Biomass burning (BB) is the second largest source of trace gases and the largest source of primary fine carbonaceous particles in the global troposphere. Many recent BB studies have provided new emission factor (EF) measurements. This is especially true for non-methane organic compounds (NMOC), which influence secondary organic aerosol (SOA) and ozone formation. New EF should improve regional to global BB emissions estimates and therefore, the input for atmospheric models. In this work we present an up-to-date, comprehensive tabulation of EF for known pyrogenic species based on measurements made in smoke that has cooled to ambient temperature, but not yet undergone significant photochemical processing. All EFs are converted to one standard form (g compound emitted per kg dry biomass burned) using the carbon mass balance method and they are categorized into 14 fuel or vegetation types. Biomass burning terminology is defined to promote consistency. We compile a large number of measurements of biomass consumption per unit area for important fire types and summarize several recent estimates of global biomass consumption by the major types of biomass burning. Post emission processes are discussed to provide a context for the emission factor concept within overall atmospheric chemistry and also highlight the potential for rapid changes relative to the scale of some models or remote sensing products. Recent work shows that individual biomass fires emit significantly more gas-phase NMOC than previously thought and that including additional NMOC can improve photochemical model performance. A detailed global estimate suggests that BB emits at least 400 Tg yr⁻¹ of gas-phase NMOC, which is almost 3 times larger than most previous estimates. Selected recent results (e.g. measurements of HONO and the BB tracers HCN and CH₃CN) are highlighted and key areas requiring future research are briefly discussed

Isoprene is a significant source of atmospheric organic aerosol; however, the oxidation pathways that lead to secondary organic aerosol (SOA) have remained elusive. Here, we identify the role of two key reactive intermediates, epoxydiols of isoprene (IEPOX ¼ β-IEPOX þ δ-IEPOX) and methacryloylperoxynitrate (MPAN), which are formed during isoprene oxidation under low-and high-NO x conditions, respectively. Isoprene low-NO x SOA is enhanced in the presence of acidified sulfate seed aerosol (mass yield 28.6%) over that in the presence of neutral aerosol (mass yield 1.3%). Increased uptake of IEPOX by acid-catalyzed particle-phase reactions is shown to explain this enhancement. Under high-NO x conditions, isoprene SOA formation occurs through oxidation of its secondgeneration product, MPAN. The similarity of the composition of SOA formed from the photooxidation of MPAN to that formed from isoprene and methacrolein demonstrates the role of MPAN in the formation of isoprene high-NO x SOA. Reactions of IEPOX and MPAN in the presence of anthropogenic pollutants (i.e., acidic aerosol produced from the oxidation of SO 2 and NO 2 , respectively) could be a substantial source of "missing urban SOA" not included in current atmospheric models.acid-catalyzed particle-phase reactions | epoxides | methacryloylperoxynitrate | organosulfates I soprene (2-methyl-1,3-butadiene, C 5 H 8 ) is the most abundant nonmethane hydrocarbon emitted into the Earth's atmosphere, with emissions estimated to be 440-660 TgC yr −1 (1). The atmospheric hydroxyl (OH) radical-initiated oxidation of isoprene, so-called photooxidation, plays a key role in establishing the balance of hydrogen oxide (HO x ¼ OH þ HO 2 ) radicals in vegetated areas (2, 3) and influences urban ozone formation in populated areas blanketed with biogenic emissions (4). Formation of low-volatility compounds during isoprene oxidation has been estimated to be the single largest source of atmospheric organic aerosol [i.e., secondary organic aerosol (SOA)] (5-8).The photooxidation of unsaturated volatile organic compounds (VOCs) proceeds through formation of a hydroxy peroxy (RO 2 ) radical, the fate of which depends on the concentration of nitrogen oxides (NO x ¼ NO þ NO 2 ). Higher SOA yields from isoprene are observed under low-NO x (or NO x -free) conditions; in this regime, RO 2 radicals react primarily with HO 2 , a pathway that tends to produce lower-volatility oxidation products than that involving the reaction of RO 2 with NO (9-11). Under high-NO x conditions, RO 2 radicals react with NO to produce alkoxy (RO) radicals, or as a minor pathway, organic nitrates (RONO 2 ). For small VOCs (≤C 10 ), like isoprene, these RO radicals generally fragment into smaller more volatile products, resulting in small amounts of SOA (9-11). Despite the fact that SOA from isoprene has been extensively studied (8), the chemical pathways to its formation under both low-and high-NO x conditions have remained unclear. In this study we examine the mechanism of isoprene SOA formation in these two ...

No NO Isoprene, a five-carbon diene produced by plants, is the most abundant nonmethane hydrocarbon released into the atmosphere and plays an important role in tropospheric chemistry. Isoprene is also thought to affect climate by acting as a source of atmospheric aerosols. Paulot et al. (p. 730 ; see the Perspective by Kleindienst ) now describe how isoprene may lead to the formation of secondary organic aerosols. In laboratory experiments, the photooxidation of isoprene in low-NO conditions, such as those which occur in vegetated regions far from anthropogenic influence, produced high yields of dihydroxy epoxides, a suspected precursor of the aerosols. This discovery could help to explain some of the more puzzling aspects of isoprene chemistry in remote regions.

A global network of ground-based Fourier transform spectrometers has been founded to remotely measure column abundances of CO 2 , CO, CH 4 , N 2 O and other molecules that absorb in the near-infrared. These measurements are directly comparable with the near-infrared total column measurements from space-based instruments. With stringent requirements on the instrumentation, acquisition procedures, data processing and calibration, the Total Carbon Column Observing Network (TCCON) achieves an accuracy and precision in total column measurements that is unprecedented for remotesensing observations (better than 0.25% for CO 2 ). This has enabled carbon-cycle science investigations using the TCCON dataset, and allows the TCCON to provide a link between satellite measurements and the extensive ground-based in situ network.

We present an estimate of net CO2 exchange between the terrestrial biosphere and the atmosphere across North America for every week in the period 2000 through 2005. This estimate is derived from a set of 28,000 CO2 mole fraction observations in the global atmosphere that are fed into a state-of-the-art data assimilation system for CO2 called CarbonTracker. By design, the surface fluxes produced in CarbonTracker are consistent with the recent history of CO2 in the atmosphere and provide constraints on the net carbon flux independent from national inventories derived from accounting efforts. We find the North American terrestrial biosphere to have absorbed ؊0. carbon cycle ͉ greenhouse gases ͉ data assimilation ͉ biogeochemistry ͉ atmospheric composition