Biomass Burning Episodes Research Articles

New particle formation in the presence of a strong biomass burning episode at a downwind rural site in PRD, China

ABSTRACTIn order to characterise the features of particle pollution in the Pearl River Delta (PRD) region, a 1-month intensive campaign was conducted at the rural supersite (Kaiping) in the autumn of 2008. In total, 12 new particle formation (NPF) events are identified out of 30 campaign days. The results show that in the case of higher source and sink values, the result of the competition between source and sink is more likely the key limiting factor to determine the observation of NPF events at Kaiping. One episode with consecutive NPF events in the presence of strong biomass burning plume was observed between 10 and 15 November. The elevation of particle volume concentration (6.1 µm3/cm3/day) is due to the coaction by the local biomass burning and secondary transformation. Organics and sulphates are the major components in PM1, accounting for 42 and 35% of the mass concentration, respectively. In this study, a rough estimation is applied to quantify the contributions of diverse sources to the particle number concentration. On average, the primary emission and secondary formation provide 28 and 72% of particle number concentration and 21 and 79% of mass concentration, respectively.

Chemical composition of PM2.5 in an urban environment in Chengdu, China: Importance of springtime dust storms and biomass burning

Daily PM2.5 samples were collected in Chengdu, a megacity in southwest China, for a period of one month in every season during 2009–2010. Mass concentrations of water-soluble inorganic ions, organic carbon (OC), elemental carbon (EC), levoglucosan (LG), water soluble organic carbon (WSOC), and elements were determined to identify the chemical characteristics and potential sources of PM2.5. The data obtained in spring were discussed in detail to explore the impacts of dust storms and biomass burning on the chemical aerosol properties. The daily PM2.5 mass concentrations ranged from 49.2 to 425.0μgm−3 with an annual average of 165.1±85.1μgm−3. The highest seasonal average of PM2.5 concentrations was observed in the winter (225.5±73.2μgm−3) and the lowest in the summer (113.5±39.3μgm−3). Dust storm influence was observed only during the spring, while biomass burning activities occurred frequently in late spring and early summer. In the spring season, water-soluble ions, total carbonaceous aerosols, and the sum of the dominant elements (Al, Si, Ca, Ti, Fe, Mn, Zn, Pb, and Cu) accounted for 30.0±9.3%, 38.6±11.4%, and 6.2±5.3%, respectively, of the total PM2.5 mass. Crustal element levels evidently increased during the dust storm episode and LG, OC, WSOC, Cl− and K+ concentrations increased by a factor of 2-7 during biomass burning episodes. Using the Positive Matrix Factorization (PMF) receptor model, four sources for spring aerosols were identified, including secondary sulfate and nitrate, motor vehicle emissions, soil dust, and biomass burning. The four sources were estimated to contribute 24.6%, 18.8%, 23.6% and 33.0%, respectively, to the total PM2.5 mass.

Physicochemical and toxicological characteristics of urban aerosols during a recent Indonesian biomass burning episode

Air particulate matter (PM) samples were collected in Singapore from 21 to 29 October 2010. During this time period, a severe regional smoke haze episode lasted for a few days (21-23 October). Physicochemical and toxicological characteristics of both haze and non-haze aerosols were evaluated. The average mass concentration of PM2.5 (PM with aerodynamic diameter of ≤2.5 μm) increased by a factor of 4 during the smoke haze period (107.2 μg/m(3)) as compared to that during the non-smoke haze period (27.0 μg/m(3)). The PM2.5 samples were analyzed for 16 priority polycyclic aromatic hydrocarbons (PAHs) listed by the United States Environmental Protection Agency and 10 transition metals. Out of the seven PAHs known as potential or suspected carcinogens, five were found in significantly higher levels in smoke haze aerosols as compared to those in the background air. Metal concentrations were also found to be higher in haze aerosols. Additionally, the toxicological profile of the PM2.5 samples was evaluated using a human epithelial lung cell line (A549). Cell viability and death counts were measured after a direct exposure of PM2.5 samples to A459 cells for a period of 48 h. The percentage of metabolically active cells decreased significantly following a direct exposure to PM samples collected during the haze period. To provide further insights into the toxicological characteristics of the aerosol particles, glutathione levels, as an indirect measure of oxidative stress and caspase-3/7 levels as a measure of apoptotic death, were also evaluated.

Evaluating the influences of biomass burning during 2006 BASE-ASIA: a regional chemical transport modeling

Abstract. To evaluate the impact of biomass burning from Southeast Asia to East Asia, this study conducted numerical simulations during NASA's 2006 Biomass-burning Aerosols in South-East Asia: Smoke Impact Assessment (BASE-ASIA). Two typical episode periods (27–28 March and 13–14 April) were examined. Two emission inventories, FLAMBE and GFED, were used in the simulations. The influences during two episodes in the source region (Southeast Asia) contributed to the surface CO, O3 and PM2.5 concentrations as high as 400 ppbv, 20 ppbv and 80 μg m−3, respectively. The perturbations with and without biomass burning of the above three species during the intense episodes were in the range of 10 to 60%, 10 to 20% and 30 to 70%, respectively. The impact due to long-range transport could spread over the southeastern parts of East Asia and could reach about 160 to 360 ppbv, 8 to 18 ppbv and 8 to 64 μg m−3 on CO, O3 and PM2.5, respectively; the percentage impact could reach 20 to 50% on CO, 10 to 30% on O3, and as high as 70% on PM2.5. In March, the impact of biomass burning mainly concentrated in Southeast Asia and southern China, while in April the impact becomes slightly broader and even could go up to the Yangtze River Delta region. Two cross-sections at 15° N and 20° N were used to compare the vertical flux of biomass burning. In the source region (Southeast Asia), CO, O3 and PM2.5 concentrations had a strong upward transport from surface to high altitudes. The eastward transport becomes strong from 2 to 8 km in the free troposphere. The subsidence process during the long-range transport contributed 60 to 70%, 20 to 50%, and 80% on CO, O3 and PM2.5, respectively to surface in the downwind area. The study reveals the significant impact of Southeastern Asia biomass burning on the air quality in both local and downwind areas, particularly during biomass burning episodes. This modeling study might provide constraints of lower limit. An additional study is underway for an active biomass burning year to obtain an upper limit and climate effects.

Attributing and quantifying carbon monoxide sources affecting the Eastern Mediterranean: a combined satellite, modelling, and synoptic analysis study

Abstract. Pollutants from global sources are known to affect the Eastern Mediterranean Shore (EMS). However, there has been no previous study explicitly locating the European sources, characterizing their transport pathways, and quantifying their contribution to local concentrations in the EMS. In the current study, spatially tagged carbon monoxide was used as a tracer for pollutant transport from Europe to the EMS over five consecutive years (2003–2007) using the global chemical transport model MOZART-4. The model results were compared against NOAA/GMD ground station data and remotely sensed data from the Terra/MOPITT satellite and found to agree well on monthly basis but do not agree on daily basis. On synoptic scale, there is agreement between MOZART and GMD during July to August. A budget analysis reveals the role of CO from hydrocarbon oxidation on CO concentration during summer. European anthropogenic emissions were found to significantly influence EM surface concentrations, while European biomass burning (BB) emissions were found to have only a small impact on EM surface concentrations. Over the five simulated years, only two European biomass burning episodes contributed more than 10 ppb to surface CO concentrations in the EM. CO enhancement in the EM during the summer was attributed to synoptic conditions prone to favorable transport from Turkey and Eastern Europe towards the EM rather than increased emissions. We attribute the apparently misleading association between CO emitted from European BB and CO enhancements over the EM to typical summer synoptic conditions caused by the lingering of an anticyclone positioned over the Western and Central Mediterranean Basin that lead to forest fires in the area. Combined with a barometric trough over the eastern part of the Mediterranean Basin, this generates a prevailing transport of air masses from Eastern Europe to the EMS. Synoptic scale variations are shown to change the transport pathways from Europe towards the EMS having an overall small affect. CO concentration over the EMS can be describe as having 3 components: the seasonal cycle, the cycle of CO produced from hydrocarbon oxidation and a synoptic variation.

Typical types and formation mechanisms of haze in an Eastern Asia megacity, Shanghai

Abstract. An intensive aerosol and gases campaign was performed at Shanghai in the Yangtze River Delta region over Eastern China from late March to early June 2009. This study provided a complementary picture of typical haze types and the formation mechanisms in megacities over China by using a synergy of ground-based monitoring, satellite and lidar observations. During the whole study period, several extreme low visibility periods were observed with distinct characteristics, and three typical haze types were identified, i.e. secondary inorganic pollution, dust, and biomass burning. Sulfate, nitrate and ammonium accounted for a major part of PM2.5 mass during the secondary inorganic pollution, and the good correlation between SO2/NOx/CO and PM2.5 indicated that coal burning and vehicle emission were the major sources. Large-scale regions with high AOD (aerosol optical depths) and low Ångström exponent were detected by remote-sensing observation during the dust pollution episode, and this episode corresponded to coarse particles rich in mineral components such as Al and Ca contributing 76.8% to TSP. The relatively low Ca/Al ratio of 0.75 along with the air mass backward trajectory analysis suggested the dust source was from Gobi Desert. Typical tracers for biomass burning from satellite observation (column CO and HCHO) and from ground measurement (CO, particulate K+, OC, and EC) were greatly enhanced during the biomass burning pollution episode. The exclusive linear correlation between CO and PM2.5 corroborated that organic aerosol dominated aerosol chemistry during biomass burning, and the high concentration and enrichment degree of arsenic (As) could be also partly derived from biomass burning. Aerosol optical profile observed by lidar demonstrated that aerosol was mainly constrained below the boundary layer and comprised of spheric aerosol (depolarization ratio <5%) during the secondary inorganic and biomass burning episodes, while thick dust layer distributed at altitudes from near surface to 1.4 km (average depolarization ratio = 0.122 ± 0.023) with dust accounting for 44–55% of the total aerosol extinction coefficient during the dust episode. This study portrayed a good picture of the typical haze types and proposed that identification of the complicated emission sources is important for the air quality improvement in megacities in China.

Influence of continental advection on aerosol characteristics over Bay of Bengal (BoB) in winter: results from W-ICARB cruise experiment

Abstract. The transport of aerosols and pollutants from continental India to the adjoining oceanic areas is a major topic of concern and several experimental campaigns have been conducted over the region focusing on aerosol characteristics and their climate implications. The present study analyzes the spectral aerosol optical depth (AOD) variations over Bay of Bengal (BoB) during Winter-Integrated Campaign for Aerosols, gases and Radiation Budget (W-ICARB) from 27 December 2008 to 30 January 2009 and investigates the influence of the adjoining landmass to the marine aerosol field. High AOD500 values (>0.7) occurred over northern BoB due to outflow of aerosols and pollutants from the densely populated Indo-Gangetic Plains (IGP); low AOD500 (0.1–0.2) was observed in central and southern BoB, far away from the mainland. The Angstrom exponent "α" was observed to be high (>1.2) near coastal waters, indicating relative abundance of accumulation-mode continental aerosols. On the other hand, over southern BoB its values dropped below ~0.7. National Center for Environmental Prediction (NCEP) reanalysis data on winds at 850 and 700 hPa, along with air-mass trajectories calculated using Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model, suggested transport of continental aerosols from central and northern India over the BoB. On the other hand, when the ship was crossing the eastern BoB, the aerosol loading was strongly affected by air-masses originating from Southeast Asia, causing an increase in AOD and α. Biomass-burning episodes over the region played an important role in the observed aerosol properties. Terra/Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) AOD550 and cruise measured AOD550 showed good agreement (R2 = 0.86 and 0.77, respectively) over BoB, exhibiting similar AOD and α spatio-temporal variation.

Variation in atmospheric aerosol properties over a tropical urban region associated with biomass-burning episodes – a study using satellite data and ground-based measurements

The change in aerosol properties and ground-reaching solar irradiance in different spectral bands associated with an intense biomass-burning episode has been examined in the present study. Synchronous ground-based measurements on aerosol optical depth (AOD), erythemal ultraviolet radiation (UVery), solar irradiance and light detecting and ranging (LIDAR) observations of aerosol backscatter were carried out in the urban region of Hyderabad, India. Air-mass back-trajectory analysis has been carried out to infer long-range transport of pollutants over the urban environment of Hyderabad. Ground-measured AOD showed ∼50% increase on 3 March 2009 compared to 2 March 2009, along with ∼13% and ∼31% increases in Angström's parameter (α) and turbidity coefficient (β). UVery and global solar irradiance showed ∼24% and ∼10% reduction, respectively, on a turbid day (3 March 2009) compared to a normal day (2 March 2009). The Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) AOD550 also showed higher values associated with long-range transport of aerosols from biomass burning over the region.

Characterization of aerosol optical depth, aerosol mass concentration, UV irradiance and black carbon aerosols over Indo-Gangetic plains, India, during fog period

Every year during winter months (December–January) fog formation over Indo-Gangetic plains (IGP) of Indian region is believed to create numerous hazards. The present study addresses variations in aerosol optical properties, aerosol mass concentration and their impact on solar irradiance for pre-during-post fog conditions of December 2004 over IGP, India. Continuous measurements on aerosol optical depth (AOD), total aerosol mass concentration, black carbon (BC) aerosols, UVery and UVA were carried out for pre, during and post fog periods over study site of Allahabad, India, during December 2004 as a part of Aerosol Land Campaign-II conducted by Indian Space Research Organization (ISRO). High aerosol mass concentrations were observed during fog and post-fog periods. Accumulation mode particle loading was found to be high during pre-fog period and coarse mode particle loading was observed to be high during fog and post-fog periods. Considerable reduction in UVery and UVA irradiance was observed during fog period compared with pre and post-fog periods. Analysis of NOAA-HYSPLIT model runs suggested that enhanced biomass burning episodes down-wind to the study area increased the concentration of AOD and BC.

Aerosol properties and associated radiative effects over Cairo (Egypt)

Cairo is one of the largest megacities in the World and the particle load of its atmosphere is known to be particularly important. In this work we aim at assessing the temporal variability of the aerosol's characteristics and the magnitude of its impacts on the transfer of solar radiation. For this we use the level 2 quality assured products obtained by inversion of the instantaneous AERONET sunphotometer measurements performed in Cairo during the Cairo Aerosol CHaracterization Experiment (CACHE), which lasted from the end of October 2004 to the end of March 2006. The analysis of the temporal variation of the aerosol's optical depth (AOD) and spectral dependence suggests that the aerosol is generally a mixture of at least 3 main components differing in composition and size. This is confirmed by the detailed analysis of the monthly-averaged size distributions and associated optical properties (single scattering albedo and asymmetry parameter). The components of the aerosol are found to be 1) a highly absorbing background aerosol produced by daily activities (traffic, industry), 2) an additional, ‘pollution’ component produced by the burning of agricultural wastes in the Nile delta, and 3) a coarse desert dust component. In July, an enhancement of the accumulation mode is observed due to the atmospheric stability favoring its building up and possibly to secondary aerosols being produced by active photochemistry. More generally, the time variability of the aerosol's characteristics is due to the combined effects of meteorological factors and seasonal production processes. Because of the large values of the AOD achieved during the desert dust and biomass burning episodes, the instantaneous aerosol radiative forcing (RF) at both the top (TOA) and bottom (BOA) of the atmosphere is maximal during these events. For instance, during the desert dust storm of April 8, 2005 RF BOA, RF TOA, and the corresponding atmospheric heating rate peaked at − 161.7 W/m 2, − 65.8 W/m 2, and 4.0 K/d, respectively. Outside these extreme events, the distributions of the radiative forcing values at BOA and TOA are Gaussian with means and standard deviations of − 58(± 27), and − 19(± 11)W/m 2, respectively. These two negative values indicate a cooling effect at the 2 atmospheric levels but the largest absolute value at BOA corresponds to a trapping of solar radiation inside the atmosphere. The averages of the instantaneous forcing efficiencies (FE) derived from measurements performed at solar zenith angles between 50 and 76° are − 195(± 42) and − 62(± 17)W/m 2.AOD 550 for BOA and TOA, respectively. The value at TOA is larger than in other urban environments, which could be due to the desert dust component backscattering more solar radiation to space than absorbing urban aerosols. The lower absorption of solar light by desert dust also explains qualitatively the lower than usual value of FE BOA. A more precise study of the effects of the desert dust and biomass burning aerosols shows that fluctuations of their monthly-averaged concentrations explain the departures of the TOA and BOA radiative forcings from the background situation. In April, the contributions of DD to the month averages of the instantaneous radiative forcing are as high as 53% at BOA, and 66% at TOA. In October, the biomass burning mode contributes 33 and 27% of these forcings, respectively. Noteworthy is that the contribution of DD to RF is never less than 17% (at BOA) and 27% (at TOA), emphasizing the importance of the mineral dust component on the transfer of solar radiation above Cairo, and this even in months when no major dust storm is observed.

Size distributions of dicarboxylic acids, ketoacids, α-dicarbonyls, sugars, WSOC, OC, EC and inorganic ions in atmospheric particles over Northern Japan: implication for long-range transport of Siberian biomass burning and East Asian polluted aerosols

Abstract. To better understand the size-segregated chemical composition of aged organic aerosols in the western North Pacific rim, day- and night-time aerosol samples were collected in Sapporo, Japan during summer 2005 using an Andersen impactor sampler with 5 size bins: Dp<1.1, 1.1–2.0, 2.0–3.3, 3.3–7.0, >7.0 μm. Samples were analyzed for the molecular composition of dicarboxylic acids, ketoacids, α-dicarbonyls, and sugars, together with water-soluble organic carbon (WSOC), organic carbon (OC), elemental carbon (EC) and inorganic ions. Based on the analyses of backward trajectories and chemical tracers, we found that during the campaign, air masses arrived from Siberia (a biomass burning source region) on 8–9 August, from China (an anthropogenic source region) on 9–10 August, and from the East China Sea/Sea of Japan (a mixed source receptor region) on 10–11 August. Most of the diacids, ketoacids, dicarbonyls, levoglucosan, WSOC, and inorganic ions (i.e., SO42−, NH4+ and K+) were enriched in fine particles (PM1.1) whereas Ca2+, Mg2+ and Cl− peaked in coarse sizes (>1.1 μm). Interestingly, OC, most sugar compounds and NO3− showed bimodal distributions in fine and coarse modes. In PM1.1, diacids in biomass burning-influenced aerosols transported from Siberia (mean: 252 ng m−3) were more abundant than those in the aerosols originating from China (209 ng m−3) and ocean (142 ng m−3), whereas SO42− concentrations were highest in the aerosols from China (mean: 3970 ng m−3) followed by marine- (2950 ng m−3) and biomass burning-influenced (1980 ng m−3) aerosols. Higher loadings of WSOC (2430 ng m−3) and OC (4360 ng m−3) were found in the fine mode, where biomass-burning products such as levoglucosan are abundant. This paper presents a case study of long-range transported aerosols illustrating that biomass burning episodes in the Siberian region have a significant influence on the chemical composition of carbonaceous aerosols in the western North Pacific rim.

Retrievals of aerosol single‐scattering albedo and effective aerosol layer height for biomass‐burning smoke: Synergy derived from “A‐Train” sensors

In this paper, we present results from a new algorithm which provides aerosol layer height (ALH) as well as single‐scattering albedo (SSA) for biomass‐burning smoke aerosols by merging measurements from three of the “A‐Train” satellite sensors: MODIS, OMI, and CALIOP. This algorithm has been applied successfully to biomass burning episodes over North America and Southeast Asia, and the corresponding SSA retrievals show good agreement with those from the AERONET. Furthermore, by combining ALH information from CALIOP with the retrieved SSA, extended information of ALH over wide areas can be obtained outside the CALIPSO track. Even when CALIPSO data are not available, this algorithm will still allow for the separation of aerosols residing within the boundary layer from those elevated in the free troposphere by combining only MODIS and OMI data. Results from this study will provide a better understanding of the height of smoke layers generated from biomass burning and thus improve aerosol models and the prediction of smoke aerosol transport.

Long-range transport episodes of fine particles in southern Finland during 1999–2007

The frequency, strength and sources of long-range transport (LRT) episodes of fine particles (PM 2.5) were studied in southern Finland using air quality monitoring results, backward air mass trajectories, remote sensing of fire hot spots, transport and dispersion modelling of smoke and chemical analysis of particle samples (black carbon, monosaccharide anhydrides, oxalate, succinate, malonate, SO 4 2−, NO 3 −, K + and NH 4 +). At an urban background site in Helsinki, the daily WHO guideline value (24-h PM 2.5 mean 25 μg m −3) was exceeded during 1–7 LRT episodes per year in 1999–2007. The 24-h mean maximum concentrations varied between 25 and 49 μg m −3 during the episodes, which was 3–6 times higher than the local mean concentration (8.7 μg m −3) in 1999–2007. The highest particle concentrations (max. 1-h mean 163 μg m −3) and the longest episodes (max. 9 days) were mainly caused by the emissions from open biomass burning, especially during springs and late-summers in 2002 and 2006. During the period 2001–2007, the satellite remote sensing of active fire hot spots and transport and dispersion modelling of smoke indicated that approximately half of the episodes were caused partly by the emissions from wildfires and/or agricultural waste burning in fields in Eastern Europe, especially in Russia, Belarus and Ukraine. Other episodes were mainly caused by the LRT of ordinary anthropogenic pollutants, e.g. from energy production, traffic, industry and wood combustion. During those ‘other episodes’, air masses also arrived from Eastern Europe, including Poland. The highest concentrations of biomass-burning tracers, such as monosaccharide anhydrides (levoglucosan + mannosan + galactosan) and K +, were observed during open biomass-burning episodes, but quite high values were also measured during some winter episodes due to wood combustion emissions. Our results indicate that open biomass burning in Eastern Europe causes high fine particle concentration peaks in large areas of Europe almost every year.

The synoptic and optical characteristics of the harmattan dust spells over Nigeria

The synoptic and optical characteristic of days during severe dust spells of December 1998, January 2000, February 2001, March 2003 and January 2005 at Ilorin (8°19′N, 4°20′E), Nigeria are investigated in this study. For example, during the severe dust storm of 5 January 2005 a strong synoptic-scale ridge developed which caused a shift in the position of the anticyclone over the desert region. These conditions led to a higher pressure gradient, and in turn resulted in the generation of dust at the 900 hPa level and wind speeds of up to ∼13 m/s over the source region between Bilma (18°12′N, 12°55′E), Faya Largeau (17°55′N, 19°07′E) and Maiduguri (11°50′N, 13°09′E) during the dust spells. Spectral aerosol optical depth τaλ, Angstrom parameters (α440-500 nm and β) derived from sunphotometer measurements and horizontal visibility (km) were used to study aerosol optical characteristics during and after the winter “harmattan” dust days. It was found that the daily mean τa500 nm during the dust episodes ranged between 0.31 and 3.28, with an average of 0.98 ± 0.50. τaλ showed a pronounced temporal trend, with maximum dust loading during intense dust haze as τa500 nm increased from a daily average value of 0.68 ± 0.48 to values >2.0 during severe dust spells. Daily mean spectral variations of the Angstrom exponent α show striking changes especially at high τaλ, when coarse mode aerosol dominate the accumulation mode aerosol. During the dust spells of 1998–2005 average horizontal visibility was reduced to as low as 1.66 ± 0.34 km at Ilorin with an increase in average τa500 nm and β to ∼2.06 ± 0.48 and 1.87 ± 0.49, respectively. However, for cases with strong biomass burning aerosol τa500 nm = 0.67 with α and β = 1.02 ± 0.08 and 0.31 ± 0.06, respectively. In some cases, smoke particles mix with desert dust to produce intermediate values of α. A trajectory analysis at three different levels (200, 500 and 1000 magl) during a severe dust and biomass burning episode were further used to explain the transport of aerosols to Ilorin, Nigeria.

Chemical composition of aerosols during a major biomass burning episode over northern Europe in spring 2006: Experimental and modelling assessments

The long-range transported smokes emitted by biomass burning had a strong impact on the PM 2.5 mass concentrations in Helsinki over the 12 days period in April and May 2006. To characterize aerosols during this period, the real-time measurements were done for PM 2.5, PM 2.5–10, common ions and black carbon. Moreover, the 24-h PM 1 filter samples were analysed for organic and elemental carbon (OC and EC), water-soluble organic carbon (WSOC), ions and levoglucosan. The Finnish emergency and air quality modelling system SILAM was used for the forecast of the PM 2.5 concentration generated by biomass burning. According to the real-time PM 2.5 data, the investigated period was divided into four types of PM situations: episode 1 (EPI-1; 25–29 April), episode 2 (EPI-2; 1–5 May), episode 3 (EPI-3; 5–6 May) and a reference period (REF; 24 March–24 April). EPI-3 included a local warehouse fire and therefore it is discussed separately. The PM 1 mass concentrations of biomass burning tracers—levoglucosan, potassium and oxalate—increased during the two long-range transport episodes (EPI-1 and EPI-2). The most substantial difference between the episodes was exhibited by the sulphate concentration, which was 4.9 (±1.4) μg m −3 in EPI-2 but only 2.4 (±0.31) μg m −3 in EPI-1 being close to that of REF (1.8±0.54 μg m −3). The concentration of particulate organic matter in PM 1 was clearly higher during EPI-1 (11±3.3 μg m −3) and EPI-2 (9.7±4.0 μg m −3) than REF (1.3±0.45 μg m −3). The long-range transported smoke had only a minor impact on the WSOC-to-OC ratio. According to the model simulations, MODIS detected the fires that caused the first set of concentration peaks (EPI-1) and the local warehouse fire (EPI-3), but missed the second one (EPI-2) probably due to dense frontal clouds.

Calmness of the aerosol layer in the atmosphere during biomass burning episodes

The aerosol optical depth (AOD) in the atmosphere has been retrieved from direct Sun (DS) measurements by the application of the Beer law (BL). On the other hand, the Langley method (LM), an offspring of the BL, is inappropriate to the retrieval of the AOD since it requires a stable atmosphere during DS measurements, a condition hardly achieved in typical turbulent scenes of biomass burning sites owing to the aerosol layer variability. In this work, some events of calmness of the aerosol layer during biomass burning episodes in the central area of Brazil are identified. Such a condition can be identified by low variability in the AOD values, and it makes the BL and the LM application yield similar results. Intervals of almost 2 hours have been identified, characterizing a state of calmness in the aerosol layer according to the chosen parameters. Measurement restrictions and statistical criteria for the retrieval of the AOD are used in the identification of the calmness states, and as a spin‐off the retrieval of the irradiance at the top of the atmosphere (the extrapolated value Ioλ) from the LM has been improved, reducing its uncertainty from 0.5988 × 107 to 0.1878 × 107 photons/s (p/s) at 306.3 nm and from 0.4002 × 107 to 0.1375 × 107 p/s at 320.1 nm. Consequently, the AOD uncertainty has also been reduced by 47 and 56%, respectively, on average.

Dust aerosols over India and adjacent continents retrieved using METEOSAT infrared radiance Part I: sources and regional distribution

Abstract. Mineral dust constitutes the single largest contributor to continental aerosols. To accurately assess the impact of dust aerosols on climate, the spatial and temporal distribution of dust radiative properties is essential. Regional characteristics of dust radiative properties, however, are poorly understood. The magnitude and even sign of dust radiative forcing is uncertain, as it depends on a number of parameters, such as vertical distribution of dust, cloud cover and albedo of the underlying surface. In this paper, infrared radiance (10.5-12.5 µm), acquired from the METEOSAT-5 satellite ( resolution), was used to retrieve regional characteristics of dust aerosols for all of 1999. The infrared radiance depression, due to the presence of dust in the atmosphere, has been used as an index of dust load, known as the Infrared Difference Dust Index (IDDI). There have been several studies in the past carried out over the Sahara using IDDI as a measure of dust load. Over the Indian region, however, studies on dust aerosols are sparse. Spatial and temporal variability in dust loading and its regional distribution over various arid and semiarid regions of India and adjacent continents (0-35° N; 30° E-100° E) (excluding Sahara) have been studied and the results are examined along with surface soil conditions (such as vegetation cover and soil moisture). The advantage of the IDDI method is that information on aerosol properties, such as chemical composition or microphysical properties, is not needed. A large day-to-day variation in IDDI was observed over the entire study region, with values ranging from 4 to 22 K. It was observed that dust activity starts by March over the Indian deserts, as well as over deserts of the Africa and Arabian regions. The IDDI reaches maximum during the period of May to August. Regional maps of IDDI, in conjunction with biomass burning episodes (using TERRA satellite fire pixel counts), suggest that large IDDI values observed during the winter months over Northern India could be due to a possible deposition of black carbon on larger dust aerosols. The IDDI values have been compared with another year (i.e. 2003), with a large number of dust storms reported by meteorological departments based on visibility data. During the dry season, the magnitude of the monthly average IDDI during 2003 was slightly higher than that of 1999. The monthly mean IDDI was in the range from 4 to 9 K over the Indian deserts, as well as over the deserts of Africa and Arabia. The maximum IDDI during a month was in the range from 6 to 18 K. Large IDDI values were observed even over vegetated regions (such as the vegetated part of Africa and central India), attributed to the presence of transported dust from nearby deserts.

Aerosol hygroscopic properties during Asian dust, pollution, and biomass burning episodes at Gosan, Korea in April 2001

Measurements of the aerosol hygroscopic growth factor, f(RH), and the physical and optical properties of aerosols were made at Gosan, Korea during the aerosol characterization experiment (ACE)-Asia 2001 field campaign (April 2001). The optical and hygroscopic properties of aerosols were characterized in terms of the air mass transport pathways. During the Asian dust period, σ sp and σ ap were remarkably elevated with mean and standard deviation of 238.6±55.3 Mm −1 and 24.2±10.9 Mm −1, respectively. The mean f(RH) for the pollution aerosols from Chinese sectors (2.75±0.38) in this study was much higher than that for the anthropogenic aerosols in Europe during ACE-2 (1.46±0.10) as well as that of the urban/industrial aerosols of the US east coast during TARFOX (1.81±0.37–2.30±0.24). The mean f(RH) during the smoke period (1.60±0.20) was comparable to that during INDOEX (1.58±0.21), and higher than that for SCAR-B in Brazil (1.16). We found a negative correlation ( r = 0.81 ) between f(RH) and OC concentration. This negative correlation suggests that organic aerosols have a strong influence on the smoke aerosol hygroscopicity.

Seasonal characteristics of biomass burning contribution to Beijing aerosol

110 atmospheric aerosol samples collected from November 1997 to October 1998 at two monitoring sites (Ming Tomb and Temple Heaven) in Beijing were analyzed for the concentration of organic carbon (OC) and water-soluble potassium (K+). Four biomass burning episodes, namely spring farming, summer harvesting, autumn harvesting and leaf falling were identified using the tracer of K+. Biomass burning contribution to the urban aerosol OC concentration in Beijing was estimated by regression analysis of OC and K+ concentration data. The slopes of regression analysis are similar at the two monitoring sites, presenting regional characteristics. Severe air pollution event occurred during autumn harvesting period in 1998 with substantial secondary OC formed, in which biomass burning was one of the major emission sources. Biomass burning is a prominent source of aerosol OC in Beijing and is featured by its seasonality and periodicity. It may contribute as much as 30 to 60 percent of the total OC in typical cases.

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 satellites.