Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.

Organic aerosol (OA) data acquired by the Aerosol Mass Spectrometer (AMS) in 37 field campaigns were deconvolved into hydrocarbon‐like OA (HOA) and several types of oxygenated OA (OOA) components. HOA has been linked to primary combustion emissions (mainly from fossil fuel) and other primary sources such as meat cooking. OOA is ubiquitous in various atmospheric environments, on average accounting for 64%, 83% and 95% of the total OA in urban, urban downwind, and rural/remote sites, respectively. A case study analysis of a rural site shows that the OOA concentration is much greater than the advected HOA, indicating that HOA oxidation is not an important source of OOA, and that OOA increases are mainly due to SOA. Most global models lack an explicit representation of SOA which may lead to significant biases in the magnitude, spatial and temporal distributions of OA, and in aerosol hygroscopic properties.

[1] Aerosol chemical composition and gaseous species were measured at Cape Hedo, Okinawa, Japan (CHO), during the ABC/EAREX project period in March 2005, using high-time-resolution instruments including an Aerodyne quadrupole aerosol mass spectrometer (Q-AMS), a tapered element oscillating microbalance (TEOM), and gas monitors in order to investigate the transport and subsequent chemical transformation of aerosol in the east Asian region. Sulfate was the dominant species in fine aerosol mode and the average concentration of ammonium, sulfate and organics was 1.25, 6.37 and 2.16 mg m À3 , respectively. The sulfate concentration observed at CHO in 2005 was about 1.5-2 times higher than that in 1994. For the majority of high-sulfate observations, the air mass was transported from the central east Chinese region (between Shanghai and the Shandong Peninsula). Sulfate transport was intermittent and strongly correlated with the passage of synoptic-scale high-/low-pressure systems. Chemical components and their concentration showed significant change on 17-18 March, which is accounted for by the change in air mass origin and the synoptic-scale weather system. In addition, it is suggested that the difference of air quality at the air mass origin reflects the chemical composition at CHO. The high sulfate concentration required heterogeneous conversion of SO 2 to sulfate at a rate of 2.0% h À1 . A pronounced signal at m/z = 44 confirmed that organic compounds were oxidized.

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Aerosol chemical species were measured using an Aerodyne quadrupole aerosol mass spectrometer (Q-AMS) in spring 2010, in Fukuoka. The main species were sulfate and organics. Organic data were analyzed using the Positive Matrix Factorization (PMF) method. Two distinct periods (Period 1 and 2) were selected. Period 1 (from March 19 at 19:50 to March 20 at 10:00) was influenced by trans-boundary air pollution. Low-volatile, oxygenated organic aerosols (LV-OOA) were dominant and the hydrocarbon-like organic aerosols (HOA) fraction was as low as 15%. About one-fourth (26%) of the observation period in Fukuoka was influenced by trans-boundary air pollution. In Period 2 (from March 22 at 00:00 to March 22 at 23:50), both local emissions and trans-boundary air pollutants influenced Fukuoka air quality. The HOA fraction was relatively high, although the LV-OOA fraction was about one-third of OA. The trans-boundary air pollution was analyzed using the oxidation state of organic aerosols (OA), obtained by the PMF method.