Beijing during the winter.

Differential Effects of the COVID-19 Lockdown and Regional Fire on the Air Quality of Medellín, Colombia

Governments’ responses to the COVID-19 pandemic provide a unique opportunity to study the effects of restricted socioeconomic activity on air quality. Here, we study the changes in air pollution levels during the lockdown in Medellín and its metropolitan area, Colombia, for periods with and without enhanced regional fire activity, considering the effects of meteorology using random forest and multiple linear regression methods. The lockdown measures, which reduced mean traffic volume by 70% compared to 2016–2019, resulted in reductions for PM2.5 (50–63%), PM10 (59–64%), NO (75–76%), NO2 (43–47%), and CO (40–47%), while O3 concentration increased by 19–22%. In contrast, when fire activity was high, the effects of the lockdown on air quality were shadowed by the long-range transport of biomass burning emissions, increasing fine particulate matter and ozone. This study shows that healthier levels are achievable through significant efforts from decision-makers and society. The results highlight the need to develop integral measures that do not only consider reductions in the local emissions from transportation and industry, but also the role of fire activity in the region, as well as the difficulties of achieving reductions in ozone from measures that are effective at reducing primary pollutants.

Aircraft measurements of aerosol and trace gas chemistry in the eastern North Atlantic

Abstract. The Aerosol and Cloud Experiment in the Eastern North Atlantic (ACE-ENA) investigated properties of aerosols and subtropical marine boundary layer (MBL) clouds. Low subtropical marine clouds can have a large effect on Earth's radiative budget, but they are poorly represented in global climate models. In order to understand their radiative effects, it is imperative to understand the composition and sources of the MBL cloud condensation nuclei (CCN). The campaign consisted of two intensive operation periods (IOPs) (June–July 2017 and January–February 2018) during which an instrumented G-1 aircraft was deployed from Lajes Field on Terceira Island in the Azores, Portugal. The G-1 conducted research flights in the vicinity of the Atmospheric Radiation Measurement (ARM) Eastern North Atlantic (ENA) atmospheric observatory on Graciosa Island. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and Ionicon proton-transfer-reaction mass spectrometer (PTR-MS) were deployed aboard the aircraft, characterizing chemistry of non-refractory aerosol and trace gases, respectively. The eastern North Atlantic region was found to be very clean, with an average non-refractory submicrometer aerosol mass loading of 0.6 µg m−3 in the summer and 0.1 µg m−3 in the winter, measured by the AMS. Average concentrations of the trace reactive gases methanol and acetone were 1–2 ppb; benzene, toluene and isoprene were even lower, &lt;1 ppb. Mass fractions of sulfate, organics, ammonium and nitrate in the boundary layer were 69 %, 23 %, 7 % and 1 % and remained largely similar between seasons. The aerosol chemical composition was dominated by sulfate and highly processed organics. Particulate methanesulfonic acid (MSA), a well-known secondary biogenic marine species, was detected, with an average boundary layer concentration of 0.021 µg m−3, along with its gas-phase precursor, dimethyl sulfide (DMS). MSA accounted for no more than 3 % of the submicron, non-refractory aerosol in the boundary layer. Examination of vertical profiles of aerosol and gas chemistry during ACE-ENA reveals an interplay of local marine emissions and long-range-transported aged aerosol. A case of transport of biomass burning emissions from North American fires has been identified using back-trajectory analysis. In the summer, the non-refractory portion of the background CCN budget was heavily influenced by aerosol associated with ocean productivity, in particular sulfate formed from DMS oxidation. Episodic transport from the continents, particularly of biomass burning aerosol, periodically increased CCN concentrations in the free troposphere. In the winter, with ocean productivity lower, CCN concentrations were overall much lower and dominated by remote transport. These results show that anthropogenic emissions perturb CCN concentrations in remote regions that are sensitive to changes in CCN number and illustrate that accurate predictions of both transport and regional aerosol formation from the oceans are critical to accurately modeling clouds in these regions.

Source Contribution of Firecrackers Burst vs. Long-Range Transport of Biomass Burning Emissions Over an Urban Background

This study reports on the high-resolution data set of ground-level O3, surface-bound polycyclic aromatic hydrocarbons (SB-PAHs), and particle's number concentrations (range: 10 to 1,000 nm, referred to as condensation nucleus concentration: CNC) during a Diwali festival campaign (conducted from 08th to 16th Nov.2015) at Kanpur location. In this study, we have made an attempt to assess the change in atmospheric composition and chemistry (based on SB-PAHs, O3, and CNC) during Diwali festival (11th Nov.) and compared the results with pre-Diwali (08th−10th Nov.) and post-Diwali (12th−16th Nov.) scenarios. The wind pattern and cluster analysis have revealed a quite similar feature that from 10th to 16th of November the prevailed winds were north-westerly (NW). It is noteworthy that NW-winds during post-monsoon season (Oct–Nov) favors the long-range transport of biomass burning emissions (LRT-BB) from its source region in upwind Indo-Gangetic Plain (IGP). The influence of LRT-BB emissions at the receptor site during Diwali and post-Diwali period was reflected by the substantial increase in average concentrations of PM2.5, O3 and CNC (difference has been ascertained from a two-tailed t-test). The Lenshchow-type analysis revealed that the firecrackers (FC) burst and LRT-BB emissions have lead to increase the concentrations of CNC by 54% and 86%, respectively over the urban background level. On the other hand, the FC burst and LRT-BB increased the concentrations of O3 by 12% and 31% (over the urban background), respectively. Lenschow-type analysis revealed that FC burst and LRT-BB increased the daily PM2.5 concentration by 11% and 36%, respectively over its urban background level (286 μg m−3). However, the SB-PAHs concentrations were found to be decreased by 6% and 2%, respectively, during the FC burst activity and LRT-BB emissions. Based on the observations pertaining to the decrease in SB-PAHs concentrations from the Lenschow-type analysis and anti-correlation between SB-PAHs and O3 the heterogeneous-phase chemical reactivity and loss of SB-PAHs has been inferred in this study.

Chemical characterization of wintertime aerosols over the Arabian Sea: Impact of marine sources and long-range transport

Abstract We examined here the compositional characteristics of total suspended particulate (TSP) samples collected along the east coast of the Arabian Sea during a winter cruise (SS379: 6–24 December 2018) to understand the extent of influence of air pollutants from terrestrial sources. The TSP samples (N = 17) were analyzed for water-soluble inorganic species (WSIS), elemental carbon (EC), organic carbon (OC) and water-soluble organic carbon (WSOC). Backward air mass trajectories and satellite-based fire counts revealed an influence of long-range transport of biomass burning emissions in the Indo-Gangetic Plain and southern India. Anthropogenic (82–97%) SO42− is the most abundant WSIS followed by Na+ and/or NH4+. Ambient EC loadings (0.5–2.4 μg m−3) and OC/EC ratios (2.5–10.5) are higher than usually expected for fossil-fuel combustion sources. Low mass ratios of NO3−/non-sea-salt SO42− (0.08–0.49), as well as high ratios of nss-K+/EC (0.14–1.18) and WSOC/OC (0.30–0.74), highlight the significance of coal combustion and biomass burning emissions in the regional influx of air pollutants to the Arabian Sea. The multiple linear regression analysis has indicated strong correlations among sea salt components (Na+, Cl− and Mg2+), carbonaceous components (OC, EC and WSOC), and anthropogenic WSIS (NH4+ and SO42−). Furthermore, we used minimum R-squared technique based primary OC/EC ratio in the EC-tracer method to estimate the contribution of secondary organic carbon (SOC) to OC (7–61%) and TSP mass (0.7–11%). Overall, the composition of TSP is characterized by 21 ± 10% of particulate organic matter, 2.3 ± 1.1% of EC, 21 ± 9% of anthropogenic WSIS and 43 ± 15% of unidentified fraction including dust. This study has implications for understanding the evolving nature of secondary inorganic and organic aerosols in the continental outflows.

Black carbon and its impact on air quality in two semi-rural sites in Southern Italy near an oil pre-treatment plant

Abstract One-year-long data (October 2017–October 2018) of the equivalent black barbon (EBC), absorption Angstrom exponent (AAE), and gaseous compound concentrations in two semi-rural sites in the Agri Valley, Southern Italy, were analyzed. This study aimed to assess the effects of combustion emissions on the air quality and people's health in these sites. The first measurement site, VZI, is located close to the plant, whereas the second is in Grumento, one of the towns at the edge of the valley, approximately 3 km away from the COVA. The emissions mainly originate from the biggest European on-shore pre-treatment plant of crude oil, the Centro Olio Val d’Agri (COVA), which hosts three incinerators and three torches continuously burning. EBC and gaseous pollutants from the COVA mainly affect the area close to the plant. A reduced effect is observed in Grumento where the AAE analysis highlighted the contribution of local domestic heating as an additional source during the cold season. A procedure combining EBC measurements, high-resolution fire satellite visible/infrared imaging radiometer (VIIRS) data, and hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) back-trajectories allowed the identification of the measurement days influenced by both regional and transboundary transport of biomass burning emissions. The identified days were mostly in July, August, and October 2018. The comparison between EBC and PM2.5 data, only available for the Grumento site, showed a good correlation (R2 = 0.6 on a yearly basis), revealing the relevant contribution of the EBC to the fine particulate matter at the site. Finally, a risk communication methodology was applied to associate the number of daily passively smoked cigarettes (PSC) to the measured EBC concentrations. The daily PSC were 2.8 for VZI, and 1.4 for Grumento, which are closer to the results at the remote sites (0.7) than those at the urban sites (10.1≤ PSC≤ 159).

Light absorption, fluorescence properties and sources of brown carbon aerosols in the Southeast Tibetan Plateau

Brown carbon (BrC) has been proposed as an important driving factor in climate change due to its light absorption properties. However, our understanding of BrC’s chemical and optical properties are inadequate, particularly at remote regions. This study conducts a comprehensive investigation of BrC aerosols in summer (Aug. 2013) and winter (Jan. 2014) at Southeast Tibetan Plateau, which is ecologically fragile and sensitive to global warming. The concentrations of methanol-soluble BrC (MeS-BrC) are approximately twice of water-soluble BrC (WS-BrC), demonstrating the environmental importance of water-insoluble BrC are previously underestimated with only WS-BrC considered. The mass absorption efficiency of WS-BrC (0.27–0.86 m2 g−1) is lower than those in heavily polluted South Asia, indicating a distinct contrast between the two sides of Himalayas. Fluorescence reveals that the absorption of BrC is mainly attributed to humic-like and protein-like substances, which broaden the current knowledge of BrC’s chromophores. Combining organic tracer, satellite MODIS data and air-mass backward trajectory analysis, this study finds BrC is mainly derived from bioaerosols and secondary formation in summer, while long-range transport of biomass burning emissions in winter. Our study provides new insights into the optical and chemical properties of BrC, which may have implications for environmental effect and sources of organic aerosols.

Seasonal and spatial variations of optical properties of light absorbing carbon and its influencing factors in a typical polluted city in Yangtze River Delta, China

A major challenge in understanding radiative forcing of aerosols is accurately monitoring the light absorbing components and clarifying the main reasons of their spatial and temporal variations. In this study, the optical properties of light-absorbing carbon (LAC) in aerosols were measured over one year and the impacts from various emission sources and other influencing factors were analyzed at three sites (suburban (NJU), urban (PAES) and industrial (NUIST) in Nanjing, a typical polluted city in eastern China. With an improved method that combines online and offline techniques, we revised the multiple scattering correction factors and significantly reduced the uncertainty in measurement of absorption coefficients of black carbon (BC). The result reveals the necessity of developing the regional dependent factor for estimation of BC absorption. Relatively large mass absorption efficiency (MAE) of BC was found in summer and industrial region (NUIST), and the mixing state and coating relevant with secondary aerosol formation were the main reasons for such seasonal and site dependent variations. Distinct seasonal variations existed in the MAE of brown carbon (BrC) at NJU. In the winter, BrC from primary emissions such as diesel vehicles had a stronger absorption ability than that from secondary aerosol formation. The lowest MAE values of BrC appeared in summer, reflecting the formation of the non-absorbing biogenic secondary organic aerosol, and the effect of photobleaching. At the urban site PAES, BrC was expected to be mainly from gasoline vehicles and transport of biomass burning emissions, and had a stronger light absorbing ability than the other two sites. The results of simultaneous observations at NJU and PAES indicated that the formation of fresh secondary organic aerosol enhanced the optical absorption of BC but reduced that of BrC. The impacts of various influencing factors on LAC provided effective ways to alleviate their regional radiative forcing at the city scale.

Spatial variability and possible sources of acetate and formate in the surface snow of East Antarctica

Spatial trends of acetate (Ac−) and formate (Fo−) were determined in surface snow samples along a coastal-inland transect (180km) in the ice cap region at Princess Elizabeth Land and along a coastal transect in the Amery Ice Shelf (130km), East Antarctica. Variations in both Ac− and Fo− seem to be unrelated to the acidity of snow. Ionic balance determined for the snow samples indicate the availability of HNO3 that could undergo photolysis to produce hydroxyl radical (OH), one of the major reactants involved in oxidation reactions with organic matter. The strong positive correlations between Ac− and NO3− in snow from both regions indicate that NO3− mediated OH-oxidation of organic compounds in snow could be an important source of Ac− within the snowpack. On the other hand, negative correlation between Fo− and NO3− might indicate that sources other than OH-oxidation of organic matter may be dominant in the case of Fo−. Higher Ac− concentrations in the ice cap compared to the ice shelf correspond with long-range transport of biomass burning emissions to the ice cap region. Interaction of Ac− and Fo− with alkaline minerals could lead to their stability in the snowpack and minimize their loss from the snow surface. Resident microbial communities could also influence the budget of the carboxylic acids in snow.

Evolution process and sources of ambient volatile organic compounds during a severe haze event in Beijing, China

108 ambient volatile organic compounds (VOCs) were measured continuously at a time resolution of an hour using an online gas chromatography–frame ionization detector/mass spectrometry (GC–FID/MS) in October 2014 in Beijing, and positive matrix factorization (PMF) was performed with online data. The evolution process and causes for high levels of VOCs during a haze event were investigated through comprehensive analysis. Results show that mixing ratios of VOCs during the haze event (89.29 ppbv) were 2 to 5 times as that in non-haze days, There was a distinct accumulation process of VOCs at the beginning of the haze event, and the mixing ratios of VOCs maintained at the high levels until to the end of pollution when the mixing ratios of ambient VOCs recovered to the normal concentration levels in a few hours. Some reactive and toxic species increased remarkably as well, which indicates a potential health risk to the public in terms of VOCs. Eight sources were resolved by PMF, and results revealed gasoline exhaust was the largest contributor (32–46%) to the ambient VOCs in Beijing. Emissions of gasoline exhaust surged from 13.46 to 40.36 ppbv, with a similar variation pattern to total VOCs, indicating that high levels of VOCs were largely driven to by expanded vehicular emissions. Emissions of biomass burning also increased noticeably (from 2.32 to 11.12 ppbv), and backward trajectories analysis indicated regional transport of biomass burning emissions. Our findings suggested that extremely high levels of VOCs during the haze event was primarily attributed to vehicular emissions, biomass burning and regional transport, as well as stationary synoptic conditions.

Numerical Study of the Transport and Convective Mechanisms of Biomass Burning Haze in South-Southeast Asia

ABSTRACTThis study aims to identify the vertical transport mechanisms that uplifted the forest fire emissions from Sumatra to the upper troposphere during the June 2013 haze crisis. WRF-Chem is used to simulate the formation and transport of biomass-burning haze during the study period of 18th to 26th June 2013. The South-Southeast Asian synoptic weather patterns and their effects on the transport of biomass-burning emissions from Sumatra to Peninsular Malaysia were studied computationally to explain the phenomenon. Results show that PM10 emissions were lifted to 200 hPa height (approximately 12 km) over the Strait of Malacca on 24th June. The two identified vertical transport mechanisms confirmed a previously conjectured convergence over the Strait of Malacca and orographic lifting over Peninsular Malaysia. These mechanisms were able to uplift the biomass-burning emissions to the upper troposphere and this could have significant long-range transport and global climatic effects.

Biomass burning emissions contaminate winter snowfalls in urban Beijing: A case study in 2012

Three monosaccharide anhydrides levoglucosan, mannosan and galactosan were detected in winter snowfall samples of 2012 in urban Beijing. Concentrations of three isomers vary from 0.15 to 54.43ngmL−1, with an average value of 10.49ngmL−1. Levoglucosan is the most abundant component. Winter snowfalls are contaminated by biomass burning emissions seriously in urban Beijing. The main sources are softwood and crop residue burnings around Beijing from late autumn to early winter, while long-range transport of biomass burning emissions contribute more during the late winter. Concentrations of monosaccharide anhydrides in snowfall samples may be affected by both topography and the meteorological conditions around urban Beijing.

Importance of transboundary transport of biomass burning emissions to regional air quality in Southeast Asia during a high fire event

Abstract. Smoke from biomass and peat burning has a notable impact on ambient air quality and climate in the Southeast Asia (SEA) region. We modeled a large fire-induced haze episode in 2006 stemming mostly from Indonesia using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem). We focused on the evolution of the fire plume composition and its interaction with the urbanized area of the city state of Singapore, and on comparisons of modeled and measured aerosol and carbon monoxide (CO) concentrations. Two simulations were run with WRF-Chem using the complex volatility basis set (VBS) scheme to reproduce primary and secondary aerosol evolution and concentration. The first simulation referred to as WRF-FIRE included anthropogenic, biogenic and biomass burning emissions from the Global Fire Emissions Database (GFED3) while the second simulation referred to as WRF-NOFIRE was run without emissions from biomass burning. To test model performance, we used three independent data sets for comparison including airborne measurements of particulate matter (PM) with a diameter of 10 μm or less (PM10) in Singapore, CO measurements in Sumatra, and aerosol optical depth (AOD) column observations from four satellite-based sensors. We found reasonable agreement between the model runs and both ground-based measurements of CO and PM10. The comparison with AOD was less favorable and indicated the model underestimated AOD, although the degree of mismatch varied between different satellite data sets. During our study period, forest and peat fires in Sumatra were the main cause of enhanced aerosol concentrations from regional transport over Singapore. Analysis of the biomass burning plume showed high concentrations of primary organic aerosols (POA) with values up to 600 μg m−3 over the fire locations. The concentration of POA remained quite stable within the plume between the main burning region and Singapore while the secondary organic aerosol (SOA) concentration slightly increased. However, the absolute concentrations of SOA (up to 20 μg m−3) were much lower than those from POA, indicating a minor role of SOA in these biomass burning plumes. Our results show that about 21% of the total mass loading of ambient PM10 during the July–October study period in Singapore was due to biomass and peat burning in Sumatra, but this contribution increased during high burning periods. In total, our model results indicated that during 35 days aerosol concentrations in Singapore were above the threshold of 50 μg m−3 day−1 indicating poor air quality. During 17 days this was due to fires, based on the difference between the simulations with and without fires. Local pollution in combination with recirculation of air masses was probably the main cause of poor air quality during the other 18 days, although fires from Sumatra and probably also from Kalimantan (Indonesian part of the island of Borneo) added to the enhanced PM10 concentrations. The model versus measurement comparisons highlighted that for our study period and region the GFED3 biomass burning aerosol emissions were more in line with observations than found in other studies. This indicates that care should be taken when using AOD to constrain emissions or estimate ground-level air quality. This study also shows the need for relatively high resolution modeling to accurately reproduce the advection of air masses necessary to quantify the impacts and feedbacks on regional air quality.

WRF-Chem model estimates of equatorial Atlantic Ocean tropospheric ozone increases via June 2006 African biomass burning ozone precursor transport

Long-range horizontal and local vertical transport of biomass burning ozone precursors (i.e. carbon monoxide and nitrogen oxides) from Central Africa are simulated for June 2006. Twenty-kilometer resolution combined meteorological and chemical simulations examine transport pathways, spatial distribution, and quantities of ozone precursors and ozone. Results suggest that due to biomass burning, ozone mixing ratios increase by 28–33 parts per billion by volume in the lower troposphere (850 hecto-Pascals) over the Atlantic Ocean west of Central Africa during June. The inter-hemispheric transport of biomass burning emissions from Central Africa subsides over the Gulf of Guinea with a northward extent of approximately 2–5°N. In the lower troposphere, ozone mixing ratio increases decrease from 28 parts per billion by volume in the southern Gulf of Guinea to 2–3 parts per billion by volume on the Gulf of Guinea Coast. There is middle and upper tropospheric ozone enhancement of 6–12 parts per billion over the Equatorial Atlantic Ocean which is the result of convective detrainment of ozone precursors from deep convection on the Gulf of Guinea Coast followed by transport that propagates around a broad anticyclone. The model ozone produced by biomass burning emissions is less than the observed implying that lightning-induced nitrogen oxide emissions, which are not included in this simulation, are a significant tropospheric ozone source for the eastern Equatorial Atlantic Ocean.

Long-range transport of biomass burning emissions based on organic molecular markers and carbonaceous thermal distribution

Semi-continuous organic carbon (OC), elemental carbon (EC), and organic molecular markers were analyzed using the thermal optical transmittance method at the Gosan supersite (on Jeju Island, Korea), which has been widely used as a regional background site for East Asia. The Carbonaceous Thermal Distribution (CTD) method, which can provide detailed carbon signature characteristics relative to analytical temperature, was used to improve the carbon fractionation of the analytical method. Ground-based measurements were conducted from October 25 to November 5, 2010. During the sampling period, one high OC concentration event and two characteristic periods were observed. Considering the thermal distribution patterns, the relationship between the EC and black carbon (BC) by optical measurements, the backward trajectories, the aerosol optical thickness, the PM10 concentrations from the 316 PM-network sites that were operated by the Ministry of Environment in Korea, and the organic molecular markers, such as levoglucosan, PAHs, and organic acids, we concluded that the event was influenced by long-range transport from biomass burning emissions. This study discusses the CTD analysis with organic molecular marker concentrations, extracts and interprets additional carbon fractions from a semi-continuous data set, and provides knowledge regarding the origin of carbon sources and their behaviors.

Analysis of source regions for smoke events in Singapore for the 2009 El Nino burning season

As part of the 7 SouthEast Asian Studies (7SEAS) program, a solar radiation and chemistry sampling site (“supersite”) was developed at the National University of Singapore (NUS) to monitor regional air quality. The first intensive operations period for this site occurred between August and October 2009, a period that coincided with a moderate El Nino event and enhanced tropical burning, particularly in peatlands. We use data from this period to analyze the transport of biomass burning emissions in the Maritime Continent (MC) to the NUS supersite. An overview of the aerosol environment is provided for Singapore, followed by more detailed discussion of four aerosol events. The 2009 burning season was similar to those described in previous analyses, which showed that fire activity begins in the western half of the MC in Sumatra and propagates eastward in time. Similarly, agricultural burning occurs first, generally followed by deforestation and peatland fires. Some of the biomass burning emissions make their way into the free troposphere, where they are transported regionally by the prevailing wind patterns. Our analyses show that the seasonal winds at 850 hPa (∼1500 m) shift transport patterns from source regions to the southwest of Singapore, to regions to the southeast over the course of the summer monsoon, patterns that allow Singapore to be impacted by peak burning regions in the MC. In contrast, winds at the surface are more typically from the south and southeast, demonstrating the prevalence of vertical wind shear over the region. As a result of the variable source regions influencing different levels of the atmosphere over Singapore, in-situ surface observations of aerosol mass concentrations are not always consistent with inferences of the presence of enhanced aerosol concentration from column optical depth. Our findings confirm the complexity of aerosol sources and transport over the MC, and the key role that biomass burning emissions play in influencing column aerosol optical depth and total particulate mass concentrations at the surface. The sea-level altitude of the NUS supersite means that non-local pollution transported above the boundary layer cannot be reliably sampled and characterized, but the combined effects of local emissions and downward-mixed, non-local pollutants in Singapore were consistently measured.

Trends and variations in CO, C&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;H&amp;lt;sub&amp;gt;6&amp;lt;/sub&amp;gt;, and HCN in the Southern Hemisphere point to the declining anthropogenic emissions of CO and C&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;H&amp;lt;sub&amp;gt;6&amp;lt;/sub&amp;gt;

Abstract. We analyse the carbon monoxide (CO), ethane (C2H6) and hydrogen cyanide (HCN) partial columns (from the ground to 12 km) derived from measurements by ground-based solar Fourier Transform Spectroscopy at Lauder, New Zealand (45° S, 170° E), and at Arrival Heights, Antarctica (78° S, 167° E), from 1997 to 2009. Significant negative trends are calculated for all species at both locations, based on the daily-mean observed time series, namely CO (−0.94 ± 0.47% yr−1), C2H6 (−2.37 ± 1.18% yr−1) and HCN (−0.93 ± 0.47% yr−1) at Lauder and CO (−0.92 ± 0.46% yr−1), C2H6 (−2.82 ± 1.37% yr−1) and HCN (−1.41 ± 0.71% yr−1) at Arrival Heights. The uncertainties reflect the 95% confidence limits. However, the magnitudes of the trends are influenced by the anomaly associated with the 1997–1998 El Niño Southern Oscillation event at the beginning of the time series reported. We calculate trends for each month from 1997 to 2009 and find negative trends for all months. The largest monthly trends of CO and C2H6 at Lauder, and to a lesser degree at Arrival Heights, occur during austral spring during the Southern Hemisphere tropical and subtropical biomass burning period. For HCN, the largest monthly trends occur in July and August at Lauder and around November at Arrival Heights. The correlations between CO and C2H6 and between CO and HCN at Lauder in September to November, when the biomass burning maximizes, are significantly larger that those in other seasons. A tropospheric chemistry-climate model is used to simulate CO, C2H6, and HCN partial columns for the period of 1997–2009, using interannually varying biomass burning emissions from GFED3 and annually periodic but seasonally varying emissions from both biogenic and anthropogenic sources. The model-simulated partial columns of these species compare well with the measured partial columns and the model accurately reproduces seasonal cycles of all three species at both locations. However, while the model satisfactorily captures both the seasonality and trends in HCN, it is not able to reproduce the negative trends in either C2H6 or CO. A further simulation assuming a 35% decline of C2H6 and a 26% decline of CO emissions from the industrial sources from 1997 to 2009 largely captures the observed trends of C2H6 and CO partial columns at both locations. Here we attribute trends in HCN exclusively to changes in biomass burning and thereby isolate the influence of anthropogenic emissions as responsible for the long-term decline in CO and C2H6. This analysis shows that biomass burning emissions are the main factors in controlling the interannual and seasonal variations of these species. We also demonstrate contributions of biomass burning emission from different southern tropical and sub-tropical regions to seasonal and interannual variations of CO at Lauder; it shows that long-range transport of biomass burning emissions from southern Africa and South America have consistently larger year-to-year contributions to the background seasonality of CO at Lauder than those from other regions (e.g. Australia and South-East Asia). However, large interannual anomalies are triggered by variations in biomass burning emissions associated with large-scale El Niño Southern Oscillation and prolonged biomass burning events, e.g. the Australian bush fires.