Yugo Kanaya - Academia.edu (original) (raw)
Papers by Yugo Kanaya
Atmospheric Chemistry and Physics, 2009
An observation-based box model approach was undertaken to estimate concentrations of OH, HO 2 , a... more An observation-based box model approach was undertaken to estimate concentrations of OH, HO 2 , and RO 2 radicals and the net photochemical production rate of ozone at the top of Mount Tai, located in the middle of Central East China, in June 2006. The model calculation was constrained by the measurements of O 3 , H 2 O, CO, NO, NO 2 , hydrocarbon, HCHO, and CH 3 CHO concentrations, and temperature and J values. The net production rate of ozone was estimated to be 6.4 ppb h −1 as a 6-h average (09:00-15:00 CST), suggesting 58±37 ppb of ozone is produced in one day. Thus the daytime buildup of ozone recorded at the mountain top as ∼23 ppb on average is likely affected by in situ photochemistry as well as by the upward transport of polluted air mass in the daytime. On days with high ozone concentrations (hourly values exceeding 100 ppb at least once), in situ photochemistry was more active than it was on low ozone days, suggesting that in situ photochemistry is an important factor controlling ozone concentrations. Sensitivity model runs for which different NO x and hydrocarbon concentrations were assumed suggested that the ozone production occurred normally under NO x-limited conditions, with some exceptional periods (under volatile-organic-compound-limited conditions) in which there was fresh pollution. We also examined the possible influence of the heterogeneous loss of gaseous HO 2 radicals in contact with aerosol particle surfaces on the rate and regimes of ozone production.
Atmospheric Chemistry and Physics Discussions, 2013
Aerosol samples (TSP, n = 58) were collected on day-and night-time basis at Mangshan in the north... more Aerosol samples (TSP, n = 58) were collected on day-and night-time basis at Mangshan in the north of Beijing, China in autumn 2007 to better understand the status of air quality and the influence of urban pollutants in the northern vicinity of Beijing. The samples were analyzed for aerosol mass, total carbon (TC), low molecular weight α, ω-dicarboxylic acids (C 2-C 12), ketoacids (ωC 2-ωC 9 , pyruvic acid), αdicarbonyls (glyoxal and methylglyoxal), as well as aromatic (phthalic, iso-and terephthalic) diacids. Aerosol mass and TC concentrations are higher in daytime than in nighttime. TC/aerosol mass ratios in this study are lower than those reported in megacities in East Asia, but higher than those reported in marine aerosols. Molecular distributions of diacids demonstrated that oxalic (C 2) acid was the most abundant species, comprising 38-77 % of total diacids, followed by succinic (C 4) and malonic (C 3) acids. For most compounds, the concentrations were higher in daytime than nighttime, indicating that diacids are produced in daytime by photochemical oxidation of organic precursors emitted from anthropogenic sources in Beijing during the transport to Mangshan area by the northward wind. However, we found that C 2 concentrations are higher in nighttime than in daytime. A positive correlation of C 2 to glyoxylic acid (ωC 2) was obtained at night when relative humidity increased up to 100 %, suggesting that aqueous phase production of C 2 occurs in nighttime via the oxidation of ωC 2. Depletion of C 2 by photolysis of Fe-oxalato complexes might be another reason for the lower concentrations of C 2 in daytime samples. High phthalic acid/C 4 ratios in the aerosol samples suggest that automobile combustion and coal burning products are important sources, which are subjected to photochemical oxidation during the atmospheric transport of urban aerosols from Beijing. In contrast, higher concentrations of methylglyoxal in nighttime than daytime may suggest that isoprene emitted from the northern forest area is oxidized in daytime and then transported to the sampling area at night by northerly winds. This study demonstrates that secondary organic aerosols are significantly produced and aged in the vicinity of Beijing during atmospheric transport.
Journal of Geophysical Research: Atmospheres, 2015
The emission factors (EFs) of non-methane volatile organic compounds (NMVOCs) emitted during the ... more The emission factors (EFs) of non-methane volatile organic compounds (NMVOCs) emitted during the burning of Chinese crop residue were investigated as a function of modified combustion efficiency (MCE) in laboratory experiments. NMVOCs, including acetonitrile, aldehydes/ketones, furan, and aromatic hydrocarbons, were monitored by proton-transfer-reaction mass spectrometry (PTR-MS). Rape plant was burned in dry conditions and wheat straw was burned in both wet and dry conditions to simulate the possible burning of damp crop residue in regions of high temperature and humidity. We compared the present data to field data reported by Kudo et al [2014] Good agreement between field and laboratory data was obtained for aromatics under
Diurnal variations of carbonaceous components, major ions, and stable carbon and nitrogen isotope ratios in suburban aerosols from northern vicinity of Beijing
Atmospheric Environment, 2015
Abstract We report diurnal variations of organic carbon (OC), elemental carbon (EC), water-solubl... more Abstract We report diurnal variations of organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and major ions as well as stable carbon and nitrogen isotope ratios (δ 13 C and δ 15 N) in ambient aerosols at a suburban site (Mangshan), 40 km north of Beijing, China. We found that aerosol chemical compositions were largely controlled by the air mass transport from Beijing in daytime with southerly winds and by relatively fresh air mass in nighttime from the northern forest areas with northerly winds. Higher concentrations of aerosol mass and total carbon were obtained in daytime. Further, higher OC/EC ratios were recorded in daytime (4.0 ± 1.7) than nighttime (3.2 ± 0.7), suggesting that OC is formed by photochemical oxidation of gaseous precursors in daytime. Contributions of WSOC to OC were slightly higher in daytime (38%) than nighttime (34%), possibly due to secondary formation of WSOC in daytime. We also found higher concentrations of Ca 2+ in daytime, which was originated from the construction dust in Beijing area and transported to the sampling site. δ 13 C ranged from −25.3 to −21.2‰ (ave. −23.5 ± 0.9‰) in daytime and −29.0 to −21.4‰ (−24.0 ± 1.5‰) in nighttime, suggesting that Mangshan aerosols were more influenced by fossil fuel combustion products in daytime and by terrestrial C 3 plants in nighttime. This study suggests that daytime air mass delivery from megacity Beijing largely influence the air quality at the receptor site in the north together with photochemical processing of organic aerosols during the atmospheric transport, whereas the Mangshan site is covered with relatively clean air masses at night.
Journal of Geophysical Research: Atmospheres, 2014
Open crop residue burning is one of the major sources of air pollutants including the precursors ... more Open crop residue burning is one of the major sources of air pollutants including the precursors of photooxidants like ozone and secondary organic aerosol. We made measurements of trace gases including nonmethane volatile organic compounds (NMVOCs) in a rural area in central East China in June 2010. During the campaign, we identified six biomass burning events in total through the simultaneous enhancement of carbon monoxide and acetonitrile. Four cases represented fresh plumes (<2 h after emission), and two cases represented aged plumes (>3 h after emission), as determined by photochemical age. While we were not able to quantify formic acid, we identified an enhancement of major oxygenated volatile organic compounds (OVOCs) as well as low molecular alkanes and alkenes, and aromatic hydrocarbons in these plumes. The observed normalized excess mixing ratios (NEMRs) of OVOCs and alkenes showed dependence on air mass age, even in fresh smoke plumes, supporting the view that these species are rapidly produced and destructed, respectively, during plume evolution. Based on the NEMR data in the fresh plumes, we calculated the emission factors (EFs) of individual NMVOC. The comparison to previous reports suggests that the EFs of formaldehyde and acetic acid have been overestimated, while those of alkenes have been underestimated. Finally, we suggest that open burning of wheat residue in China releases about 0.34 Tg NMVOCs annually. If we applied the same EFs to all crops, the annual NMVOC emissions would be 2.33 Tg. The EFs of speciated NMVOCs can be used to improve the existing inventories.
GEOCHEMICAL JOURNAL, 2015
by chemical reactions involving precursor gases such as SO 2 , NO X , and volatile organic compou... more by chemical reactions involving precursor gases such as SO 2 , NO X , and volatile organic compounds in the atmosphere. PM 2.5 is derived from anthropogenic or natural sources including fuel combustion in power plants and transport, biomass burning, vegetation, volcanoes, and dust. In Japan, an environmental standard for PM 2.5 was newly established in September 2009, with an annual mean value of 15 mg m-3 and a daily mean value of 35 mg m-3. Since then, the number of monitoring sites for PM 2.5 has been increased by the Japanese Ministry of the Environment (MOE) to understand the status of PM 2.5 pollution over Japan. Observations made by the MOE have indicated that an achievement ratio of the environmental standard determined at the ambient monitoring stations is about 30% for the fiscal years 2010 and 2011 (http:// www.env.go.jp/air/osen/jokyo_h23/index.html). The monitoring stations at which PM 2.5 mass concentrations exceed the environmental standard are concentrated in the western part of Japan. In addition, Kanaya et al. (2010) reported that the PM 2.5 concentration at Fukue Island,
Direct measurements of HOx radicals in the marine boundary layer: testing the current tropospheric chemistry mechanism
Chemical record (New York, N.Y.), 2002
OH and HO(2) radicals, atmospheric detergents, and the reservoir thereof, play central roles in t... more OH and HO(2) radicals, atmospheric detergents, and the reservoir thereof, play central roles in tropospheric chemistry. In spite of their importance, we had no choice but to trust their concentrations predicted by modeling studies based on known chemical processes. However, recent direct measurements of these radicals have enabled us to test and revise our knowledge of the processes by comparing the predicted and observed values of the radical concentrations. We developed a laser-induced fluorescence (LIF) instrument and successfully observed OH and HO(2) at three remote islands of Japan (Oki Island, Okinawa Island, and Rishiri Island). At Okinawa Island, the observed daytime level of HO(2) agreed closely with the model estimates, suggesting that the photochemistry at Okinawa is well described by the current chemistry mechanism. At Rishiri Island, in contrast, the observed daytime level of HO(2) was consistently much lower than the calculated values. We proposed that iodine chemistr...
The Science of the total environment, Jan 15, 2014
Aerosol samples were collected in autumn 2007 on day- and nighttime basis in the northern recepto... more Aerosol samples were collected in autumn 2007 on day- and nighttime basis in the northern receptor site of Beijing, China. The samples were analyzed for total carbon (TC) and water-soluble dicarboxylic acids (C2-C12), oxocarboxylic acids (C2-C9), glyoxal and methylglyoxal to better understand the photochemical aging of organic aerosols in the vicinity of Beijing. Concentrations of TC are 50% greater in daytime when winds come from Beijing than in nighttime when winds come from the northern forest areas. Most diacids showed higher concentrations in daytime, suggesting that the organics emitted from the urban Beijing and delivered to the northern vicinity in daytime are subjected to photo-oxidation to result in diacids. However, oxalic acid (C2), which is the most abundant diacid followed by C3 or C4, became on average 30% more abundant in nighttime together with azelaic, ω-oxooctanoic and ω-oxononanoic acids, which are specific oxidation products of biogenic unsaturated fatty acids. ...
Journal of Atmospheric Chemistry, 2001
An instrument for measuringtropospheric OH/HO2 radicals by laser-inducedfluorescence developed in... more An instrument for measuringtropospheric OH/HO2 radicals by laser-inducedfluorescence developed in our laboratory is presentedin detail. It is based on FAGE (fluorescence assay bygas expansion) technique and OH is both excited anddetected at 308 nm corresponding to its A-X(0,0) band.The alignment of the laser beam, the design of thesample gas inlet, and the devices for the fluorescencedetection are optimized so as
Intra-Asian Air Pollutions and Their Transport: Characterization From Ground Based Observation
ABSTRACT
There have been a lot of documented cases of antipsychotic drug induced galactorrhea or non-puerp... more There have been a lot of documented cases of antipsychotic drug induced galactorrhea or non-puerperal lactation and isolated case reports of selective serotonin reuptake inhibitor induced galactorrhea. Here we are reporting a case of amitriptyline, a tricyclic antidepressant induced galactorrhea and complete resolution when the drug was withdrawn. There are other literature documenting antidepressant induced galactorrhea. This literature here is to support and understand the current trends and mechanism as it is different from what we encounter with antipsychotic.
Atmospheric Environment, 2015
h i g h l i g h t s NO 2 profile observations have been made by using MAX-DOAS at Fukuoka, an urb... more h i g h l i g h t s NO 2 profile observations have been made by using MAX-DOAS at Fukuoka, an urban area. NO 2 inhomogeneity is strongly related to transport associated with a landesea breeze. Observation by MAX-DOAS is a powerful tool for understanding of pollutant transport.
The Journal of Physical Chemistry A, 2008
The HO 2 uptake coefficient (γ) for inorganic submicrometer wet and dry aerosol particles ((NH 4)... more The HO 2 uptake coefficient (γ) for inorganic submicrometer wet and dry aerosol particles ((NH 4) 2 SO 4 and NaCl) under ambient conditions (760 Torr and 296 (2 K) was measured using an aerosol flow tube (AFT) coupled with a chemical conversion/laser-induced fluorescence (CC/LIF) technique. The CC/LIF technique enabled experiments to be performed at almost the same HO 2 radical concentration as that in the atmosphere. HO 2 radicals were injected into the AFT through a vertically movable Pyrex tube. Injector position-dependent profiles of LIF intensity were measured as a function of aerosol concentration. Measured γ values for dry aerosols of (NH 4) 2 SO 4 were 0.04 (0.02 and 0.05 (0.02 at 20% and 45% relative humidity (RH), respectively, while those of NaCl were <0.01 and 0.02 (0.01 at 20% and 53% RH, respectively. For wet (NH 4) 2 SO 4 aerosols, measured γ values were 0.11 (0.03, 0.15 (0.03, 0.17 (0.04, and 0.19 (0.04, at 45%, 55%, 65%, and 75% RH, respectively, whereas for wet NaCl aerosols the values were 0.11 (0.03, 0.09 (0.02, and 0.10 (0.02 for 53%, 63%, and 75% RH, respectively. Wet (NH 4) 2 SO 4 and NaCl aerosols doped with CuSO 4 showed γ values of 0.53 (0.12 and 0.65 (0.17, respectively. These results suggest that compositions, RH, and phase for aerosol particles are significant to HO 2 uptake. Potential HO 2 loss processes and their atmospheric contributions are discussed.
Tellus B, 2009
The summer of 2003 was an active forest fire season in Siberia. Several events of elevated carbon... more The summer of 2003 was an active forest fire season in Siberia. Several events of elevated carbon monoxide (CO) were observed at Rishiri Island in northern Japan during an intensive field campaign in September, 2003. A simulation with a global chemistry-transport model is able to reproduce the general features of the baseline levels and variability in the observed CO, and a source attribution for CO in the model suggests that the contribution from North Asia dominated, accounting for approximately 50% on average, with contributions of 7% from North America and 8% from Europe, and 30% from oxidation of hydrocarbons. With consideration of recent emission estimates for East Asian fossil fuel and Siberian biomass burning sources, the model captures the timing and magnitude of the CO enhancements in two pollution episodes well (September 17 and 24). However, it significantly underestimates the amplitude during another episode (September 11-13), requiring additional CO emissions for this event. Daily satellite images from AIRS reveal CO plumes transported from western Siberia toward northern Japan. These results suggest that CO emissions from biomass burning in western Siberia in 2003 are likely underestimated in the inventory, and further highlight large uncertainties in estimating trace gas emissions from boreal fires.
Diurnal variations in H2O2, O3, PAN, HNO3 and aldehyde concentrations and NO/NO2 ratios at Rishiri Island, Japan: Potential influence from iodine chemistry
Science of The Total Environment, 2007
The presence of iodine chemistry, hypothesized due to the overprediction of HO(2) levels by a pho... more The presence of iodine chemistry, hypothesized due to the overprediction of HO(2) levels by a photochemical box model at Rishiri Island in June 2000, was quantitatively tested against the observed NO/NO(2) ratios and the net production rates of ozone. The observed NO/NO(2) ratios were reproduced reasonably well by considering the conversion of NO to NO(2) by IO, whose amount was calculated so as to reproduce the observed HO(2) levels. However, the net production rates of ozone were calculated to be negative when such high mixing ratios of IO were considered, which was inconsistent with the observed buildup of ozone during daytime. These results suggest that iodine chemistry may not be the sole mechanism for the reduced mixing ratios of HO(2), or that &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;hot spots&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; for iodine chemistry were present. Diurnal variations in the mixing ratios of HCHO, CH(3)CHO, peroxy acetyl nitrate (PAN) and HNO(3) observed during the study are presented along with the simulated ones. The box model simulations suggest that the effect of iodine chemistry on these concentrations is small and that important sources of CH(3)CHO and sinks of PAN are probably missing from our current understanding of the tropospheric chemistry mechanism.
Journal of the Meteorological Society of Japan, 2010
Large amounts of reactive gases and aerosols are emitted from urban areas. Megacities, including ... more Large amounts of reactive gases and aerosols are emitted from urban areas. Megacities, including the Tokyo Metropolitan Area (TMA), are very large, concentrated sources of these species a¤ecting local, regional, and global ozone (O 3) and aerosol levels. Emissions strongly influence air quality and climate on these scales. In 2003-2004, we made intensive measurements of O 3 and chemical composition of aerosol particles with diameters less than 1 mm (PM 1 aerosol) together with their precursors for the first time in Tokyo, Japan, as a part of the series of Integrated Measurement Program for Aerosol and Oxidant Chemistry in Tokyo (IMPACT) campaigns. Using these data, we investigated the formation and transport processes of O 3 and PM 1 aerosols through the analysis of their temporal variations near the urban center of Tokyo and regions downwind. Key findings obtained in these studies are reviewed in this paper.
The Journal of Physical Chemistry Letters, 2010
The uptake coefficient(γ) of HO 2 for submicrometer aerosol particles of levoglucosan and polysty... more The uptake coefficient(γ) of HO 2 for submicrometer aerosol particles of levoglucosan and polystyrene latex (PSL) under ambient conditions (760 Torr and 296 (2 K) have been investigated using an aerosol flow tube (AFT) coupled with a chemical conversion/laser-induced fluorescence (CC/LIF) technique. Determined γ values for levoglucosan particles were <0.01, 0.01 (0.01, 0.05 (0.01, 0.09 (0.02, and 0.13 (0.03, at relative humidities (RHs) of 20, 40, 55, 75, and 92%, respectively, while the γ values for PSL particles were 0.01 (0.01, 0.02 (0.01, and 0.03 (0.01 at RHs of 22, 58, and 92%, respectively. The dependence of HO 2 uptake on RH by levoglucosan and PSL particles is discussed. SECTION Atmospheric, Environmental and Green Chemistry
Journal of Geophysical Research, 2008
Total suspended particles (TSP) were collected at the summit of Mt. Tai (1534 m above sea level) ... more Total suspended particles (TSP) were collected at the summit of Mt. Tai (1534 m above sea level) on a daytime and nighttime basis during a summertime campaign (May-June 2006) and were characterized for organic molecular compositions using solvent extraction/derivatization and gas chromatography/mass spectrometry technique. The n-Alkanes, fatty acids, fatty alcohols, sugars, glycerol and polyacids, and phthalate esters were found as major organic compound classes, whereas lignin and resin products, sterols, aromatic acids, hopanes, and polycyclic aromatic hydrocarbons (PAHs) were detected as minor classes. Sugars (49.8-2115 ng m À3 , average 640 ng m À3 in daytime; 18.1-4348 ng m À3 , 799 ng m À3 in nighttime) were found to be the dominant compound class. Levoglucosan, a specific cellulose pyrolysis product, was detected as the most abundant single compound, followed by C 28 fatty alcohol, diisobutyl and din -butyl phthalates, C 29 n-alkane, C 16 and C 28 fatty acids, and malic acid. By grouping organic compounds based on their sources, we found that emission of terrestrial plant waxes was the most significant source (30-34%) of the TSP, followed by biomass burning products (25-27%) (e.g., levoglucosan and lignin and resin products), soil resuspension (15-18%) due to agricultural activities, secondary oxidation products (8-10%), plastic emission (3-10%), marine/microbial sources (6%), and urban/industrial emissions from fossil fuel use (4%). However, low molecular weight dicarboxylic acids (such as oxalic acid) of photochemical origin were not included in this study. Malic acid was found to be much higher than those reported in the ground level, suggesting an enhanced photochemical production in the free troposphere over mountain areas. Temporal variations of biomass burning tracers (e.g., levoglucosan, galactosan, mannosan) and some higher plant wax derived compound classes suggested that there were two major (E1 and E2) and one minor (E3) biomass-burning events during this campaign. Most of the compound classes showed higher concentrations in nighttime samples when organic aerosols can be long-range transported from different source regions to the summit of Mt. Tai above the planetary boundary layer (PBL). This study also demonstrates that the free troposphere over Mt. Tai is heavily influenced by field burning of agricultural wastes such as wheat straws in the North China Plain during the harvest season in early summer.
Journal of Geophysical Research, 2007
The Rishiri Fall Experiment (RISFEX) was performed in September 2003 at a remote coastal site (45... more The Rishiri Fall Experiment (RISFEX) was performed in September 2003 at a remote coastal site (45.07°N, 141.12°E, and 35 m asl) on Rishiri Island in the Sea of Japan. Peroxy radicals were measured from 15-21 September using a peroxy radical chemical amplifier (PERCA) instrument. Simultaneously measured were O 3 , NO, NO 2 , CO, nonmethane hydrocarbons (NMHCs), biogenic volatile organic compounds (BVOCs), carbonyl compounds, aromatics, volatile organoiodines, organobromines, black carbon, aerosols and photolysis frequencies of j(O 1 D) and j(NO 2) as well as meteorological parameters. The data set covers the measurements under relative background conditions and polluted episodes over the period. The midday 30-min averages of peroxy radicals ranged from 10 to 40 pptv with the highest observed on the event when the air masses were transported over the polluted continent in northern China before reaching the site. The significant radical signals were observed repeatedly in the early morning and late afternoon when j(O 1 D) was greatly reduced, resulting in the diurnal cycles of peroxy radicals much broader than those expected from the photolysis of O 3 alone. A box model based on RACM (Regional Atmospheric Chemistry Mechanism) was used to calculate OH, HO 2 and RO 2 concentrations from measured stable species and parameters. The calculated peroxy radical concentrations agree well with measured ones during 0900-1530 Japan Standard Time (JST) (JST = UT + 9 hours) from 19 to 21 September. However, in the early morning and later afternoon when monoterpenes were the dominant VOC, the model overpredicts peroxy radicals by up to 85%. The including of uptake of radicals to aerosols into the model cannot account for the discrepancy. An underprediction by the model up to 45% was observed during noon hours on 18 September when isoprene concentration was high. It appears that unknown terpenes are present, which might produce extra radicals beyond the predicted by the model. The measured-tomodeled ratio of peroxy radical concentrations is near unity for [NO] < 120 pptv, but rises up to 15 for [NO] > 120 pptv, suggesting the presence of an unknown radical production process which is related with high NO concentration.
Journal of Geophysical Research, 2007
We used laser-induced fluorescence to measure the concentrations of OH and HO 2 radicals in centr... more We used laser-induced fluorescence to measure the concentrations of OH and HO 2 radicals in central Tokyo during two intensive campaigns (IMPACT IVand IMPACT L) in January-February and July-August 2004. The estimated detection limit for the 10-min data was 1.3 Â 10 5 cm À3 for the nighttime and 5.2 Â 10 5 cm À3 for the daytime. The median values of the daytime peak concentrations of HO 2 were 1.1 and 5.7 pptv for the winter and summer periods, respectively, while the values for OH were 1.5 Â 10 6 and 6.3 Â 10 6 cm À3. High HO 2 mixing ratios (>50 pptv) were observed on a day in summer when O 3 mixing ratios exceeded 100 ppbv. The average nighttime concentrations of HO 2 were 0.7 and 2.6 pptv for the winter and summer periods, respectively, while the values for OH were 1.8 Â 10 5 and 3.7 Â 10 5 cm À3. A photochemical box model constrained by ancillary observations was able to reproduce daytime OH concentrations reasonably well for both periods, although daytime HO 2 concentrations were underestimated in winter and overestimated in summer. Increasing the wintertime hydrocarbon concentrations in the model led to an increase in daytime HO 2 concentrations, thereby showing better agreement with observations; however, the model continued to underestimate HO 2 concentrations at high NO mixing ratios. This underestimate was most pronounced in the mornings of both periods and during the daytime in winter. We studied processes that are capable of explaining this discrepancy, including unknown reactions of HNO 4 or an unidentified HO x source that is linearly scalable to the NO mixing ratio. The important processes in terms of producing radicals were the olefin + O 3 reactions in the nighttime of both periods and during the daytime in winter, the photolysis of carbonyls in the daytime for both periods, and the photolysis of HONO during the daytime in winter (using measured HONO concentrations) and during mornings in summer (using estimated HONO concentrations).
Atmospheric Chemistry and Physics, 2009
An observation-based box model approach was undertaken to estimate concentrations of OH, HO 2 , a... more An observation-based box model approach was undertaken to estimate concentrations of OH, HO 2 , and RO 2 radicals and the net photochemical production rate of ozone at the top of Mount Tai, located in the middle of Central East China, in June 2006. The model calculation was constrained by the measurements of O 3 , H 2 O, CO, NO, NO 2 , hydrocarbon, HCHO, and CH 3 CHO concentrations, and temperature and J values. The net production rate of ozone was estimated to be 6.4 ppb h −1 as a 6-h average (09:00-15:00 CST), suggesting 58±37 ppb of ozone is produced in one day. Thus the daytime buildup of ozone recorded at the mountain top as ∼23 ppb on average is likely affected by in situ photochemistry as well as by the upward transport of polluted air mass in the daytime. On days with high ozone concentrations (hourly values exceeding 100 ppb at least once), in situ photochemistry was more active than it was on low ozone days, suggesting that in situ photochemistry is an important factor controlling ozone concentrations. Sensitivity model runs for which different NO x and hydrocarbon concentrations were assumed suggested that the ozone production occurred normally under NO x-limited conditions, with some exceptional periods (under volatile-organic-compound-limited conditions) in which there was fresh pollution. We also examined the possible influence of the heterogeneous loss of gaseous HO 2 radicals in contact with aerosol particle surfaces on the rate and regimes of ozone production.
Atmospheric Chemistry and Physics Discussions, 2013
Aerosol samples (TSP, n = 58) were collected on day-and night-time basis at Mangshan in the north... more Aerosol samples (TSP, n = 58) were collected on day-and night-time basis at Mangshan in the north of Beijing, China in autumn 2007 to better understand the status of air quality and the influence of urban pollutants in the northern vicinity of Beijing. The samples were analyzed for aerosol mass, total carbon (TC), low molecular weight α, ω-dicarboxylic acids (C 2-C 12), ketoacids (ωC 2-ωC 9 , pyruvic acid), αdicarbonyls (glyoxal and methylglyoxal), as well as aromatic (phthalic, iso-and terephthalic) diacids. Aerosol mass and TC concentrations are higher in daytime than in nighttime. TC/aerosol mass ratios in this study are lower than those reported in megacities in East Asia, but higher than those reported in marine aerosols. Molecular distributions of diacids demonstrated that oxalic (C 2) acid was the most abundant species, comprising 38-77 % of total diacids, followed by succinic (C 4) and malonic (C 3) acids. For most compounds, the concentrations were higher in daytime than nighttime, indicating that diacids are produced in daytime by photochemical oxidation of organic precursors emitted from anthropogenic sources in Beijing during the transport to Mangshan area by the northward wind. However, we found that C 2 concentrations are higher in nighttime than in daytime. A positive correlation of C 2 to glyoxylic acid (ωC 2) was obtained at night when relative humidity increased up to 100 %, suggesting that aqueous phase production of C 2 occurs in nighttime via the oxidation of ωC 2. Depletion of C 2 by photolysis of Fe-oxalato complexes might be another reason for the lower concentrations of C 2 in daytime samples. High phthalic acid/C 4 ratios in the aerosol samples suggest that automobile combustion and coal burning products are important sources, which are subjected to photochemical oxidation during the atmospheric transport of urban aerosols from Beijing. In contrast, higher concentrations of methylglyoxal in nighttime than daytime may suggest that isoprene emitted from the northern forest area is oxidized in daytime and then transported to the sampling area at night by northerly winds. This study demonstrates that secondary organic aerosols are significantly produced and aged in the vicinity of Beijing during atmospheric transport.
Journal of Geophysical Research: Atmospheres, 2015
The emission factors (EFs) of non-methane volatile organic compounds (NMVOCs) emitted during the ... more The emission factors (EFs) of non-methane volatile organic compounds (NMVOCs) emitted during the burning of Chinese crop residue were investigated as a function of modified combustion efficiency (MCE) in laboratory experiments. NMVOCs, including acetonitrile, aldehydes/ketones, furan, and aromatic hydrocarbons, were monitored by proton-transfer-reaction mass spectrometry (PTR-MS). Rape plant was burned in dry conditions and wheat straw was burned in both wet and dry conditions to simulate the possible burning of damp crop residue in regions of high temperature and humidity. We compared the present data to field data reported by Kudo et al [2014] Good agreement between field and laboratory data was obtained for aromatics under
Diurnal variations of carbonaceous components, major ions, and stable carbon and nitrogen isotope ratios in suburban aerosols from northern vicinity of Beijing
Atmospheric Environment, 2015
Abstract We report diurnal variations of organic carbon (OC), elemental carbon (EC), water-solubl... more Abstract We report diurnal variations of organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and major ions as well as stable carbon and nitrogen isotope ratios (δ 13 C and δ 15 N) in ambient aerosols at a suburban site (Mangshan), 40 km north of Beijing, China. We found that aerosol chemical compositions were largely controlled by the air mass transport from Beijing in daytime with southerly winds and by relatively fresh air mass in nighttime from the northern forest areas with northerly winds. Higher concentrations of aerosol mass and total carbon were obtained in daytime. Further, higher OC/EC ratios were recorded in daytime (4.0 ± 1.7) than nighttime (3.2 ± 0.7), suggesting that OC is formed by photochemical oxidation of gaseous precursors in daytime. Contributions of WSOC to OC were slightly higher in daytime (38%) than nighttime (34%), possibly due to secondary formation of WSOC in daytime. We also found higher concentrations of Ca 2+ in daytime, which was originated from the construction dust in Beijing area and transported to the sampling site. δ 13 C ranged from −25.3 to −21.2‰ (ave. −23.5 ± 0.9‰) in daytime and −29.0 to −21.4‰ (−24.0 ± 1.5‰) in nighttime, suggesting that Mangshan aerosols were more influenced by fossil fuel combustion products in daytime and by terrestrial C 3 plants in nighttime. This study suggests that daytime air mass delivery from megacity Beijing largely influence the air quality at the receptor site in the north together with photochemical processing of organic aerosols during the atmospheric transport, whereas the Mangshan site is covered with relatively clean air masses at night.
Journal of Geophysical Research: Atmospheres, 2014
Open crop residue burning is one of the major sources of air pollutants including the precursors ... more Open crop residue burning is one of the major sources of air pollutants including the precursors of photooxidants like ozone and secondary organic aerosol. We made measurements of trace gases including nonmethane volatile organic compounds (NMVOCs) in a rural area in central East China in June 2010. During the campaign, we identified six biomass burning events in total through the simultaneous enhancement of carbon monoxide and acetonitrile. Four cases represented fresh plumes (<2 h after emission), and two cases represented aged plumes (>3 h after emission), as determined by photochemical age. While we were not able to quantify formic acid, we identified an enhancement of major oxygenated volatile organic compounds (OVOCs) as well as low molecular alkanes and alkenes, and aromatic hydrocarbons in these plumes. The observed normalized excess mixing ratios (NEMRs) of OVOCs and alkenes showed dependence on air mass age, even in fresh smoke plumes, supporting the view that these species are rapidly produced and destructed, respectively, during plume evolution. Based on the NEMR data in the fresh plumes, we calculated the emission factors (EFs) of individual NMVOC. The comparison to previous reports suggests that the EFs of formaldehyde and acetic acid have been overestimated, while those of alkenes have been underestimated. Finally, we suggest that open burning of wheat residue in China releases about 0.34 Tg NMVOCs annually. If we applied the same EFs to all crops, the annual NMVOC emissions would be 2.33 Tg. The EFs of speciated NMVOCs can be used to improve the existing inventories.
GEOCHEMICAL JOURNAL, 2015
by chemical reactions involving precursor gases such as SO 2 , NO X , and volatile organic compou... more by chemical reactions involving precursor gases such as SO 2 , NO X , and volatile organic compounds in the atmosphere. PM 2.5 is derived from anthropogenic or natural sources including fuel combustion in power plants and transport, biomass burning, vegetation, volcanoes, and dust. In Japan, an environmental standard for PM 2.5 was newly established in September 2009, with an annual mean value of 15 mg m-3 and a daily mean value of 35 mg m-3. Since then, the number of monitoring sites for PM 2.5 has been increased by the Japanese Ministry of the Environment (MOE) to understand the status of PM 2.5 pollution over Japan. Observations made by the MOE have indicated that an achievement ratio of the environmental standard determined at the ambient monitoring stations is about 30% for the fiscal years 2010 and 2011 (http:// www.env.go.jp/air/osen/jokyo_h23/index.html). The monitoring stations at which PM 2.5 mass concentrations exceed the environmental standard are concentrated in the western part of Japan. In addition, Kanaya et al. (2010) reported that the PM 2.5 concentration at Fukue Island,
Direct measurements of HOx radicals in the marine boundary layer: testing the current tropospheric chemistry mechanism
Chemical record (New York, N.Y.), 2002
OH and HO(2) radicals, atmospheric detergents, and the reservoir thereof, play central roles in t... more OH and HO(2) radicals, atmospheric detergents, and the reservoir thereof, play central roles in tropospheric chemistry. In spite of their importance, we had no choice but to trust their concentrations predicted by modeling studies based on known chemical processes. However, recent direct measurements of these radicals have enabled us to test and revise our knowledge of the processes by comparing the predicted and observed values of the radical concentrations. We developed a laser-induced fluorescence (LIF) instrument and successfully observed OH and HO(2) at three remote islands of Japan (Oki Island, Okinawa Island, and Rishiri Island). At Okinawa Island, the observed daytime level of HO(2) agreed closely with the model estimates, suggesting that the photochemistry at Okinawa is well described by the current chemistry mechanism. At Rishiri Island, in contrast, the observed daytime level of HO(2) was consistently much lower than the calculated values. We proposed that iodine chemistr...
The Science of the total environment, Jan 15, 2014
Aerosol samples were collected in autumn 2007 on day- and nighttime basis in the northern recepto... more Aerosol samples were collected in autumn 2007 on day- and nighttime basis in the northern receptor site of Beijing, China. The samples were analyzed for total carbon (TC) and water-soluble dicarboxylic acids (C2-C12), oxocarboxylic acids (C2-C9), glyoxal and methylglyoxal to better understand the photochemical aging of organic aerosols in the vicinity of Beijing. Concentrations of TC are 50% greater in daytime when winds come from Beijing than in nighttime when winds come from the northern forest areas. Most diacids showed higher concentrations in daytime, suggesting that the organics emitted from the urban Beijing and delivered to the northern vicinity in daytime are subjected to photo-oxidation to result in diacids. However, oxalic acid (C2), which is the most abundant diacid followed by C3 or C4, became on average 30% more abundant in nighttime together with azelaic, ω-oxooctanoic and ω-oxononanoic acids, which are specific oxidation products of biogenic unsaturated fatty acids. ...
Journal of Atmospheric Chemistry, 2001
An instrument for measuringtropospheric OH/HO2 radicals by laser-inducedfluorescence developed in... more An instrument for measuringtropospheric OH/HO2 radicals by laser-inducedfluorescence developed in our laboratory is presentedin detail. It is based on FAGE (fluorescence assay bygas expansion) technique and OH is both excited anddetected at 308 nm corresponding to its A-X(0,0) band.The alignment of the laser beam, the design of thesample gas inlet, and the devices for the fluorescencedetection are optimized so as
Intra-Asian Air Pollutions and Their Transport: Characterization From Ground Based Observation
ABSTRACT
There have been a lot of documented cases of antipsychotic drug induced galactorrhea or non-puerp... more There have been a lot of documented cases of antipsychotic drug induced galactorrhea or non-puerperal lactation and isolated case reports of selective serotonin reuptake inhibitor induced galactorrhea. Here we are reporting a case of amitriptyline, a tricyclic antidepressant induced galactorrhea and complete resolution when the drug was withdrawn. There are other literature documenting antidepressant induced galactorrhea. This literature here is to support and understand the current trends and mechanism as it is different from what we encounter with antipsychotic.
Atmospheric Environment, 2015
h i g h l i g h t s NO 2 profile observations have been made by using MAX-DOAS at Fukuoka, an urb... more h i g h l i g h t s NO 2 profile observations have been made by using MAX-DOAS at Fukuoka, an urban area. NO 2 inhomogeneity is strongly related to transport associated with a landesea breeze. Observation by MAX-DOAS is a powerful tool for understanding of pollutant transport.
The Journal of Physical Chemistry A, 2008
The HO 2 uptake coefficient (γ) for inorganic submicrometer wet and dry aerosol particles ((NH 4)... more The HO 2 uptake coefficient (γ) for inorganic submicrometer wet and dry aerosol particles ((NH 4) 2 SO 4 and NaCl) under ambient conditions (760 Torr and 296 (2 K) was measured using an aerosol flow tube (AFT) coupled with a chemical conversion/laser-induced fluorescence (CC/LIF) technique. The CC/LIF technique enabled experiments to be performed at almost the same HO 2 radical concentration as that in the atmosphere. HO 2 radicals were injected into the AFT through a vertically movable Pyrex tube. Injector position-dependent profiles of LIF intensity were measured as a function of aerosol concentration. Measured γ values for dry aerosols of (NH 4) 2 SO 4 were 0.04 (0.02 and 0.05 (0.02 at 20% and 45% relative humidity (RH), respectively, while those of NaCl were <0.01 and 0.02 (0.01 at 20% and 53% RH, respectively. For wet (NH 4) 2 SO 4 aerosols, measured γ values were 0.11 (0.03, 0.15 (0.03, 0.17 (0.04, and 0.19 (0.04, at 45%, 55%, 65%, and 75% RH, respectively, whereas for wet NaCl aerosols the values were 0.11 (0.03, 0.09 (0.02, and 0.10 (0.02 for 53%, 63%, and 75% RH, respectively. Wet (NH 4) 2 SO 4 and NaCl aerosols doped with CuSO 4 showed γ values of 0.53 (0.12 and 0.65 (0.17, respectively. These results suggest that compositions, RH, and phase for aerosol particles are significant to HO 2 uptake. Potential HO 2 loss processes and their atmospheric contributions are discussed.
Tellus B, 2009
The summer of 2003 was an active forest fire season in Siberia. Several events of elevated carbon... more The summer of 2003 was an active forest fire season in Siberia. Several events of elevated carbon monoxide (CO) were observed at Rishiri Island in northern Japan during an intensive field campaign in September, 2003. A simulation with a global chemistry-transport model is able to reproduce the general features of the baseline levels and variability in the observed CO, and a source attribution for CO in the model suggests that the contribution from North Asia dominated, accounting for approximately 50% on average, with contributions of 7% from North America and 8% from Europe, and 30% from oxidation of hydrocarbons. With consideration of recent emission estimates for East Asian fossil fuel and Siberian biomass burning sources, the model captures the timing and magnitude of the CO enhancements in two pollution episodes well (September 17 and 24). However, it significantly underestimates the amplitude during another episode (September 11-13), requiring additional CO emissions for this event. Daily satellite images from AIRS reveal CO plumes transported from western Siberia toward northern Japan. These results suggest that CO emissions from biomass burning in western Siberia in 2003 are likely underestimated in the inventory, and further highlight large uncertainties in estimating trace gas emissions from boreal fires.
Diurnal variations in H2O2, O3, PAN, HNO3 and aldehyde concentrations and NO/NO2 ratios at Rishiri Island, Japan: Potential influence from iodine chemistry
Science of The Total Environment, 2007
The presence of iodine chemistry, hypothesized due to the overprediction of HO(2) levels by a pho... more The presence of iodine chemistry, hypothesized due to the overprediction of HO(2) levels by a photochemical box model at Rishiri Island in June 2000, was quantitatively tested against the observed NO/NO(2) ratios and the net production rates of ozone. The observed NO/NO(2) ratios were reproduced reasonably well by considering the conversion of NO to NO(2) by IO, whose amount was calculated so as to reproduce the observed HO(2) levels. However, the net production rates of ozone were calculated to be negative when such high mixing ratios of IO were considered, which was inconsistent with the observed buildup of ozone during daytime. These results suggest that iodine chemistry may not be the sole mechanism for the reduced mixing ratios of HO(2), or that &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;hot spots&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; for iodine chemistry were present. Diurnal variations in the mixing ratios of HCHO, CH(3)CHO, peroxy acetyl nitrate (PAN) and HNO(3) observed during the study are presented along with the simulated ones. The box model simulations suggest that the effect of iodine chemistry on these concentrations is small and that important sources of CH(3)CHO and sinks of PAN are probably missing from our current understanding of the tropospheric chemistry mechanism.
Journal of the Meteorological Society of Japan, 2010
Large amounts of reactive gases and aerosols are emitted from urban areas. Megacities, including ... more Large amounts of reactive gases and aerosols are emitted from urban areas. Megacities, including the Tokyo Metropolitan Area (TMA), are very large, concentrated sources of these species a¤ecting local, regional, and global ozone (O 3) and aerosol levels. Emissions strongly influence air quality and climate on these scales. In 2003-2004, we made intensive measurements of O 3 and chemical composition of aerosol particles with diameters less than 1 mm (PM 1 aerosol) together with their precursors for the first time in Tokyo, Japan, as a part of the series of Integrated Measurement Program for Aerosol and Oxidant Chemistry in Tokyo (IMPACT) campaigns. Using these data, we investigated the formation and transport processes of O 3 and PM 1 aerosols through the analysis of their temporal variations near the urban center of Tokyo and regions downwind. Key findings obtained in these studies are reviewed in this paper.
The Journal of Physical Chemistry Letters, 2010
The uptake coefficient(γ) of HO 2 for submicrometer aerosol particles of levoglucosan and polysty... more The uptake coefficient(γ) of HO 2 for submicrometer aerosol particles of levoglucosan and polystyrene latex (PSL) under ambient conditions (760 Torr and 296 (2 K) have been investigated using an aerosol flow tube (AFT) coupled with a chemical conversion/laser-induced fluorescence (CC/LIF) technique. Determined γ values for levoglucosan particles were <0.01, 0.01 (0.01, 0.05 (0.01, 0.09 (0.02, and 0.13 (0.03, at relative humidities (RHs) of 20, 40, 55, 75, and 92%, respectively, while the γ values for PSL particles were 0.01 (0.01, 0.02 (0.01, and 0.03 (0.01 at RHs of 22, 58, and 92%, respectively. The dependence of HO 2 uptake on RH by levoglucosan and PSL particles is discussed. SECTION Atmospheric, Environmental and Green Chemistry
Journal of Geophysical Research, 2008
Total suspended particles (TSP) were collected at the summit of Mt. Tai (1534 m above sea level) ... more Total suspended particles (TSP) were collected at the summit of Mt. Tai (1534 m above sea level) on a daytime and nighttime basis during a summertime campaign (May-June 2006) and were characterized for organic molecular compositions using solvent extraction/derivatization and gas chromatography/mass spectrometry technique. The n-Alkanes, fatty acids, fatty alcohols, sugars, glycerol and polyacids, and phthalate esters were found as major organic compound classes, whereas lignin and resin products, sterols, aromatic acids, hopanes, and polycyclic aromatic hydrocarbons (PAHs) were detected as minor classes. Sugars (49.8-2115 ng m À3 , average 640 ng m À3 in daytime; 18.1-4348 ng m À3 , 799 ng m À3 in nighttime) were found to be the dominant compound class. Levoglucosan, a specific cellulose pyrolysis product, was detected as the most abundant single compound, followed by C 28 fatty alcohol, diisobutyl and din -butyl phthalates, C 29 n-alkane, C 16 and C 28 fatty acids, and malic acid. By grouping organic compounds based on their sources, we found that emission of terrestrial plant waxes was the most significant source (30-34%) of the TSP, followed by biomass burning products (25-27%) (e.g., levoglucosan and lignin and resin products), soil resuspension (15-18%) due to agricultural activities, secondary oxidation products (8-10%), plastic emission (3-10%), marine/microbial sources (6%), and urban/industrial emissions from fossil fuel use (4%). However, low molecular weight dicarboxylic acids (such as oxalic acid) of photochemical origin were not included in this study. Malic acid was found to be much higher than those reported in the ground level, suggesting an enhanced photochemical production in the free troposphere over mountain areas. Temporal variations of biomass burning tracers (e.g., levoglucosan, galactosan, mannosan) and some higher plant wax derived compound classes suggested that there were two major (E1 and E2) and one minor (E3) biomass-burning events during this campaign. Most of the compound classes showed higher concentrations in nighttime samples when organic aerosols can be long-range transported from different source regions to the summit of Mt. Tai above the planetary boundary layer (PBL). This study also demonstrates that the free troposphere over Mt. Tai is heavily influenced by field burning of agricultural wastes such as wheat straws in the North China Plain during the harvest season in early summer.
Journal of Geophysical Research, 2007
The Rishiri Fall Experiment (RISFEX) was performed in September 2003 at a remote coastal site (45... more The Rishiri Fall Experiment (RISFEX) was performed in September 2003 at a remote coastal site (45.07°N, 141.12°E, and 35 m asl) on Rishiri Island in the Sea of Japan. Peroxy radicals were measured from 15-21 September using a peroxy radical chemical amplifier (PERCA) instrument. Simultaneously measured were O 3 , NO, NO 2 , CO, nonmethane hydrocarbons (NMHCs), biogenic volatile organic compounds (BVOCs), carbonyl compounds, aromatics, volatile organoiodines, organobromines, black carbon, aerosols and photolysis frequencies of j(O 1 D) and j(NO 2) as well as meteorological parameters. The data set covers the measurements under relative background conditions and polluted episodes over the period. The midday 30-min averages of peroxy radicals ranged from 10 to 40 pptv with the highest observed on the event when the air masses were transported over the polluted continent in northern China before reaching the site. The significant radical signals were observed repeatedly in the early morning and late afternoon when j(O 1 D) was greatly reduced, resulting in the diurnal cycles of peroxy radicals much broader than those expected from the photolysis of O 3 alone. A box model based on RACM (Regional Atmospheric Chemistry Mechanism) was used to calculate OH, HO 2 and RO 2 concentrations from measured stable species and parameters. The calculated peroxy radical concentrations agree well with measured ones during 0900-1530 Japan Standard Time (JST) (JST = UT + 9 hours) from 19 to 21 September. However, in the early morning and later afternoon when monoterpenes were the dominant VOC, the model overpredicts peroxy radicals by up to 85%. The including of uptake of radicals to aerosols into the model cannot account for the discrepancy. An underprediction by the model up to 45% was observed during noon hours on 18 September when isoprene concentration was high. It appears that unknown terpenes are present, which might produce extra radicals beyond the predicted by the model. The measured-tomodeled ratio of peroxy radical concentrations is near unity for [NO] < 120 pptv, but rises up to 15 for [NO] > 120 pptv, suggesting the presence of an unknown radical production process which is related with high NO concentration.
Journal of Geophysical Research, 2007
We used laser-induced fluorescence to measure the concentrations of OH and HO 2 radicals in centr... more We used laser-induced fluorescence to measure the concentrations of OH and HO 2 radicals in central Tokyo during two intensive campaigns (IMPACT IVand IMPACT L) in January-February and July-August 2004. The estimated detection limit for the 10-min data was 1.3 Â 10 5 cm À3 for the nighttime and 5.2 Â 10 5 cm À3 for the daytime. The median values of the daytime peak concentrations of HO 2 were 1.1 and 5.7 pptv for the winter and summer periods, respectively, while the values for OH were 1.5 Â 10 6 and 6.3 Â 10 6 cm À3. High HO 2 mixing ratios (>50 pptv) were observed on a day in summer when O 3 mixing ratios exceeded 100 ppbv. The average nighttime concentrations of HO 2 were 0.7 and 2.6 pptv for the winter and summer periods, respectively, while the values for OH were 1.8 Â 10 5 and 3.7 Â 10 5 cm À3. A photochemical box model constrained by ancillary observations was able to reproduce daytime OH concentrations reasonably well for both periods, although daytime HO 2 concentrations were underestimated in winter and overestimated in summer. Increasing the wintertime hydrocarbon concentrations in the model led to an increase in daytime HO 2 concentrations, thereby showing better agreement with observations; however, the model continued to underestimate HO 2 concentrations at high NO mixing ratios. This underestimate was most pronounced in the mornings of both periods and during the daytime in winter. We studied processes that are capable of explaining this discrepancy, including unknown reactions of HNO 4 or an unidentified HO x source that is linearly scalable to the NO mixing ratio. The important processes in terms of producing radicals were the olefin + O 3 reactions in the nighttime of both periods and during the daytime in winter, the photolysis of carbonyls in the daytime for both periods, and the photolysis of HONO during the daytime in winter (using measured HONO concentrations) and during mornings in summer (using estimated HONO concentrations).