Biomass Burning Period Research Articles

Functional group analysis by H NMR/chemical derivatization for the characterization of organic aerosol from the SMOCC field campaign

Abstract. Water soluble organic compounds (WSOC) in aerosol samples collected in the Amazon Basin in a period encompassing the middle/late dry season and the beginning of the wet season, were investigated by H NMR spectroscopy. HiVol filter samples (PM2.5 and PM>2.5) and size-segregated samples from multistage impactor were subjected to H NMR characterization. The H NMR methodology, recently developed for the analysis of organic aerosol samples, has been improved by exploiting chemical methylation of carboxylic groups with diazomethane, which allows the direct determination of the carboxylic acid content of WSOC. The content of carboxylic carbons for the different periods and sizes ranged from 12% to 20% of total measured carbon depending on the season and aerosol size, with higher contents for the fine particles in the transition and wet periods with respect to the dry period. A comprehensive picture is presented of WSOC functional groups in aerosol samples representative of the biomass burning period, as well as of transition and semi-clean atmospheric conditions. A difference in composition between fine (PM2.5) and coarse (PM>2.5) size fractions emerged from the NMR data, the former showing higher alkylic content, the latter being largely dominated by R-O-H (or R-O-R') functional groups. Very small particles (<0.14 μm), however, present higher alkyl-chain content and less oxygenated carbons than larger fine particles (0.42–1.2 μm). More limited variations were found between the average compositions in the different periods of the campaign.

Characterization of the organic composition of aerosols from Rondônia, Brazil, during the LBA-SMOCC 2002 experiment and its representation through model compounds

Abstract. The chemical composition of carbonaceous aerosols collected during the LBA-SMOCC field experiment, conducted in Rondônia, Brazil, in 2002 during the transition from the dry to the wet season, was investigated by a suite of state-of-the-art analytical techniques. The period of most intense biomass burning was characterized by high concentrations of submicron particles rich in carbonaceous material and water-soluble organic compounds (WSOC). At the onset of the rainy period, submicron total carbon (TC) concentrations decreased by about 20 times. In contrast, the concentration of supermicron TC was fairly constant throughout the experiment, pointing to a constant emission of coarse particles from the natural background. About 6–8% of TC (9–11% of WSOC) was speciated at the molecular level by GC-MS and liquid chromatography. Polyhydroxylated compounds, aliphatic and aromatic acids were the main classes of compounds accounted for by individual compound analysis. Functional group analysis by proton NMR and chromatographic separation on ion-exchange columns allowed characterization of ca. 50–90% of WSOC into broad chemical classes (neutral species/light acids/humic-like substances). In spite of the significant change in the chemical composition of tracer compounds from the dry to the wet period, the functional groups and the general chemical classes of WSOC changed only to a small extent. Model compounds representing size-resolved WSOC chemical composition for the different periods of the campaign are then proposed in this paper, based on the chemical characterization by both individual compound analysis and functional group analysis deployed during the LBA-SMOCC experiment. Model compounds reproduce quantitatively the average chemical structure of WSOC and can be used as best-guess surrogates in microphysical models involving organic aerosol particles over tropical areas affected by biomass burning.

Enhanced view of the “tropical Atlantic ozone paradox” and “zonal wave one” from the in situ MOZAIC and SHADOZ data

Ozone vertical profiles from the Measurements of Ozone from Airbus In‐service Aircraft (MOZAIC) program over Africa are used to complement pictures of the wave‐one pattern and the “tropical Atlantic paradox” identified through soundings in the Southern Hemisphere Additional Ozonesondes (SHADOZ) network. The Atlantic paradox refers to a greater tropospheric ozone column amount over the South Atlantic than the North Atlantic during the West African biomass burning season. SHADOZ and MOZAIC data from 1998–2002 and 1997–2004, respectively, are used to show that these two phenomena are linked. The combined data are used to address the following: Does the (continental) MOZAIC data modify the appearance of the paradox? Do lower tropospheric MOZAIC data lead to new conclusions about ozone in the wave‐one maximum region? During December, January, and February (DJF), the lower troposphere over Africa exhibits a higher ozone signal in the burning hemisphere, that is, north of the equator, so the “paradox” does not appear over the African continent. The MOZAIC data set over Africa highlights another component of the wave‐one feature when the tropospheric ozone mixing ratio is viewed in zonal cross section. The lower troposphere makes a nonnegligible contribution to the regionally higher ozone column during the biomass burning periods of each hemisphere (DJF) for West Africa and June, July, and August (JJA) for the central Africa region. A southern preference for the wave‐one character, previously deduced from satellite data, is confirmed with a stronger maximum in September, October, and November (SON). Both the paradox and wave‐one phenomena are consistent with a view that the African continent is a major source of biomass burning and lightning emissions.

Influence of Agricultural Biomass Burning on Aerosol Size Distribution and Dry Deposition in Southeastern Brazil

The size distributed composition of ambient aerosols is used to explore seasonal differences in particle chemistry and to show that dry deposition fluxes of soluble species, including important plant nutrients, increase during periods of biomass (sugar cane trash) burning in São Paulo State, Brazil. Measurements were made at a single site centrally located in the State's sugar cane growing region but away from the immediate vicinity of burns, so that the airsampled was representative of the regional background. Calculation of ion equivalent balances showed that during burning periods smaller particles (Aitken and accumulation modes) were more acidic, containing higher concentrations of SO4(2-), oxalate, NO3-, HCOO-, CH3COO-, and CI-, but insufficient NH4+ and K+ to achieve neutrality. Larger particles showed an anion deficit due to the presence of unmeasured ions and comprised resuspended dusts modified by accumulation of nitrate, chloride, and organic anions. Increases of resuspended particles during the burning season were attributed to release of earlier deposits from the surfaces of burning vegetation as well as increased vehicle movement on unsurfaced roads. During winter months the relative contribution of combined emissions from road transport and industry diminished due to increased emissions from biomass combustion and other activities specifically associated with the harvest period. Positive increments in annual particulate dry deposition fluxes due to higher fluxes during the sugar cane harvest were 44.3% (NH4+), 42.1% (K+), 31.8% (Mg2+), 30.4% (HCOO-), 12.8% (CI-), 6.6% (CH3COO-), 5.2% (Ca2+), 3.8% (SO4(2-)), and 2.3% (NO3-). Na+ and oxalate fluxes were seasonally invariant. Annual aerosol dry deposition fluxes (kg ha(-1)) were 0.5 (Na+), 0.25 (NH4+), 0.39 (K+), 0.51 (Mg2+), 3.19 (Ca2+), 1.34 (Cl-), 4.47 (NO3-), 3.59 (SO4(2-)), 0.58 (oxalate), 0.71 (HCOO-), and 1.38 (CH3COO-). Contributions of this mechanism to combined aerosol dry deposition and precipitation scavenging (inorganic species, excluding gaseous dry deposition) were 31% (Na+), 8% (NH4+), 26% (K+), 63% (Mg2+), 66% (Ca2+), 32% (Cl-), 33% (NO3-), and 36% (SO4(2-)).

Chemical Composition of Post-Harvest Biomass Burning Aerosols in Gwangju, Korea

The main objective of this study was to investigate the chemical characteristics of post-harvest biomass burning aerosols from field burning of barley straw in late spring and rice straw in late fall in rural areas of Korea. A 12-hr integrated intensive sampling of particulate matter (PM) with an aerodynamic diameter less than or equal to 10 μm (PM10) and PM with an aerodynamic diameter less than or equal to 2.5 μm (PM25) biomass burning aerosols had been conducted continuously in Gwangju, Korea, during two biomass burning periods: June 4–15, 2001, and October 8–November 14, 2002. The fine and coarse particles of biomass burning aerosols were analyzed for mass and ionic, elemental, and carbonaceous species. The average fine and coarse mass concentrations of biomass burning aerosols were, respectively, 129.6 and 24.2 μg/m3 in June 2001 and 47.1 and 33.2 μg/m3 in October–November 2002. An exceptionally high PM2.5 concentration of 157.8 μg/m3 was observed during biomass burning events under stagnant atmospheric conditions. In the fine mode, chlorine and potassium were unusually rich because of the high content of semi-arid vegetation. Both organic carbon (OC) and elemental carbon increased during the bio-mass burning periods, with the former exhibiting a higher abundance. PM from the open field burning of agricultural waste has an adverse impact on local air quality and regional climate.

Impact of biomass burning aerosols on UV erythema—a case study from northeast region of India

Total spectral solar irradiance and biologically active solar ultraviolet radiation (UV ery, 280– 315 nm ) have been monitored during biomass burning period of moist deciduous forests in the Northeastern India. Aerosol optical depth values varied from 0.5 to 4.2 during different stages of burning. Total solar irradiance measurements suggested decrease in direct solar irradiance during burning with increase in diffused radiation. A statistical fit of AOD (500 nm) through UV ery shows negative gradient and for every 0.1 increase in aerosol optical depth during biomass burning period 0.01 W m −2 reduction in the ground reaching UV ery has been observed.

Analysis of tropospheric NOx over Asia using the model of atmospheric transport and chemistry (MATCH-MPIC) and GOME-satellite observations

Abstract The distribution and budget of tropospheric NOx over Asia, especially India, are examined using the global 3D chemistry–meteorology model MATCH-MPIC and GOME NO2 columns. Enhanced abundances of NO2 over China and northeast India are reproduced by the model, as are the pronounced maxima during biomass burning periods, though somewhat underestimated. The mean NO2 column over India is also reproduced, though the model has trouble with the seasonal cycle for unknown reasons. Model sensitivity tests for the Indian region indicate that the scaled sensitivity to changes in the local NOx source is 60–70% for lower tropospheric NOx and is only 10–25% for tropospheric O3, indicating that moderate reductions or increases in current NOx emissions are not expected to lead to large changes in regional O3 levels. In the upper troposphere, during winter nearly all of the NOx comes from remote sources, while in summer deep convection causes the upper troposphere to become sensitive to local surface emissions (∼40–50% scaled sensitivity) and lightning NOx production (∼10–20%). The regional lifetime of NOx estimated for India, based on MATCH output is about 15–23 h, comparable to the lifetime of NOx over China (14–21 h), while over Indonesia (23–43 h) and North Asia (21–47 h), it is longer and highly seasonal. Implications of these results are discussed.

Characterization of aerosols from biomass burning––a case study from Mizoram (Northeast), India

Physical and optical properties of biomass burning aerosols in Northeastern region, India analyzed based on measurements made during February 2002. Large spatial extent of Northeastern Region moist tropical to moist sub-tropical forests in India have high frequency of burning in annual dry seasons. Characterization of resultant trace gases and aerosols from biomass burning is important for the atmospheric radiative processes. Aerosol optical depth (AOD) observed to be high during burning period compared to pre- and post-burning days. Peak period of biomass burning is highly correlated with measured AOD and total columnar water vapor. Size distribution of aerosols showed bimodal size distribution during burning day and unimodal size distribution during pre- and post-burning days. Size distribution retrievals from biomass burning aerosols show dominance of accumulation mode particles. Weighted mean radius is high (0.22 μm) during burning period. Columnar content of aerosols observed to be high during burning period in addition to the drastic reduction of visibility. During the burning day Anderson sampler measurements showed dominance of accumulation mode particles. The diurnal averaged values of surface shortwave aerosol radiative forcing of biomass burning aerosols varies from −59 to −87 W m −2 on different days. Measured and modeled solar irradiances are also discussed in the paper.

Refractive index of aerosol particles over the Amazon tropical forest during LBA-EUSTACH 1999

Optical properties of aerosol particles were characterized during two field campaigns at a remote rainforest site in Rondônia, Brazil, as part of the project European Studies on Trace Gases and Atmospheric Chemistry, a contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). The measurements included background (wet season), biomass burning (dry season), and transition period conditions. Optical measurements of light scattering and absorption were combined with data on number/size distributions in a new iterative method, which retrieves the effective imaginary refractive index of the particles at a wavelength of 545 nm . For ambient relative humidities lower than 80%, background aerosols exhibited an average refractive index of 1.42−0.006 i. Biomass burning aerosols displayed a much larger imaginary part, with an average refractive index of 1.41−0.013 i. Other climate-relevant parameters were estimated from Mie calculations. These include single-scattering albedos of 0.93±0.03 and 0.90±0.03 (at ambient humidity), asymmetry parameters of 0.63±0.02 and 0.70±0.03, and backscatter ratios of 0.12±0.01 and 0.08±0.01 for background and biomass burning aerosols, respectively.

Multiyear infrared solar spectroscopic measurements of HCN, CO, C2H6, and C2H2tropospheric columns above Lauder, New Zealand (45°S latitude)

Near‐simultaneous, 0.0035 or 0.007 cm−1resolution infrared solar absorption spectra of tropospheric HCN, C2H2, CO, and C2H6have been recorded from the Network for the Detection of Stratospheric Change station in Lauder, New Zealand (45.04°S, 169.68°E, 0.37 km altitude). All four molecules were measured on over 350 days with HCN and C2H2reported for the first time based on a new analysis procedure that significantly increases the effective signal‐to‐noise of weak tropospheric absorption features in the measured spectra. The CO measurements extend by 2.5 years a database of measurements begun in January 1994 for CO with improved sensitivity in the lower and middle troposphere. The C2H6measurements lengthen a time series begun in July 1993 with peak sensitivity in the upper troposphere. Retrievals of all four molecules were obtained with an algorithm based on the semiempirical application of the Rodgers optimal estimation technique. Columns are reported for the 0.37‐ to 12‐km‐altitude region, approximately the troposphere above the station. The seasonal cycles of all four molecules are asymmetric, with minima in March–June and sharp peaks and increased variability during August–November, which corresponds to the period of maximum biomass burning near the end of the Southern Hemisphere tropical dry season. Except for a possible HCN column decrease, no evidence was found for a statistically significant long‐term trend.

Ozone generation over the Indian Ocean during the South African biomass-burning period: case study of October 1992.

Abstract. In this study, we present an estimation of photochemical ozone production during free tropospheric transport between the African biomass burning area and Reunion Island (Indian Ocean) by means of trajectory-chemistry model calculations. Indeed, enhanced ozone concentrations (80–100 ppbv) between 5 and 8 km height over Reunion Island are encountered during September–October when African biomass burning is active. The measurements performed during flight 10 of the TRACE-A campaign (October 6, 1992) have been used to initialise the lagrangian trajectory-chemistry model and several chemical forward trajectories, which reach the area of Reunion Island some days later, are calculated. We show that the ozone burden already present in the middle and upper troposphere over Southern Africa, formed from biomass burning emissions, is further enhanced by photochemical production over the Indian Ocean at the rate of 2.5 - 3 ppbv/day. The paper presents sensitivity studies of how these photochemical ozone production rates depend on initial conditions. The rates are also compared to those obtained by other studies over the Atlantic Ocean. The importance of our results for the regional ozone budget over the Indian Ocean is briefly discussed.Key words. Atmospheric composition and structure (evolution of the atmosphere; troposphere – composition and chemistry); meterorology and atmospheric dynamics (tropical meteorology)

A revised high-resolution oxygen-isotope chronology for ODP-668B: implications for Quaternary biomass burning in Africa

We present a high-resolution oxygen-isotope chronology to Stage 13 for core ODP-668B, Sierra Leone Rise, east equatorial Atlantic. Observed variations in the abundance of oxidation resistant elemental carbon (OREC) in this core are reinterpreted in the light of this revised chronology, which differs significantly from that proposed by Bird and Cali [Nature 394 (1998) 767]. Peaks in OREC abundance are considered to be related to periods of intense biomass burning in adjacent areas of sub-Saharan Africa during periods of rapid climate change. OREC peaks do not occur during peak glacial times possibly due to low fuel loads and generally cool/dry climate. The most recent OREC peak in the current interglacial period is not unique, as a peak of similar intensity occurs at the peak of the Stage 7 interglacial. Therefore, an anthropogenic origin for the most recent peak cannot be unequivocally established.

Characterization of the optical properties of biomass burning aerosols in Zambia during the 1997 ZIBBEE field campaign

The physical and optical properties of biomass burning aerosols in a savanna region in south central Africa (Zambia) were analyzed from measurements made during the Zambian International Biomass Burning Emissions Experiment (ZIBBEE) during August‐September 1997. Due to the large spatial extent of African savannas and the high frequency of occurrence of burning in the annual dry seasons, characterization of the optical properties of the resultant biomass burning aerosols is important for the study of atmospheric radiative processes and for remote sensing of both surface and atmospheric properties in these regions. Aerosol Robotic Network Sun‐sky radiometer spectral measurements of direct Sun observations and directional sky radiances were utilized to infer spectral aerosol optical depths (τa), aerosol size distributions, and single‐scattering albedos. During the primary ZIBBEE study period, which coincided with the peak period of biomass burning in the region, there was a high correlation between the measured τaand the total column water vapor or precipitable water vapor (PWV), suggesting transport of smoke aerosol from regions with higher PWV. Size distribution retrievals of the biomass burning smoke show that the accumulation mode dominated and a comparison with smoke from Amazonia (Bolivia) shows a shift toward smaller particles for African savanna smoke. This may be the result of differences in mode of combustion (flaming versus smoldering), fuel type and moisture content, and the aging processes of the aerosol. The single‐scattering albedo (ω0) of the aerosols were retrieved using several approaches, yielding average values of ω0at ∼550 nm during ZIBBEE varying from ∼0.82 to ∼0.85, thus showing good agreement within the retrieval uncertainty of ∼0.03 of these methods. In general, ω0was relatively constant as a function of aerosol loading, with very little change occurring for τaat 440 nm ranging from 0.7 to 1.7. African savanna smoke exhibits significantly higher absorption than smoke from Amazonian forested regions and also a greater rate of decrease of ω0with increasing wavelength. Variations in the spectral change of the Angström wavelength exponent were also investigated with respect to the degree of aerosol absorption and changes in the accumulation mode size distributions.

Modeling of gaseous, aerosol, and cloudiness effects on surface solar irradiance measured in Brazil's Amazonia 1992–1995

The effects of water vapor, aerosol, and cloudiness on the incident surface solar irradiance continuously measured in Brazil's Amazonia at six observational sites from 1992 to 1995 are examined by means of a clear‐sky broadband radiative transfer model. The aerosol optical depth and precipitable water, both retrieved from Sun photometer measurements, serve as inputs to the model. Computed monthly mean values of clear‐sky surface irradiance are analyzed in conjunction with the monthly mean values of all‐sky surface irradiance measured on the ground. To assess the effect of cloudiness, we present the cloud radiative forcing and cloud radiative forcing ratio at the surface, both widely employed in cloud radiation budget studies. By its definition the monthly mean cloud radiative forcing (cloud radiative forcing ratio) is the difference (ratio) between surface solar irradiances under all‐sky and clear‐sky conditions. The analysis of the irradiances, as computed and as measured, shows that during the wet season the gaseous and cloudiness effects on the solar radiation attenuation in the atmosphere are comparable, while the aerosol influence is much smaller. The aerosol effect increases and cloudiness effect decreases in the second half of the dry season. Thus during the biomass burning period in southern Amazonia, the water vapor and aerosol effects become comparable, while the cloudiness impact is 2–3 times smaller. Both cloudiness and aerosol effects have strong seasonal variations, while the gaseous effect changes slightly throughout the year.

Impact of biomass burning on rainwater acidity and composition in Singapore

The Indonesian forest fires that took place from August through October 1997 released large amounts of gaseous and particulate pollutants into the atmosphere. The particulate emissions produced a plume that was easily visible by satellite and significantly affected regional air quality in Southeast Asia. This prolonged haze episode provided an unprecedented opportunity to examine the effects of biomass burning on regional atmospheric chemistry. We undertook a comprehensive field study to assess the influence of biomass burning impacted air masses on precipitation chemistry in Singapore. Major inorganic and organic ions were determined in 104 rain samples collected using an automated wet‐only sampler from July through December 1997. Mean pH values ranged from 3.79 to 6.20 with a volume‐weighted mean of 4.35. There was a substantially large number of rain events with elevated concentrations of these ions during the biomass burning period. The relatively high concentrations of SO2−4, NO−3, and NH+4 observed during the burning period are attributed to a long residence time of air masses, leading to progressive gas to particle conversion of biomass burning emission components. The decrease in pH of precipitation in response to the increased concentrations of acids is only marginal, which is ascribed to neutralization of acidity by NH3 and CaCO3.

The vertical distribution of ozone measured at Brazzaville, Congo during TRACE A

The distribution of ozone in the African tropical region is examined for measurements made between late June 1990 and early October 1992 in support of the NASA Global Tropospheric Experiment/Transport and Atmospheric Chemistry Near the Equator‐Atlantic (GTE/TRACE A) experiment conducted at Brazzaville (4°17′S, 15°15′E;) in September and October 1992. A set of ozone data has been obtained in the troposphere and the stratosphere to above 30 km using balloon‐borne electrochemical concentration cell ozonesondes. The analysis of the tropospheric data confirms the seasonal trends of ozone in these latitudes, which shows, in particular, the presence of an ozone‐enriched layer located between 1‐ and 4‐km altitude during the dry season of each hemisphere. A more detailed analysis of the data set for September–October 1992 shows a behavior of ozone which suggests the presence of two periods of biomass burning in the dry season of the southern hemisphere. In addition, this study shows that the dry season of the northern hemisphere has a limited influence on tropospheric ozone at large distances.

Chemical composition of acid rains in the Venezuelan savannah region

The chemical composition of rain events has been determined at 6 sites in the Venezuelan savannah region. The results indicate that precipitations are little affected by anthropogenic emissions and that rain concentrations of anions and cations are similar to those observed at “remote” continental sites. At each location, the rain is acidic with average pHs ranging from 4.4 to 5.4. Over 50% of the free acidity may be due to formic and acetic acids. HNO3 and H2SO4 contribute only less than 36%. NH3 plays a significant role as neutralizing compound; Ca and Mg carbonates may also, in some cases, reduce the acidity of the rain solution. A complete evaluation of the ions that take part in the acid-base equilibrium is given. The participation of organic acid is discussed in detail. The first rains of the season, during biomass burning periods, are heavily loaded with several compounds, showing that emissions and/or atmospheric production are enhanced during vegetation fires. No significant variation in rain acidity was observed; it is likely that the larger atmospheric photochemical formation of organic and inorganic acids during burning is neutralized by a large primary emission of NH3. The study of these “particular” rains is useful in searching for pollutants emitted by fires and/or possible atmospheric processes that may occur in the associated haze layer.