Transport Of Biomass Burning Emissions Research Articles

Impact of a monotonic advection scheme with low numerical diffusion on transport modeling of emissions from biomass burning

An advection scheme, which maintains the initial monotonic characteristics of a tracer field being transported and at the same time produces low numerical diffusion, is implemented in the Coupled Chemistry‐Aerosol‐Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CCATT‐BRAMS). Several comparisons of transport modeling using the new and original (non‐monotonic) CCATT‐BRAMS formulations are performed. Idealized 2‐D non‐divergent or divergent and stationary or time‐dependent wind fields are used to transport sharply localized tracer distributions, as well as to verify if an existent correlation of the mass mixing ratios of two interrelated tracers is kept during the transport simulation. Further comparisons are performed using realistic 3‐D wind fields. We then perform full simulations of real cases using data assimilation and complete atmospheric physics. In these simulations, we address the impacts of both advection schemes on the transport of biomass burning emissions and the formation of secondary species from non‐linear chemical reactions of precursors. The results show that the new scheme produces much more realistic transport patterns, without generating spurious oscillations and under‐ and overshoots or spreading mass away from the local peaks. Increasing the numerical diffusion in the original scheme in order to remove the spurious oscillations and maintain the monotonicity of the transported field causes excessive smoothing in the tracer distribution, reducing the local gradients and maximum values and unrealistically spreading mass away from the local peaks. As a result, huge differences (hundreds of %) for relatively inert tracers (like carbon monoxide) are found in the smoke plume cores. In terms of the secondary chemical species formed by non‐linear reactions (like ozone), we found differences of up to 50% in our simulations.

Cloud condensation nuclei as a modulator of ice processes in Arctic mixed-phase clouds

Abstract. We propose that cloud condensation nuclei (CCN) concentrations are important for modulating ice formation of Arctic mixed-phase clouds, through modification of the droplet size distribution. Aircraft observations from the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) study in northern Alaska in April 2008 allow for identification and characterization of both aerosol and trace gas pollutants, which are then compared with cloud microphysical properties. Consistent with previous studies, we find that the concentration of precipitating ice particles (>400 μm) is correlated with the concentration of large droplets (>30 μm). We are further able to link the observed microphysical conditions to aerosol pollution, originating mainly from long range transport of biomass burning emissions. The case studies demonstrate that polluted mixed-phase clouds have narrower droplet size distributions and contain 1–2 orders of magnitude fewer precipitating ice particles than clean clouds at the same temperature. This suggests an aerosol indirect effect leading to greater cloud lifetime, greater cloud emissivity, and reduced precipitation. This result is opposite to the glaciation indirect effect, whereby polluted clouds are expected to precipitate more readily due to an increase in the concentration of particles acting as ice nuclei.

Trans-Pacific and Regional Atmospheric Transport of Polycyclic Aromatic Hydrocarbons and Pesticides in Biomass Burning Emissions to Western North America

The trans-Pacific and regional North American atmospheric transport of polycyclic aromatic hydrocarbons (PAHs) and pesticides in biomass burning emissions was measured in air masses from April to September 2003 at two remote sites in western North America. Mary's Peak Observatory (MPO) is located in Oregon's Coast Range and Cheeka Peak Observatory (CPO) is located on the tip of the Olympic Peninsula in Washington State. During this time period, both remote sites were influenced by PAH and pesticide emissions from forest fires in Siberia and regional fires in Oregon and Washington State. Concurrent samples were taken at both sites on June 2 and August 4, 2003. On these dates, CPO had elevated gas phase PAH, alpha-hexachlorocyclohexane, and retene concentrations (p < 0.05) and MPO had elevated retene, particulate phase PAH, and levoglucosan concentrations due to trans-Pacific transport of emissions from fires in Siberia. In addition, during the April to September 2003 sampling period, CPO and MPO were influenced by emissions from regional fires that resulted in elevated levoglucosan, dacthal, endosulfan, and gas phase PAH concentrations. Burned and unburned forest soil samples collected from the regional forest fire area showed that 34-100% of the pesticide mass was lost from soil due to burning. These data suggest that the trans-Pacific and regional atmospheric transport of biomass burning emissions results in elevated PAH and pesticide concentrations in western North America. The elevated pesticide concentrations are likely due to re-emission of historically deposited pesticides from the soil and vegetation during the fire event.

Biomass burning in Siberia and Kazakhstan as an important source for haze over the Alaskan Arctic in April 2008

During the ARCPAC (Aerosol, Radiation, and Cloud Processes affecting Arctic Climate) airborne field experiment in April 2008 in northern Alaska, about 50 plumes were encountered with the NOAA WP‐3 aircraft between the surface and 6.5 km. Onboard measurements and the transport model FLEXPART showed that most of the plumes were emitted by forest fires in southern Siberia‐Lake Baikal area and by agricultural burning in Kazakhstan‐southern Russia. Unexpectedly, these biomass burning plumes were the dominant aerosol and gas‐phase features encountered in this area during April. The influence on the plumes from sources other than burning was small. The chemical characteristics of plumes from the two source regions were different, with higher enhancements relative to CO for most gas and aerosol species from the agricultural fires. In 2008, the fire season started earlier than usual in Siberia, which may have resulted in unusually efficient transport of biomass burning emissions into the Arctic.

Record high peaks in PCB concentrations in the Arctic atmosphere due to long-range transport of biomass burning emissions

Abstract. Soils and forests in the boreal region of the Northern Hemisphere are recognised as having a large capacity for storing air-borne Persistent Organic Pollutants (POPs), such as the polychlorinated biphenyls (PCBs). Following reductions of primary emissions of various legacy POPs, there is an increasing interest and debate about the relative importance of secondary re-emissions on the atmospheric levels of POPs. In spring of 2006, biomass burning emissions from agricultural fires in Eastern Europe were transported to the Zeppelin station on Svalbard, where record-high levels of many air pollutants were recorded (Stohl et al., 2007). Here we report on the extremely high concentrations of PCBs that were also measured during this period. 21 out of 32 PCB congeners were enhanced by more than two standard deviations above the long-term mean concentrations. In July 2004, about 5.8 million hectare of boreal forest burned in North America, emitting a pollution plume which reached the Zeppelin station after a travel time of 3–4 weeks (Stohl et al., 2006). Again, 12 PCB congeners were elevated above the long-term mean by more than two standard deviations, with the less chlorinated congeners being most strongly affected. We propose that these abnormally high concentrations were caused by biomass burning emissions. Based on enhancement ratios with carbon monoxide and known emissions factors for this species, we estimate that 130 and 66 μg PCBs were released per kilogram dry matter burned, respectively. To our knowledge, this is the first study relating atmospheric PCB enhancements with biomass burning. The strong effects on observed concentrations far away from the sources, suggest that biomass burning is an important source of PCBs for the atmosphere.

Satellite‐observed pollution from Southern Hemisphere biomass burning

Biomass burning is a major source of pollution in the tropical Southern Hemisphere, and fine mode carbonaceous particles are produced by the same combustion processes that emit carbon monoxide (CO). In this paper we examine these emissions with data from the Terra satellite, CO profiles from the Measurement of Pollution in the Troposphere (MOPITT) instrument, and fine‐mode aerosol optical depth (AOD) from the Moderate‐Resolution Imaging Spectroradiometer (MODIS). The satellite measurements are used in conjunction with calculations from the MOZART chemical transport model to examine the 2003 Southern Hemisphere burning season with particular emphasis on the months of peak fire activity in September and October. Pollutant emissions follow the occurrence of dry season fires, and the temporal variation and spatial distributions of MOPITT CO and MODIS AOD are similar. We examine the outflow from Africa and South America with emphasis on the impact of these emissions on clean remote regions. We present comparisons of MOPITT observations and ground‐based interferometer data from Lauder, New Zealand, which indicate that intercontinental transport of biomass burning pollution from Africa often determines the local air quality. The correlation between enhancements of AOD and CO column for distinct biomass burning plumes is very good with correlation coefficients greater than 0.8. We present a method using MOPITT and MODIS data for estimating the emission ratio of aerosol number density to CO concentration which could prove useful as input to modeling studies. We also investigate decay of plumes from African fires following export into the Indian Ocean and compare the MOPITT and MODIS measurements as a way of estimating the regional aerosol lifetime. Vertical transport of biomass burning emissions is also examined using CO profile information. Low‐altitude concentrations are very high close to source regions, but further downwind of the continents, vertical mixing takes place and results in more even CO vertical distributions. In regions of significant convection, particularly in the equatorial Indian Ocean, the CO mixing ratio is greater at higher altitudes, indicating vertical transport of biomass burning emissions to the upper troposphere.

Monitoring the transport of biomass burning emissions in South America

The atmospheric transport of biomass burning emissions in the South American and African continents is being monitored annually using a numerical simulation of air mass motions; we use a tracer transport capability developed within RAMS (Regional Atmospheric Modeling System) coupled to an emission model. Mass conservation equations are solved for carbon monoxide (CO) and particulate material (PM2.5). Source emissions of trace gases and particles associated with biomass burning activities in tropical forest, savanna and pasture have been parameterized and introduced into the model. The sources are distributed spatially and temporally and assimilated daily using the biomass burning locations detected by remote sensing. Advection effects (at grid scale) and turbulent transport (at sub-grid scale) are provided by the RAMS parameterizations. A sub-grid transport parameterization associated with moist deep and shallow convection, not explicitly resolved by the model due to its low spatial resolution, has also been introduced. Sinks associated with the process of wet and dry removal of aerosol particles and chemical transformation of gases are parameterized and introduced in the mass conservation equation. An operational system has been implemented which produces daily 48-h numerical simulations (including 24-h forecasts) of CO and PM2.5, in addition to traditional meteorological fields. The good prediction skills of the model are demonstrated by comparisons with time series of PM2.5 measured at the surface.

Regional and hemispheric impacts of anthropogenic and biomass burning emissions on summertime CO and O3 in the North Atlantic lower free troposphere

We report summertime measurements of CO and O3 obtained during 2001–2003 at the PICO‐NARE mountaintop station in the Azores. Frequent events of elevated CO mixing ratios were observed. On the basis of backward trajectories arriving in the free troposphere and global simulations of biomass burning plumes, we attribute nearly all these events to North American pollution outflow and long‐range transport of biomass burning emissions. There was a high degree of interannual variability in CO levels: median [CO] ranged from 65 ppbv in 2001 to 104 ppbv in 2003. The highest concentrations were associated with transport of Siberian fire emissions during summer 2003, when Siberian fire activity was unusually high. Ozone mixing ratios also increased (by up to ∼30 ppbv) during the fire events. These findings demonstrate the significant hemispheric scale impact that biomass burning events have on background CO and O3 levels. O3 enhancements of similar magnitude were also observed in North American pollution outflow. O3 and CO were correlated during North American outflow events, with a slope averaging 1.0 (d[O3]/d[CO], ppbv/ppbv) when no fire impact was present. This slope is more than 80% larger than early 1990s observations made in the eastern United States and nearshore outflow region, even after accounting for declining U.S. CO emissions and for CO loss during transport to the Azores, and is not consistent with simple dilution of U.S. outflow with marine background air. We conclude that a significantly larger amount of O3 production occurred in the air sampled during this study, and we suggest several potential reasons for this, each of which could imply potentially significant shortcomings in current estimates of the hemispheric impact of North American emissions on tropospheric ozone and should be evaluated in future studies.

Transport of biomass burning emissions from southern Africa

The transport of biomass burning emissions from southern Africa to the neighboring Atlantic and Indian Oceans during the dry season (May–October) of 2000 is characterized using ground, ozonesonde, and aircraft measurements of carbon monoxide (CO) and ozone (O3) in and around southern Africa, together with the GEOS‐CHEM global model of tropospheric chemistry. The model shows a positive bias of ∼20% for CO and a negative bias of ∼10–25% for O3 at oceanic sites downwind of fire emissions. Near areas of active fire emissions the model shows a negative bias of ∼60% and ∼30% for CO and O3, respectively, likely due to the coarse spatial (2° × 2.5°) and temporal (monthly) resolution of the model compared to that of active fires. On average, from 1994 to 2000, ∼60 Tg of carbon monoxide (CO) from biomass burning in southern Africa was transported eastward to the Indian Ocean across the latitude band 0°–60°S during the 6 months of the dry season. Over the same time period, ∼40 Tg of CO from southern African biomass burning was transported westward to the Atlantic Ocean over the latitudes 0°–20°S during the 6‐month dry season, but most of that amount was transported back eastward over higher latitudes to the south (21°–60°S). Eastward transport of biomass burning emissions from southern Africa enhances CO concentrations by ∼4–13 ppbv per month over the southern subtropical Indian Ocean during the dry season, with peak enhancements in September. Carbon monoxide from southern African and South American biomass burning is seen in the model simulations as far away as Australia, contributing ∼8 ppbv and ∼12–15 ppbv CO, respectively, and thus explaining the ∼20–25 ppbv observed enhancement of CO over Melbourne in mid‐September 2000.

Exploring the potential of combining column‐integrated atmospheric polarization with airborne in situ size distribution measurements for the retrieval of an aerosol model: A case study of a biomass burning plume during SAFARI 2000

Ground‐based columnar and airborne in situ measurements of aerosol optical properties acquired during the Southern African Regional Science Initiative (SAFARI 2000) in August–September 2000 are analyzed to retrieve the aerosol model of a haze layer affected by long‐range transport of biomass burning emissions. One case study is considered. A columnar value of the aerosol polarized phase function Qmeasp(Θ) and of the aerosol single scattering albedo ω0, both at 870 nm, are retrieved from measurements acquired by a ground‐based Sun/sky photometer, assuming that the surface albedo is 0.3. The maximum value of the polarized phase function is 0.37 ± 0.02 at a scattering angle of 70°, ω0 is 0.80 ± 0.05. The in situ particle size distribution is measured in a vertical profile over the ground‐based site by an airborne optical particle counter. Because the size distribution integrated over the column is inconsistent with the polarized phase function, aerosol concentration of the 0.25 μm mode is reduced by a factor of 7.5. Taking into account that the estimation of particle size depends on particle refractive index, it is found that the radius of absorbing particles cannot be larger than 0.15 μm for reproducing Qmeasp(Θ), suggesting external mixture of absorbing particles smaller than 0.15 μm with nonabsorbing particles larger than 0.15 μm. The imaginary part of the effective refractive index is estimated to be (0.09 ± 0.03)i. Comparing Ångström exponent obtained from Sun/sky photometer extinction measurements and the Ångström exponent calculated for the in situ measured aerosol size distribution acquired in eleven vertical profiles allows us to conclude that in most considered cases, the mixture of absorbing with nonabsorbing particles is external with a radius limit at around 0.15 μm.

Development of Global scale Chemical Transport Model (GCTM) and Its Application to the Transport of Biomass Burning Emissions

Global chemical transport model (GCTM) has been developed and applied to see effects of biomass burning sources on atmospheric chemical environment in southern hemisphere. The model includes processes of advection, diffusion, chemistry, sub-grid scale cumulus convection, and wet- and dry-depositions. The model's chemistry part includes 40 species and 97 chemical reactions. Simulations were performed for about one month in September and October, 1994, when strong biomass burning occurred under the climatic condition of ENSO. We focused especially on ozone formation over Equatorial Asia, and evaluated relative importance of its local production from the sources of anthropogenic and biomass burning, and soil NOx emissions, and also long range transport from mid-latitudinal southern hemisphere. The results could successfully explain the reason of the formation of complex ozone vertical structure observed over Java Island around 7.5S and 112.6E.

Convective transport of biomass burning emissions over Brazil during TRACE A

A series of large mesoscale convective systems that occurred during the Brazilian phase of GTE/TRACE A (Transport and Atmospheric Chemistry near the Equator‐Atlantic) provided an opportunity to observe deep convective transport of trace gases from biomass burning. This paper reports a detailed analysis of flight 6, on September 27, 1992, which sampled cloud‐ and biomass‐burning‐perturbed regions north of Brasilia. High‐frequency sampling of cloud outflow at 9–12 km from the NASA DC‐8 showed enhancement of CO mixing ratios typically a factor of 3 above background (200–300 parts per billion by volume (ppbv) versus 90 ppbv) and significant increases in NOx and hydrocarbons. Clear signals of lightning‐generated NO were detected; we estimate that at least 40% of NOx at the 9.5‐km level and 32% at 11.3 km originated from lightning. Four types of model studies have been performed to analyze the dynamical and photochemical characteristics of the series of convective events. (1) Regional simulations for the period have been performed with the NCAR/Penn State mesoscale model (MM5), including tracer transport of carbon monoxide, initialized with observations. Middle‐upper tropospheric enhancements of a factor of 3 above background are reproduced. (2) A cloud‐resolving model (the Goddard cumulus ensemble (GCE) model) has been run for one representative convective cell during the September 26–27 episode. (3) Photochemical calculations (the Goddard tropospheric chemical model), initialized with trace gas observations (e.g., CO, NOx, hydrocarbons, O3) observed in cloud outflow, show appreciable O3 formation postconvection, initially up to 7–8 ppbv O3/d. (4) Forward trajectories from cloud outflow levels (postconvective conditions) put the ozone‐producing air masses in eastern Brazil and the tropical Atlantic within 2–4 days and over the Atlantic, Africa, and the Indian Ocean in 6–8 days. Indeed, 3–4 days after the convective episode (September 30, 1992), upper tropospheric levels in the Natal ozone sounding show an average increase of ∼30 ppbv (3 Dobson units (DU) integrated) compared to the September 28 sounding. Our simulated net O3 production rates in cloud outflow are a factor of 3 or more greater than those in air undisturbed by the storms. Integrated over the 8‐ to 16‐km cloud outflow layer, the postconvection net O3 production (∼5–6 DU over 8 days) accounts for ∼25% of the excess O3 (15–25 DU) over the South Atlantic. Comparison of TRACE A Brazilian ozonesondes and the frequency of deep convection with climatology [Kirchhoff et al., this issue] suggests that the late September 1992 conditions represented an unusually active period for both convection and upper tropospheric ozone formation.