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.

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The dark reaction of NO, and HzO vapor in 1 atm of air was studied for the purpose of elucidating the recently discussed unknown radical source in smog chambers. Nitrous acid and nitric oxide were found to be formed by the reaction of NO2 and H2O in an evacuable and bakable smog chamber. No nitric acid was observed in the gas phase. The reaction is not stoichiometric and is thought to be a heterogeneous wall reaction. The reaction rate is first order with respect to NO2 and HzO, and the concentrations of HONO and NO initially increase linearly with time. The same reaction proceeds with a different rate constant in a quartz cell, and the reaction of NO2 and H2180 gave H180N0 exclusively. Taking into consideration the heterogeneous reaction of NO2 and HzO, the upper limit of the rate constant of the third-order reaction NO + NO2 + HzO -2HONO was deduced to be (3.0 f 1.4) X ppm-2.min-1, which is one order of magnitude smaller than the previously reported value.Nitrous acid formed by the heterogeneous dark reaction of NO2 and H20 should contribute significantly to both an initially present HONO and a continuous supply of OH radicals by photolysis in smog chamber experiments.

Reactions of OH with a-pinene and (260 Tg C yr -•, ~25%) and larger than that from •-pinene were studied for the purpose of fossil fuel combustion (190 Tg C yr -1 ~18%) obtaining the basic data to estimate the emission [World Meteorological Organization (•40), •986]. rate of CO from the photooxidation of terpenes in The measurement of the concentration of tropothe atmosphere. In the presence of NO the main spheric CO from a space shuttle [Reichle et al., product was pinonaldehyde and 6,6-dimethyl-1986] revealed that the highest concentration of bicyclo[3.1.1]heptan-2-one from •-and •-pi-CO was recorded above South AmeriCa and central nene, respectively, and the yield was 56 ñ 4 and Africa. It indicates the importance of the 79 ñ 8%, respectively. In the absence of NO the photooxidation of natural hydrocarbons emitted yield was remarkably lower, and the yield of from tropical rain forests as well as the direct organic aerosols was enhanced. For •-pinene 56 emission of CO from biomass burning. ñ 3 % was obtained as a yield of aerosols on the Monoterpenes are among the most important carbon number basis. Gross annual emission of CO natural hydrocarbons, and their atmospheric from the reactions of OH with terpenes was esti-reactions play an essential part in the global mated to be 22 Tg C yr-1 (50 Tg CO yr-•) by carbon cycle. The global emission rates of regarding • -pinerie as the representative of terpenes were estimated to be 175-830 Tg yr-1 terpenes, on the basis of the annual emission [Went, 1960; Robinson and Robbins, 1968; rate of terpenes, estimated lifetime of pinches Rasmussen, 1972; Zimmerman et al., 1978], which in the atmosphere, the apparent rate constant for exceed the emission rates of anthropogenic hydrothe intermediate to form CO, and the estimated carbons' 65-75 Tg yr-• [Duce, 1978; Robinson, yield Of CO from the secondary oxidation of 1978]. However, only very limited information is pinonaldehyde. The ultimate yield of CO from the available so far on the formation of CO from the tropospheric oxidation of terpenes (including photooxidation of terpenes. Hanst et al. [1980] both ozone and OH reactions) was estimated to be estimated the yield of CO from the oxidation of 20% on the carbon number basis, and the total terpenes by use of C1 atoms in place of OH radiannual emission of CO was evaluated to be 96 Tg C cals. Recently, we reported [Hatakeyama et al., yr-1 (222 Tg CO yr-1). 1989] the estimate of the ultimate yield of CO from the oxidation of terpenes initiated by Introduction ozone, and the gross annual emission of CO with respect to the ozone-terpene reactions was esti-Carbon monoxide (CO) plays a major role in mated to be 74 Tg C yr-• In order to obtain a controlling the concentration of OH radicals in more complete estimate o• CO emission the yield the atmosphere. OH radicals are known to be the of CO from the oxidation of terpenes initiated by most important atmospheric trace species which OH radicals is needed, since terpenes are condetermine the lifetime of most of the other sumed by both ...