Hiroshi Furutani

Development and Characterization of an Aircraft Aerosol Time-of-Flight Mass Spectrometer

Vertical and horizontal profiles of atmospheric aerosols are necessary for understanding the impact of air pollution on regional and global climate. To gain further insight into the size-resolved chemistry of individual atmospheric particles, a smaller aerosol time-of-flight mass spectrometer (ATOFMS) with increased data acquisition capabilities was developed for aircraft-based studies. Compared to previous ATOFMS systems, the new instrument has a faster data acquisition rate with improved ion transmission and mass resolution, as well as reduced physical size and power consumption, all required advances for use in aircraft studies. In addition, real-time source apportionment software allows the immediate identification and classification of individual particles to guide sampling decisions while in the field. The aircraft (A)-ATOFMS was field-tested on the ground during the Study of Organic Aerosols in Riverside, CA (SOAR) and aboard an aircraft during the Ice in Clouds Experiment-Layer Clouds (ICE-L). Initial results from ICE-L represent the first reported aircraft-based single-particle dual-polarity mass spectrometry measurements and provide an increased understanding of particle mixing state as a function of altitude. Improved ion transmission allows for the first single-particle detection of species out to approximately m/z 2000, an important mass range for the detection of biological aerosols and oligomeric species. In addition, high time resolution measurements of single-particle mixing state are demonstrated and shown to be important for airborne studies where particle concentrations and chemistry vary rapidly.

Unique ocean‐derived particles serve as a proxy for changes in ocean chemistry

[1]xa0Oceans represent a significant natural source of gases and particles to the atmosphere. Relative to gas phase compounds, less is known regarding the influence of changes in biological activity in the ocean on the chemistry of sea spray aerosols produced in marine environments. To gain insight into the influence of ocean biology and chemistry on atmospheric aerosol chemistry, simultaneous real-time measurements were made of atmospheric aerosol size and chemical mixing-state, gas phase dimethyl sulfide (DMS), as well as seawater DMS and chlorophyll a. In three different marine environments with elevated chlorophyll a and DMS, unique Mg particles were detected containing Mg2+, Ca2+, K+, and organic carbon. These particles were segregated from sea salt particles highlighting that two subpopulations within the sea spray were being ejected from the ocean. Strong temporal correlations were observed between these unique ocean-derived particles and freshly emitted sea salt particles (R2 = 0.86), particularly as wind speed increased to at least 10 m/s, and atmospheric DMS (R2 = 0.76). Time series correlations between ocean measurements and atmospheric aerosol chemistry suggest that chlorophyll a and DMS serve as indicators of changes in the chemistry of the ocean, most likely an increase in organic material, which is directly reflected in the single particle mixing-state. This is the first time such real-time correlations are shown between ocean chemistry and atmospheric aerosol mixing-state. The reasons behind these observed changes in aerosol chemistry are critical for understanding the heterogeneous reactivity, water uptake, and cloud forming potential of sea spray aerosols.

Chemically segregated optical and microphysical properties of ambient aerosols measured in a single‐particle mass spectrometer

[1]xa0This paper describes results from the first direct measurements of the size-resolved optical properties as a function of chemical mixing states for atmospheric particle types sampled in Mexico City and Riverside, California. The coupled size, chemistry, and optical measurements were used to derive refractive indices and effective densities for chemically distinct particle mixing states. On the basis of the measured dependence of scattering intensity as a function of relative humidity and size, the Riverside particles contained detectable amounts of liquid water, whereas the Mexico City particles were relatively dry. Aerosol particles in Mexico City were observed to exhibit a wide range of densities (1.1–3.4 g/cm3), suggesting a dynamic, externally mixed aerosol population. Daily variations were observed as the particles in Mexico City underwent photochemical aging processes leading to a diurnal variation in particle morphology. In contrast, the optical properties of the Riverside aerosol, sampled during the fall season, were strongly impacted by the condensation of water and ammonium nitrate during periods of intense pollution buildup, resulting in microphysical properties that were similar across mixing states for a specific relative humidity.

Seasonal cycles of ozone and oxidized nitrogen species in northeast Asia 1. Impact of regional climatology and photochemistry observed during RISOTTO 1999–2000

[1]xa0Measurements of oxidized nitrogen species, including peroxyacetyl nitrate (PAN), nitrogen oxides (NOx), nitric acid (HNO3), and nonmethane hydrocarbons (NMHCs), were made along with ozone (O3) and carbon monoxide (CO) at Rishiri Island, a remote island in northern Japan, as part of the Rishiri Island Study of Oxidants and Transport for Tropospheric Ozone (RISOTTO). Full seasonal observations of O3, CO, NMHCs, and PAN, together with data sets of NOx, and HNO3 for 6 months reveal short-term and seasonal characteristics of chemistry of the air masses in northeast Asia. Temporal variations of O3, PAN, and HNO3 typically show day-to-day variations in winter and diurnal variations in summer, dominated by long-range transport and local photochemistry, respectively. Seasonal variations of O3 and PAN show a spring maximum and a summer minimum, which are consistent with previous field observations made in Europe and North America. Air mass segregation based on back trajectory calculation suggests that PAN, which is photochemically produced in continental source regions, is most effectively transported to remote sites in spring owing to low temperatures in this season, while HNO3 is not effectively transported due to its high deposition velocity. It is concluded that transport of polluted air masses from continental source regions considerably enhances the April maximum in O3 and PAN observed at remote sites in northeast Asia. Back trajectory analysis also indicates that the seasonal cycles of PAN in the Eurasian continental background air masses are maximum in spring, minimum in summer, and show a secondary maximum in fall in contrast to NOx and HNO3 which have a summer maximum and a winter minimum.

Implications of iodine chemistry for daytime HO2 levels at Rishiri Island

[1]xa0The observed midday maximum in the mixing ratio of HO2 at Rishiri Island in June 2000 was ∼10 pptv, but photochemical box model simulations overpredicted HO2 at this location by an average of 70%. This overestimation was significant only when the mixing ratio of NO was lower than 300 pptv, and was coincident with overprediction of the NO/NO2 ratio. We detected several organoiodines, presumably emitted from seaweeds, and propose the presence of the IO radical. IO could reduce HO2 mixing ratios via the formation of HOI that may subsequently be scavenged by aerosols or lost by photolysis and may also convert NO to NO2 directly. Model calculations with known iodine chemistry could reproduce the observed HO2 with 12–25 pptv of IO. Although iodine chemistry is unlikely to explain the entire discrepancy in HO2, several pptv of IO could significantly reduce HO2 mixing ratios and NO/NO2 ratios.

Development and characterization of a fast measurement system for gas‐phase nitric acid with a chemical ionization mass spectrometer in the marine boundary layer

[1]xa0A chemical ionization mass spectrometer (CIMS) and an automated air sampling/background signal measurement system designed for fast, reliable, and continuous ground-based measurement of gas-phase nitric acid (HNO3) were developed and characterized in a remote marine boundary layer site, Rishiri Island Observatory in Japan, under various meteorological conditions. HNO3 transmission efficiency of air sampling line, interference of NO and NO2 by corona discharge ion source, time response, detection sensitivity, and detection limit of the system were determined under the ambient condition. Detection limit of the system, defined as 3 times the standard deviation of background signal, varied depending on the atmospheric HNO3 concentration, 3–5 parts per trillion by volume (pptv) for the clean condition (HNO3 < 100 pptv) and 15–20 pptv for the polluted condition (HNO3 1–2 ppbv) with 2-s integration time. The determining factor of HNO3 transmission efficiency (HNO3 loss) and critical points for reliable and fast measurement of gas-phase HNO3 in the marine boundary layer were identified on the basis of field and laboratory tests of the CIMS system.

Direct night-time ejection of particle-phase reduced biogenic sulfur compounds from the ocean to the atmosphere.

The influence of oceanic biological activity on sea spray aerosol composition, clouds, and climate remains poorly understood. The emission of organic material and gaseous dimethyl sulfide (DMS) from the ocean represents well-documented biogenic processes that influence particle chemistry in marine environments. However, the direct emission of particle-phase biogenic sulfur from the ocean remains largely unexplored. Here we present measurements of ocean-derived particles containing reduced sulfur, detected as elemental sulfur ions (e.g., (32)S(+), (64)S2(+)), in seven different marine environments using real-time, single particle mass spectrometry; these particles have not been detected outside of the marine environment. These reduced sulfur compounds were associated with primary marine particle types and wind speeds typically between 5 and 10 m/s suggesting that these particles themselves are a primary emission. In studies with measurements of seawater properties, chlorophyll-a and atmospheric DMS concentrations were typically elevated in these same locations suggesting a biogenic source for these sulfur-containing particles. Interestingly, these sulfur-containing particles only appeared at night, likely due to rapid photochemical destruction during the daytime, and comprised up to ∼67% of the aerosol number fraction, particularly in the supermicrometer size range. These sulfur-containing particles were detected along the California coast, across the Pacific Ocean, and in the southern Indian Ocean suggesting that these particles represent a globally significant biogenic contribution to the marine aerosol burden.

Seasonal cycles of ozone and oxidized nitrogen species in northeast Asia 2. A model analysis of the roles of chemistry and transport: OZONE AND SPECIATED NOyIN A GLOBAL CTM

Received 13 November 2001; revised 18 May 2002; accepted 20 May 2002; published 11 December 2002. [1] The dominant factors controlling the seasonal variations of ozone (O3) and three major oxidized nitrogen species, peroxyacetyl nitrate (PAN), nitrogen oxides (NOx), and nitric acid (HNO3), in northeast Asia are investigated by using a three-dimensional global chemical transport model to analyze surface observations made at Rishiri Island, a remote island in northern Japan. The model was evaluated by comparing with observed seasonal variations, and with the relationships between O3, CO, and PAN. We show that the model reproduces the chemical environment at Rishiri Island reasonably well, and that the seasonal cycles of O3, CO, NOy species, and VOCs are well predicted. The impact of local emissions on some of these constituents is significant, but is not the dominant factor affecting the seasonal cycles. The seasonal roles of chemistry and transport in controlling O3 and PAN are revealed by examining production/destruction and import/ export/deposition fluxes in the boundary layer over the Rishiri region. For O3, transport plays a key role throughout the year, and the regional photochemical contribution is at most 10% in summer. For PAN, in contrast, transport dominates in winter, while in-situ chemistry contributes as much as 75% in summer. It is suggested that the relative contribution of transport and in-situ chemistry is significantly different for O3 and PAN, but that the wintertime dominance of transport due to the long chemical lifetimes of these species is sufficient to drive the seasonal cycles of springtime maximum and summertime minimum characteristic of remote sites. INDEX TERMS: 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere— constituent transport and chemistry; 9320 Information Related to Geographic Region: Asia; KEYWORDS: tropospheric ozone, oxidized nitrogen, seasonal cycle, transport, photochemistry Citation: Tanimoto, H., O. Wild, S. Kato, H. Furutani, Y. Makide, Y. Komazaki, S. Hashimoto, S. Tanaka, and H. Akimoto, Seasonal cycles of ozone and oxidized nitrogen species in northeast Asia, 2, A model analysis of the roles of chemistry and transport, J. Geophys. Res., 107(D23), 4706, doi:10.1029/2001JD001497, 2002.