Source Contributions to Carbon Monoxide Concentrations During KORUS‐AQ Based on CAM‐chem Model Applications

We investigate regional sources contributing to CO during the Korea United States Air Quality (KORUS-AQ) campaign conducted over Korea (1 May to 10 June 2016) using 17 tagged CO simulations from the Community Atmosphere Model with chemistry (CAM-chem). The simulations use three spatial resolutions, three anthropogenic emission inventories, two meteorological fields, and nine emission scenarios. These simulations are evaluated against measurements from the DC-8 aircraft and Measurements Of Pollution In The Troposphere (MOPITT). Results show that simulations using bottom-up emissions are consistently lower (bias: -34 to -39%) and poorer performing (Taylor skill: 0.38-0.61) than simulations using alternative anthropogenic emissions (bias: -6 to -33%; Taylor skill: 0.48-0.86), particularly for enhanced Asian CO and volatile organic compound (VOC) emission scenarios, suggesting underestimation in modeled CO background and emissions in the region. The ranges of source contributions to modeled CO along DC-8 aircraft from Korea and southern (90 degrees E to 123 degrees E, 20 degrees N to 29 degrees N), middle (90 degrees E to 123 degrees E, 29 degrees N to 38.5 degrees N), and northern (90 degrees E to 131.5 degrees E, 38.5 degrees N to 45 degrees N) East Asia (EA) are 6-13%, similar to 5%, 16-28%, and 9-18%, respectively. CO emissions from middle and northern EA can reach Korea via transport within the boundary layer, whereas those from southern EA are transported to Korea mainly through the free troposphere. Emission contributions from middle EA dominate during continental outflow events (29-51%), while Korean emissions play an overall more important role for ground sites (up to 25-49%) and plumes within the boundary layer (up to 25-44%) in Korea. Finally, comparisons with four other source contribution approaches (FLEXPART 9.1 back trajectory calculations driven by Weather Research and Forecasting (WRF) WRF inert tracer, China signature VOCs, and CO to CO2 enhancement ratios) show general consistency with CAM-chem.National Science Foundation (NSF); U.S. Department of Energy (DOE); National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) Program; NCAR Advanced Study Program Postdoctoral Fellowship; Environment Research and Technology Development Fund of the Ministry of the Environment, Japan [2-1505, 2-1803]; National Science Foundation; NASA [NNX16AD96G, NNX16AE16G, NNX17AG39G]6 month embargo; published online: 1 February 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

OH reactivity in urban and suburban regions in Seoul, South Korea – an East Asian megacity in a rapid transition

South Korea has recently achieved developed country status with the second largest megacity in the world, the Seoul Metropolitan Area (SMA). This study provides insights into future changes in air quality for rapidly emerging megacities in the East Asian region. We present total OH reactivity observations in the SMA conducted at an urban Seoul site (May-June, 2015) and a suburban forest site (Sep, 2015). The total OH reactivity in an urban site during the daytime was observed at similar levels (∼15 s(-1)) to those previously reported from other East Asian megacity studies. Trace gas observations indicate that OH reactivity is largely accounted for by NOX (∼50%) followed by volatile organic compounds (VOCs) (∼35%). Isoprene accounts for a substantial fraction of OH reactivity among the comprehensive VOC observational dataset (25-47%). In general, observed total OH reactivity can be accounted for by the observed trace gas dataset. However, observed total OH reactivity in the suburban forest area cannot be largely accounted for (∼70%) by the trace gas measurements. The importance of biogenic VOC (BVOCs) emissions and oxidations used to evaluate the impacts of East Asian megacity outflows for the regional air quality and climate contexts are highlighted in this study

Enhanced concentrations of citric acid in spring aerosols collected at the Gosan background site in East Asia

Elevated concentrations of atmospheric citric acid (range: 20-320 ng m^[-3]) were observed in total suspended particles collected at Gosan background site in Jeju Island, Korea during mid- to late April of 2007 and 2008. In order to specify the sources of citric acid, water-soluble dicarboxylic acids and related compounds were measured in the pollen sample collected at the Gosan site (Pollen_Gosan), authentic pollen samples from Japanese cedar (Pollen_cedar) and Japanese cypress trees (Pollen_cypress), and tangerine fruit produced from Jeju Island. Citric acid (2790 ng in unit mg of pollen mass) was found as most abundant species in the Pollen_Gosan, followed by oxalic acid (2390 ng mg^[-1]). Although citric acid was not detected in the Pollen_cedar and Pollen_cypress as major species, it was detected in the tangerine juice as a dominant species while malic acid was detected as major species in the tangerine peel, followed by oxalic and citric acids. Since Japanese cedar trees are planted around tangerine farms to prevent strong winds from the Pacific Ocean, citric acid that may be directly emitted from tangerine is likely adsorbed on pollens emitted from Japanese cedar and then transported to the Gosan site. Much lower malic/citric acid ratios under cloudy condition than clear condition suggest that malic acid may rapidly decompose to lower molecular weight compounds such as oxalic and malonic acids (<C4) via aqueous phase reaction in cloud during the atmospheric transport

Hygroscopic properties of particles nebulized from water extracts of aerosols collected at Chichijima Island in the western North Pacific: An outflow region of Asian dust

We present 2 year measurements of hygroscopic properties of water-soluble matter (WSM) extracted from marine aerosols from remote Chichijima Island in the western North Pacific during 2001-2002. Hygroscopic growth factors (g) of WSM were measured by a hygroscopicity tandem differential mobility analyzer with initial dry particle diameter of 100 nm. The observed g at 90% relative humidity (RH), g(90%), ranged from 1.42 to 1.89 with an average of 1.790.11. The g values are significantly lower than that of seawater (2.1) and slightly lower than those previously reported for marine aerosols (>1.8), probably due to the atmospheric processing associated with chlorine depletion; mean Cl-/Na+ molar ratio (1.100.23) was smaller than seawater (1.18), and organometal interaction (e.g., formation of water-insoluble calcium oxalate, g(90%)<1). Inorganic salts accounted for 87-98% of WSM. Na+ and Cl- are two major species, contributing 63% of total inorganic ion mass. The calculated aerosol water content (V-w/V-dry) at 85% RH during hydration experiment ranged from 1 to 3.66 (mean of 2.750.81). V-w/V-dry is negatively correlated with organic mass fraction, indicating that organics may suppress the hygroscopicity of the marine aerosol particles. The declined g(90%) and Cl-/Na+ molar ratio and increased abundance of water-soluble organics in spring demonstrated that the atmospheric mixing of anthropogenic pollutants (e.g., NO3, SOx) and water-soluble organics can decrease the growth factor of marine aerosols. The two case studies of spring aerosols demonstrated that Asian dusts were internally mixed with hygroscopic species in different ways, depending on their transport pathway

Organic and inorganic aerosol compositions in Ulaanbaatar, Mongolia, during the cold winter of 2007 to 2008 : Dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls

To investigate the distributions and sources of water-soluble organic acids in the Mongolian atmosphere, aerosol samples (PM2.5, n = 34) were collected at an urban site (47.92°N, 106.90°E, ∼1300 m above sea level) in Ulaanbaatar, the capital of Mongolia, during the cold winter. The samples were analyzed for water-soluble dicarboxylic acids (C2-C12) and related compounds (ketocarboxylic acids and α-dicarbonyls), as well as organic carbon (OC), elemental carbon, water-soluble OC, and inorganic ions. Distributions of dicarboxylic acids and related compounds were characterized by a predominance of terephthalic acid (tPh; 130 ± 51 ng m^[-3], 19% of total detected organic acids) followed by oxalic (107 ± 28 ng m^[-3], 15%), succinic (63 ± 20 ng m^[-3], 9%), glyoxylic (55 ± 18 ng m^[-3], 8%), and phthalic (54 ± 27 ng m^[-3], 8%) acids. Predominance of terephthalic acid, which has not been reported previously in atmospheric aerosols, was mainly due to uncontrolled burning of plastic bottles and bags in home stoves for heating and waste incineration during the cold winter. This study demonstrated that most of the air pollutants were directly emitted from local sources such as heat and power plants, home stoves, and automobiles. Development of an inversion layer (< 700 m above ground level) over the basin of Ulaanbaatar accelerated the accumulation of pollutants, causing severe haze episodes during the winter season

Evidence of formation of submicrometer water-soluble organic aerosols at a deciduous forest site in northern Japan in summer

Semicontinuous measurements of submicrometer water-soluble organic aerosols and particle size distributions were conducted at a deciduous forest site in northern Japan in August 2010. Increases in particle number concentration were frequently observed in daytime, accompanied by an increase in the concentrations of water-soluble organic carbon (WSOC). We found that daily averaged WSOC concentrations positively correlated with gross primary production of CO2 by the forest ecosystem (r2 = 0.63) and ambient temperature during daytime. These relations suggest that the formation of WSOC is closely linked to photosynthetic activity by the forest ecosystem, which depends on both temperature and solar radiation. Off-line chemical analysis of samples of particles with aerodynamic diameter smaller than 1 μm collected during a 2 day event of elevated WSOC levels suggests that photochemical aging of both α- and β-pinene and isoprene oxidation products contributes to the particle growth and the WSOC mass. Organic tracers of primary biological aerosol particles (PBAPs) showed distinct diurnal variations with a maximum around noontime, also indicating that higher temperature and light intensity induce emissions of PBAPs. However, their contribution to the submicrometer WSOC mass was likely insignificant. During the day, the concentrations of 3-methyl-1,2,3-butanetricarboxylic acid (3-MBTCA) showed a strong dependence on temperature, and the ratios of WSOC to particle volume concentration increased with an increase in the concentration ratios of 3-MBTCA to pinonic acid (PA). This result supports a previous proposal that the 3-MBTCA/PA ratios in submicrometer particles can be a useful tracer for chemical aging of biogenic secondary organic aerosol from forest vegetation

The effects of accumulated refractory particles and the peak inert mode temperature on semi-continuous organic carbon and elemental carbon measurements during the CAREBeijing 2006 campaign

Two semi-continuous Sunset carbon analyzers, with different peak inert mode temperatures (615 and 740℃), were simultaneously operated to measure fine particulate organic carbon (OC) and elemental carbon (EC) using a thermal optical transmittance method at an urban site in Beijing, China, from 16 August to 3 September 2006 during the CAREBeijing 2006 campaign. Excellent agreements were obtained between the collocated semi-continuous carbon analyzers, with slopes of 1.02 (R2 = 0.91) for OC and 1.06 (R2 = 0.93) for EC, resulting in very similar average EC/total carbon (TC) ratios of ∼0.36. These results imply that the different peak inert mode (100% helium) temperatures did not cause significant biases on the semi-continuous OC and EC measurements. However, it was found that the EC/TC ratio was greatly influenced by the accumulated refractory particles remaining on a quartz filter (PM refractory). Fresh quartz filters, with low PM refractory loadings, which is defined as a laser correction factor ≥0.94, gave ∼8-10% lower EC/TC ratios than aged quartz filters with high PM refractory loadings. The linear regression slope between EC and optically measured EC (OPT-EC) was much higher with fresh quartz filters (slope = 1.03, R2 = 0.96) than aged quartz filters (slope = 0.89, R2 = 0.95), suggesting the underestimation of EC on fresh quartz filters by ∼15% compared to those measured on aged quartz filters. Authentic standard humic-like substances (HULIS) on the clean quartz filter showed the highest extent of pyrolyzed organic carbon (POC) formation (47.4% in total detected carbon mass), followed by those on the Asian dust loaded quartz filter (37%) and the refractory urban pollutant loaded quartz filter (34.1%), indicating that the Asian dust and refractory urban pollutant reduced the POC formation from the HULIS. Thus, this study suggested that the PM refractory loading plays an important role in the semi-continuous OC and EC measurements by altering the degree of POC formation in the inert atmosphere