Nobuyuki Takegawa

In the summer of 2006, measurements of the mixing state of non-volatile particles were carried out at a suburban site of Beijing in the North China Plain by using a VTDMA. In this study, we perform an in-depth analysis of VTDMA results, focusing on the following topics: (1) comparison of the mixing state of soot measured by a VTDMA and the aerosol hygroscopicity mixing state determined by a CCN (cloud condensation nuclei) counter; (2) diurnal variation and evolution of soot mixing state at different size ranges; (3) calculation of k_ex→in and the influence of emissions on it; and (4) potential parameterization methods.

Ground‐based measurements of aerosol and trace gases were conducted at a rural site in Beijing in the summer of 2006 as a part of the Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing 2006). The size‐resolved chemical composition of submicron aerosol was measured using an Aerodyne quadrupole aerosol mass spectrometer (AMS). The data obtained from 15 August to 10 September 2006 are presented. Meteorological analysis shows that the measurement period can be characterized as a cycle of low wind speed periods over the course of a few days (stagnant periods) followed by rapid advection of clean air from the north/northwest mostly due to passage of a midlatitude cyclone. Mass concentrations of total measured aerosol with diameters less than 1 μm (total PM₁), which is defined as the sum of elemental carbon and nonrefractory components measured by the AMS, were highly variable, ranging from ∼2 to ∼100 μg m⁻³. Large variability of the PM₁ composition and drastic changes in the sulfate (SO₄²⁻) size distribution were observed to be associated with the cycle of stagnant periods and advection of clean air, indicating that both chemical and physical properties of aerosols were significantly altered on a time scale of a few days. We have found the dominance of organic aerosol at lower total PM₁ mass loadings and that of SO₄²⁻ at higher mass loadings, which may have important implications for the PM control strategy in Beijing. Possible factors affecting the evolution of the mass concentration and size distribution of SO₄²⁻ are discussed.

Ground‐based in situ measurements of sulfur dioxide (SO₂) and submicron sulfate aerosol (SO₄²⁻) together with carbon monoxide (CO) were conducted at an urban site in Tokyo, Japan from spring 2003 to winter 2004. The observed concentrations of SO₂ were affected dominantly by anthropogenic emissions (for example, manufacturing industries) in source areas, while small fraction of the data (2 (power plant and volcano). Although emission sources of CO in Tokyo are different from those of SO₂, the major emission sources of CO and SO₂ are colocated, indicating that CO can be used as a tracer of anthropogenic SO₂ emissions in Tokyo. The ratio of SO₄²⁻ to total sulfur compounds (SO_x = SO₂ + SO₄²⁻) and the remaining fraction of SO_x, which is derived as the ratio of the linear regression slope of the SO_x‐CO correlation, is used as measures for the formation of SO₄²⁻ and removal of SO_x, respectively. Using these parameters, the average formation efficiency of SO₄²⁻ (i.e., amount of SO₄²⁻ produced per SO₂ emitted from emission sources) are estimated to be 0.18 and 0.03 in the summer and winter periods, respectively. A simple box model was developed to estimate the lifetime of SO_x. The lifetime of SO_x for the summer period (26 h) is estimated to be about two times longer than that for the winter period (14 h). The seasonal variations of the remaining fraction of SO_x, estimated formation efficiency of SO₄²⁻, and lifetime of SO_x are likely due to those of the boundary layer height and photochemical activity (i.e., hydroxyl radical). These results provide useful insights into the formation and removal processes of sulfur compounds exported from an urban area.

Ground‐based measurements of aerosols and trace gases were conducted at an urban site in Tokyo (Komaba) and a site 50 km to the north (Kisai) during July–August 2004. An Aerodyne aerosol mass spectrometer (AMS) was deployed at each measurement site to investigate the chemical evolution of submicron organic aerosol (OA) in polluted air. The mass concentrations of OA at the Kisai site were systematically higher than those at the Komaba site and were correlated with ozone under southerly conditions. The rate of increase of OA at the Kisai site is investigated using the photochemical age derived from the ratio of alkyl nitrates to their parent hydrocarbons. The OA concentrations in processed air (age of 8–16 h) were 4–5 times larger than those in fresh emissions (age ∼ 0), suggesting that the OA concentrations can be significantly enhanced within ∼0.5 days under conditions of high photochemical activity.

In situ measurements of trace gases and aerosols were conducted at an urban site in Tokyo (35°39′N, 139°40′E). The data obtained in summer (July–August 2003), fall (September–October 2003), and winter (February 2003 and January–February 2004) are used for the present analysis. Size‐resolved chemical composition of nonrefractory (vaporized at 600°C under high vacuum) submicron aerosol was measured using an Aerodyne aerosol mass spectrometer (AMS). Organics are found to be the dominant component (40–60% of total nonrefractory aerosol mass) in all periods. Organic aerosol (OA) is classified by correlation with carbon monoxide (CO) and fragments of aliphatic and oxygenated organic compounds in the AMS mass spectra. Combustion‐related organic aerosol (combustion OA) is defined as the primary organic aerosol (POA) fraction, as determined by a linear correlation with CO. Excess organic aerosol (excess OA) is defined by subtracting the combustion OA and the background OA from the total OA. The combustion OA and excess OA show good correlation (r² = 0.65–0.85) with hydrocarbon‐like organic aerosol (HOA) and oxygenated organic aerosol (OOA), respectively, which were derived from a custom principal component analysis. In the summer period the estimated excess OA concentrations show distinct diurnal variations and correlate with ozone (O₃) during daytime. On average, the combustion OA does not exhibit a distinct diurnal variation for the summer, fall, and winter periods, while the excess OA shows a clear diurnal pattern (daytime peak at ∼1300 LT). At the daytime peak the excess OA is found to be at nearly the same concentration as the combustion OA for all seasons, suggesting that significant formation of secondary organic aerosol (SOA) occurred in daytime throughout the measurement period.

The Pacific Exploration of Asian Continental Emission Phase A (PEACE‐A) aircraft measurement campaign was conducted over the western Pacific in January 2002. Correlations of carbon monoxide (CO) with carbon dioxide (CO₂) and back trajectories are used to identify plumes strongly affected by Asian continental emissions. ΔCO/ΔCO₂ratios (i.e., linear regression slopes of CO‐CO₂) in the plumes generally fall within the variability range of the CO/CO₂emission ratios estimated from an emission inventory for east Asia, demonstrating the consistency between the aircraft measurements and the emission characterization. Removal rates of reactive nitrogen (NO_xand NO_y) for the study region (altitude 2, the photochemical age of the plumes, and the NO_x/CO₂emission ratio derived from the emission inventory. The plume age is estimated from the rates of hydrocarbon decay and hydroxyl radical (OH) concentration calculated using a constrained photochemical box model. The average lifetime of NO_xis estimated to be 1.2 ± 0.4 days. Possible processes controlling the NO_xlifetime are discussed in conjunction with results from earlier studies. The average lifetime of NO_yis estimated to be 1.7 ± 0.5 days, which is comparable to the NO_ylifetime of 1.7–1.8 days that has been previously reported for outflow from the United States. This similarity suggests the importance of chemical processing near the source regions in determining the NO_yabundance.

In situ aircraft measurements of trace gases and aerosols were made in the boundary layer (BL) and free troposphere (FT) over Indonesia and Australia during the Biomass Burning and Lightning Experiment (BIBLE)-A and B conducted in August–October 1998 and 1999.Concentrations of ozone (O3) and its precursors [CO, reactive nitrogen (NOx), non-methane hydrocarbons (NMHCs)] were measured in these campaigns to identify the sources of NOx and to estimate the effects of biomass burning and lightning on photochemical production of O3. Over Indonesia, in-situ production of NOx by lightning was found to be a major source of reactive nitrogen in the upper troposphere during BIBLE-A. In some circumstances, increases in reactive nitrogen were often associated with enhancements in CO and NMHCs, suggesting that the sources were biomass burning and fossil fuel combustion, followed by upward transport by cumulus convection. Over Australia the levels of O3, CO, reactive nitrogen, and NMHCs were elevated throughout the troposphere compared to those observed in the tropical Pacific. However, the mechanisms responsible for the enhanced concentrations in the BL and FT are distinctly different. The emissions from biomass burning that occurred in northern Australia were restricted to the BL because of strong subsidence in the period. In the FT over Australia, elevated concentrations of O3 and its precursors result from injections of emissions as the air masses travel over Africa, South America, the Indian Ocean, and Indonesia en route to Australia. In all cases, O3 levels in the biomass burning plumes were enhanced due to photochemical production.

The Biomass Burning and Lightning Experiment Phase B (BIBLE‐B) aircraft measurement campaign was conducted over the western Pacific and Australia in August and September 1999. In situ aircraft measurements of carbon monoxide (CO), nitric oxide (NO), total reactive nitrogen (NO_y), ozone (O₃), nonmethane hydrocarbons (NMHCs), and other species were made during BIBLE‐B. Meteorological analysis shows that the trace gases emitted from biomass burning in northern Australia were mostly confined within the planetary boundary layer (below ∼3 km) by strong subsidence in the free troposphere. Removal processes of NO_x (equal to measured NO + calculated NO₂) and NO_y in biomass burning plumes in the boundary layer are examined on the basis of correlation analysis. The photochemical lifetime of NO_x in biomass burning plumes during the daytime is estimated to be 0.1 to 0.3 days using the correlations of NO_x with short‐lived NMHCs and hydroxyl radical (OH) concentration calculated from a constrained photochemical model. Correlation of NO_y with CO shows that ∼60% of the NO_y molecules originating from biomass burning were removed in the boundary layer within 2–3 days. This result is consistent with dry deposition of nitric acid (HNO₃) in the plumes. It is likely that only a small fraction of NO_y emitted from biomass burning was exported from the boundary layer to the free troposphere during the BIBLE‐B period.

In situ aircraft measurements of ozone (O₃) and its precursors were made over northern Australia in August–September 1999 during the Biomass Burning and Lightning Experiment Phase B (BIBLE‐B). A clear positive correlation of O₃ with carbon monoxide (CO) was found in biomass burning plumes in the boundary layer (3/ΔCO ratio (linear regression slope of O₃‐CO correlation) is found to be 0.12 ppbv/ppbv, which is comparable to the ratio of 0.15 ppbv/ppbv observed at 0–4 km over the Amazon and Africa in previous studies. The net flux of O₃ exported from northern Australia during BIBLE‐B is estimated to be 0.3 Gmol O₃/day. In the biomass burning region, large enhancements of O₃ were coincident with the locations of biomass burning hot spots, suggesting that major O₃ production occurred near fires (horizontal scale <50 km).