Biomass burning (BB) is a large source of primary and secondary organic aerosols (POA and SOA). This study addresses the physical and chemical evolution of BB organic aerosols. Firstly, the evolution and lifetime of BB POA and SOA signatures observed with the Aerodyne Aerosol Mass Spectrometer are investigated, focusing on measurements at high-latitudes acquired during the 2008 NASA ARCTAS mission, in comparison to data from other field studies and from laboratory aging experiments. The parameter <i>f</i>₆₀, the ratio of the integrated signal at <i>m/z</i> 60 to the total signal in the organic component mass spectrum, is used as a marker to study the rate of oxidation and fate of the BB POA. A background level of <i>f</i>₆₀~0.3% ± 0.06% for SOA-dominated ambient OA is shown to be an appropriate background level for this tracer. Using also <i>f</i>₄₄ as a tracer for SOA and aged POA and a surrogate of organic O:C, a novel graphical method is presented to characterise the aging of BB plumes. Similar trends of decreasing <i>f</i>₆₀ and increasing <i>f</i>₄₄ with aging are observed in most field and lab studies. At least some very aged BB plumes retain a clear <i>f</i>₆₀ signature. A statistically significant difference in <i>f</i>₆₀ between highly-oxygenated OA of BB and non-BB origin is observed using this tracer, consistent with a substantial contribution of BBOA to the springtime Arctic aerosol burden in 2008. Secondly, a summary is presented of results on the net enhancement of OA with aging of BB plumes, which shows large variability. The estimates of net OA gain range from ΔOA/ΔCO(mass) = −0.01 to ~0.05, with a mean &Delta;OA/POA ~19%. With these ratios and global inventories of BB CO and POA a global net OA source due to aging of BB plumes of ~8 ± 7 Tg OA yr⁻¹ is estimated, of the order of 5 % of recent total OA source estimates. Further field data following BB plume advection should be a focus of future research in order to better constrain this potentially important contribution to the OA burden

Emissions from gasoline and diesel vehicles are predominant anthropogenic sources of reactive gas-phase organic carbon and key precursors to secondary organic aerosol (SOA) in urban areas. Their relative importance for aerosol formation is a controversial issue with implications for air quality control policy and public health. We characterize the chemical composition, mass distribution, and organic aerosol formation potential of emissions from gasoline and diesel vehicles, and find diesel exhaust is seven times more efficient at forming aerosol than gasoline exhaust. However, both sources are important for air quality; depending on a region's fuel use, diesel is responsible for 65% to 90% of vehicular-derived SOA, with substantial contributions from aromatic and aliphatic hydrocarbons. Including these insights on source characterization and SOA formation will improve regional pollution control policies, fuel regulations, and methodologies for future measurement, laboratory, and modeling studies.motor vehicle emission factors | photochemical oxidation | urban air quality | volatile organic compound emissions | petroleum fuel composition O rganic aerosol (OA) in the atmosphere is detrimental to human health and represents a highly uncertain forcing of climate change (1). The use of petroleum-derived fuels is an important source of reactive gas-phase organic carbon that provides key precursors to the formation of secondary OA (SOA) and tropospheric ozone (1). Controlling these emissions from gasoline and diesel vehicles is central to air quality mitigation policies in urban areas (2). Previous work has concluded that further research is necessary to elucidate all organic sources of SOA precursors (3, 4). Significant controversy exists over the contributions of precursors from gasoline and diesel vehicles, and the relative importance of each for SOA formation remains in question, in part because of insufficient chemical characterization of fuels and emissions, and the difficulty of ambient measurements of gasphase compounds emitted from diesel sources (1, 4-8).In the United States, diesel fuel accounts for 21% of on-road fuel use (by volume), with off-road sources increasing total use to 28% diesel. In California, the diesel share of on-road use ranges from approximately 10% in coastal cities to more than 30% in agricultural regions (SI Appendix, Table S1) (2, 9, 10). Noncombusted hydrocarbons from the fuels are emitted in the exhaust of gasoline and diesel engines, and also via evaporation from gasoline vehicles and service stations. These compounds in unburned gasoline and diesel fuel dominate vehicular emissions of reactive gas-phase carbon that have the potential to form SOA (11,12). Previous work has shown nontailpipe emissions account for ∼30% of gasoline-related emissions in urban regions, but limited work exists constraining the emissions and SOA formation potential of gas-phase organic carbon from gasoline and diesel sources (13). By using extensive fuel analyses and field data from two sites that include ...

Speciated particle-phase organic nitrates (pONs) were quantified using online chemical ionization MS during June and July of 2013 in rural Alabama as part of the Southern Oxidant and Aerosol Study. A large fraction of pONs is highly functionalized, possessing between six and eight oxygen atoms within each carbon number group, and is not the common first generation alkyl nitrates previously reported. Using calibrations for isoprene hydroxynitrates and the measured molecular compositions, we estimate that pONs account for 3% and 8% of total submicrometer organic aerosol mass, on average, during the day and night, respectively. Each of the isoprene-and monoterpenes-derived groups exhibited a strong diel trend consistent with the emission patterns of likely biogenic hydrocarbon precursors. An observationally constrained diel box model can replicate the observed pON assuming that pONs (i) are produced in the gas phase and rapidly establish gasparticle equilibrium and (ii) have a short particle-phase lifetime (∼2-4 h). Such dynamic behavior has significant implications for the production and phase partitioning of pONs, organic aerosol mass, and reactive nitrogen speciation in a forested environment. O rganic nitrates (ONs; ON = RONO 2 + RO 2 NO 2 ) are an important reservoir, if not sink, of atmospheric nitrogen oxides (NO x = NO + NO 2 ). ONs formed from isoprene oxidation alone are responsible for the export of 8-30% of anthropogenic NO x out of the US continental boundary layer (1, 2). Regional NO x budgets and tropospheric ozone (O 3 ) production are, therefore, particularly sensitive to uncertainties in the yields and fates of ON (3-6). The yields implemented in modeling studies are determined from laboratory experiments, in which only a few of the first generation gaseous ONs or the total gas-phase ONs and particle-phase organic nitrates (pONs) have been quantified, whereas production of highly functionalized ONs capable of strongly partitioning to the particle phase have been inferred (7-11) or directly measured in the gas phase (12). Addition of a nitrate (-ONO 2 ) functional group to a hydrocarbon is estimated to lower the equilibrium saturation vapor pressure by 2.5-3 orders of magnitude (13). Thus, ON formation can enhance particle-phase partitioning of semivolatile species in regions with elevated levels of nitrogen oxides, contributing to secondary organic aerosol (SOA) growth (8). However, highly time-resolved measurements of speciated ON in the particle phase have been lacking.We use a recently developed high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS) using iodide-adduct ionization (14) with a filter inlet for gases and aerosols (FIGAERO) (15) that allows alternating in situ measurements of the molecular SignificanceWe present online field observations of the speciated molecular composition of organic nitrates in ambient atmospheric particles utilizing recently developed high-resolution MS-based instrumentation. We find that never-before-identified low-volatility organi...