Shiro Hatakeyama

Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically-influenced Northern Hemisphere midlatitudes

[1] 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.

Reactions of OH with α‐pinene and β‐pinene in air: Estimate of global CO production from the atmospheric oxidation of terpenes

Reactions of OH with α-pinene and β-pinene were studied for the purpose of obtaining the basic data to estimate the emission rate of CO from the photooxidation of terpenes in the atmosphere. In the presence of NO the main product was pinonaldehyde and 6,6-dimethyl-bicyclo[3.1.1]heptan-2-one from α- and β-pinene, respectively, and the yield was 56±4 and 79±8%, respectively. In the absence of NO the yield was remarkably lower, and the yield of organic aerosols was enhanced. For α-pinene 56±3% was obtained as a yield of aerosols on the carbon number basis. Gross annual emission of CO from the reactions of OH with terpenes was estimated to be 22 Tg C yr−1 (50 Tg CO yr−1) by regarding α-pinene as the representative of terpenes, on the basis of the annual emission rate of terpenes, estimated lifetime of pinenes in the atmosphere, the apparent rate constant for the intermediate to form CO, and the estimated yield of CO from the secondary oxidation of pinonaldehyde. The ultimate yield of CO from the tropospheric oxidation of terpenes (including both ozone and OH reactions) was estimated to be 20% on the carbon number basis, and the total annual emission of CO was evaluated to be 96 Tg C yr−1 (222 Tg CO yr−1).

OH radical‐ initiated photooxidation of isoprene: An estimate of global CO production

The OH radical- initiated photooxidation of isoprene has been investigated experimentally by a 6-m3 photochemical reaction chamber equipped with a long path length Fourier transform infrared spectrometer. In the presence of NOx, the major primary reaction products were methyl vinyl ketone, methacrolein, and formaldehyde. Their yields were in quantitative agreement with previous measurements. In the absence of NOx, the reaction mechanism was found to be quite different from that in the presence of NOx, and major reaction products observed in the infrared spectra were attributed to organic hydroperoxides. Based on the model experiments, the ultimate yield of CO was evaluated to be 60% on the carbon number basis in the presence of NOx and 23% in the absence of NOx. The CO yield in the real atmosphere was evaluated as 30% on the carbon number basis, and global annual CO production from isoprene was estimated to be 105 Tg C yr−1. Together with a previous estimate of the CO production from terpenes, global CO production from natural hydrocarbons was evaluated to be 200±60 Tg C yr−1.

Long‐range transport of ozone in the East Asian Pacific rim region

Measurements of surface ozone were conducted at three remote island sites in the East Asian Pacific rim region during the Pacific Exploratory Mission-West (A) campaign period in September–October, 1991. The ozone concentrations observed at the three measurement stations at Oki and Okinawa, Japan, and Kenting, Taiwan, had similar ranges varying between 6–63, 8–58, and 4–65 ppb, respectively, except for one event of short-range transport of polluted air at Kenting. Day-to-day variations have been analyzed by using backward air parcel trajectories on isentropic surfaces. The results showed that continental air masses which originated from northwestern Asia and passed through the high anthropogenic emission region of East Asia contained the highest concentration of ozone, 30–60 ppb with an average of 43–45 ppb at the three stations. In contrast, the lowest concentrations were observed for air parcels originating from the mid-Pacific and transported without mixing with the continental outflow. These parcels contained 5–20 ppb of ozone with the average of 11, 15, and 9 ppb at Oki, Okinawa, and Kenting, respectively. The air parcels from the South China Sea contained 22 and 18 ppb of ozone at Okinawa and Kenting, respectively, which were higher than those from mid-Pacific. Continental air mass from the north-northeast to Oki containing 35–40 ppb ozone with the average of 37 ppb was recognized as continental “background.” The high ozone concentrations in the northwesterly continental outflow exceeding the background was ascribed to photochemical buildup in the planetary boundary layer.

Yield of SO2 and formation of aerosol in the photo-oxidation of DMS under atmospheric conditions

Abstract Photo-oxidation of DMS under atmospheric conditions was studied both in dry ( [H 2 O] ppm ) and in humid air (relative humidity ~ 35%at 30°C). Yield of SO 2 was 21 ± 5% at the early stage of reaction and finally increased to 29 ± 7% . Formation of aerosols were also measured. In dry air number concentration of aerosols was low (max. ~ 3.0 × 10 -3 cm −3 ). but geometrical mean diameter was large (~ 0.4 μm). In humid air number density of aerosols was high (max. ~ 3 × 10 5 cm -3 ), but geometrical mean diameter was small (~ 0.2 μm). Dimensionless parameter ( A/(N 1 3 V 2 3 ) ) was calculated to be 4.35 for the humid air system. Both methanesulfonic acid (CH 3 SO 3 H, MSA) and sulfuric acid were detected in sampled aerosols.

Measurements of NO, NO y , CO and O3 and estimation of the ozone production rate at Oki Island, Japan, during PEM‐West

Measurements of NO, NOy, CO, and O3 were conducted at Oki Island, 65 km west of the Japanese mainland during September–October 1991. The results show that the Oki Island site is relatively clean with mean (and median) CO and NOy concentrations of 137 (130) ppbv and 713 (505) pptv, respectively. These relatively low concentrations reflect the frequent occurrence of windsfrom the less populated regions to the north during this campaign. During several periods, elevated CO, NOy, and O3 concentrations were associated with transport of pollutants from Japan and Korea. CO and NOy are significantly correlated in the entire data set, reflecting the overall influence of anthropogenic emissions. Mean CO and NOy concentrations show small diurnal cycles with a maximum in the morning and early evening hours. Hourly mean O3 concentrations exhibit a diurnal cycle of amplitude 3.5 parts per billion by volume, with a maximum in the early afternoon attributed to photochemical O3 production. The source of this afternoon O3 enhancement is analyzed using regression analysis of O3 and NOy and of O3 and CO. Both NOy and CO are significantly correlated with O3 during the daytime but are poorly or insignificantly correlated with O3 at night, indicating that upwind photochemistry operating within the previous ∼1 day was responsible for the observed afternoon O3 enhancement. The NOy-O3 regression analysis indicates formation of ∼9 O3 molecules per NOy molecule reaching Oki Island. The mean and median midday NO concentrations of 55 and 23 parts per trillion by volume, respectively, were sufficient to support net production of O3. Using the results of these measurements and prior modeling studies (Lin et al., 1988), we estimate a “lifetime-averaged” O3 production efficiency of 10 molecules O3 per NOx molecule. Combined with estimated East Asian NOx emissions for 1987, this indicates an annual O3 production of 1.0 × 1014 g O from photochemistry which is approximately 2 times the annual stratospheric flux in this region. This value must be considered as a rough estimate but is probably accurate to within a factor of 2.

Reaction of ketenes with atomic oxygen

Rate constants for the reaction of atomic oxygen with ketene, and methyl, ethyl, and dimethyl ketene were measured over a temperature range of 230–449 K using the pulse radiolysis resonance absorption system. Over the temperature range of the experiments, the rate data could be fitted by Arrhenius expressions: O+CH2CO, (2.92±0.78)×10−12exp[(−1349±154 cal mol−1)/RT]; O+(CH3)CHCO, (4.79±1.31)×10−12exp[(494.9±163.2 cal mol−1)/RT]; O+(C2H5)CHCO, (5.36±0.83)×10−12exp[(444.6±94.0 cal mol−1)/RT]; O+(CH3)2CCO, (5.92±0.94)×10−12exp[(1131±85 cal mol−1)/RT]; in units of cm3 molecule−1 s−1. The rate constants at room temperature were also determined using a discharge‐flow system coupled to a photoionization mass spectrometer. Rate constants obtained are 0.043±0.04, 1.16±0.13, 1.36±0.11, and 6.04±0.64×10−11 cm−3 molecule−1 s−1 for CH2CO, (CH3)CHCO, (C2H5)CHCO, and (CH3)2CCO, respectively. Several reaction products were analyzed by the photoionization mass spectrometer.

Characterization of atmospheric air pollutants at two sites in northern Kyushu, Japan - Chemical form, and chemical reaction

Airborne gaseous and particulate matter in winter was measured over for 37 days in January and December 1997 at 2 sampling sites in northern Kyushu, Japan. One sampling site, Goto Island (an isolated island in the East China Sea), was about 200 km southwest of the other sampling site, Dazaifu city. In winter, acidic sulfates generated over the East Asian continent were transported to northwest Kyushu, to places such as Goto Island and the inland Kyushu area, and high sulfate concentrations were observed at the 2 sampling sites when strong NW winds blew. Acidity around Goto was mainly influenced by particulate NH4HSO4. The concentrations of NH3 at Goto Island were lower than at Dazaifu city. The difference in NH3 levels at the 2 sampling sites plays an important role in the chemical forms and sizes of the particulate matter. Nitrates at Goto Island were mostly present as NaNO3 and Ca(NO3)2 in coarse-size particles. During the process of long-range transport of air pollutants from the Asian continent to Goto, gaseous HNO3 was produced by a photochemical reactions of nitrogen oxides in the atmosphere, and particulate NaNO3 and gaseous HCl were formed by a chlorine-loss reaction between NaCl and gaseous HNO3. When strong NW winds blew, acidic sulfates together with some of the NaNO3 and/or Ca(NO3)2 and some of gaseous HCl and HNO3, which exist in the sea to the west of Kyushu and Goto Island, were transported to inland Kyushu such as Dazaifu city. During the process of transport, most of the acidic sulfates and acidic gases were mixed with regional air pollutants such as chlorides and nitrates existing around Dazaifu city, and neutralized forming (NH4)2SO4, NH4Cl and NH4NO3 in an environment of excess NH3. Therefore, the main chemical forms of NO3− at Dazaifu city varied day-by-day from fine-sized NH4NO3 to coarse-sized NaNO3 and/or Ca(NO3)2. The appearance of NO3− in coarse-size particles at Dazaifu city was due to the transport of NO3− from around the sea to the west of Kyushu.

Transport of Atmospheric Pollutants from East Asia

Air-borne measurements of air pollutants transported from northeast Asia to Japan and the Pacific Ocean were carried out three times from 1996 to 1999 over the seas between Japan and Asian Continent. Those campaigns were named PEACAMPOT II under auspices of the IGAC/APARE program. A transport pattern of a highly polluted air mass from central China was found. Such air mass was driven by the quick movement of low pressure traveling from Taiwan area to the northeast of Japan. This finding supported well the results of modeling studies for long-range transport of atmospheric pollutants from East Asia.

The 1991 PEACAMPOT aircraft observation of ozone, NO x , and SO2 over the East China Sea, the Yellow Sea, and the Sea of Japan

Atmospheric pollutants over northwest Pacific Rim region (the East China Sea, the Yellow Sea, and the Sea of Japan) were observed from an airplane from October 5 to October 11, 1991, as one of the first intensive field studies of the International Global Atmospheric Chemistry/East Asian North Pacific Regional Experiment (IGAC/APARE). Ozone, NOx, Aerosols, SO2, hydrocarbons, CO, and aldehydes were measured. In this paper, the results of this experiment for ozone, NOx and SO2 measurements are described. Ozone and NOx were negatively correlated, which is contrary to the normal correlation observed in background areas. We believe that this is due to the large contribution of the upper atmosphere in most cases. The vertical distribution of SO2 concentrations indicates the impact of the Asian continental air mass.