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  • Author or Editor: Gregory R. Carmichael x
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Gregory R. Carmichael
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Yang Zhang
and
Gregory R. Carmichael

Abstract

A detailed gas-phase chemistry mechanism is combined with dust surface uptake processes to explore possible impacts of mineral dust on tropospheric chemistry. The formations of sulfate and nitrate on dust are studied along with the dust effects on the photochemical oxidant cycle for the long-range-transported particles with a diameter of 0.1–40 μm.

The results show that mineral dust may influence tropospheric sulfate, nitrate, and O3 formation by affecting trace gas concentrations and the tropospheric oxidation capacity through surface processes. The postulated heterogeneous mechanism provides a plausible interpretation for the observed high nitrate and sulfate on dust and the anticorrelation between O3 and dust in East Asia. The presence of dust results in decreases in the concentrations of SO2 (10%–53%), NO p y (16%–100%, defined as NO3 + N2O5 + HNO3), H x O y (11%–59%, defined as OH + HO2 + H2O2), and O3 (11%–40%) under model conditions representative of spring dust storms in East Asia. The decrease in solar actinic flux and the surface uptake of O3 and its precursors contribute to the total O3 decrease for the conditions studied. Nitrate and sulfate, 0.9–2.1 and 0.3–10 μg m−3, respectively, are formed on dust particles, mostly in the size range of 1.5–10 μm. The magnitude of the dust effect strongly depends on the preexisting dust surfaces, the initial conditions, and the selection of model parameters associated with surface uptake processes. The impact of dust reactions on O3 reduction is highly sensitive to the uptake coefficient and to the possible renoxification from the surface reaction of HNO3 on dust.

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Yiwen Xu
and
Gregory R. Carmichael

Abstract

The dry deposition model was created to estimate SO2 and sulfate dry deposition velocities over nine land use types in Asia. The study domain is 20°S–50°N, 39°–154°E. Monthly averaged 1° × 1° dry deposition velocities are estimated for four seasons. Model results show that the dry deposition velocity of SO2 demonstrates strong seasonal and diurnal variability in summer, fall, and spring. In summer, the daytime velocity (in centimeters per second) for SO2 forests is 0.4, over cultivation is 0.2, grassland is 0.5, and ocean is 0.8. Nighttime values of SO2 are two or three times less than daytime values. In winter, the deposition velocity of SO2 does not show much diurnal variability—the value is 0.1–0.2 except over ocean, when it is 0.5. Contrary to SO2, the dry deposition velocity of sulfate only slightly varies with seasons and time of the day. Generally, its value is less than 0.1.

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Toshihiro Kitada
,
Gregory R. Carmichael
, and
Leonard K. Peters

Abstract

The characteristics of the transport of chemically reactive species under land- and sea-breeze (LSB) circulations are investigated using a detailed transport/chemistry model, which includes 84 gas-phase and 10 heterogeneous chemical reactions. Model applications are presented which use flow fields derived from a modified version of the Asai and Mitsumoto model and eddy diffusivity profiles predicted by the boundary-layer model of Yamada and Mellor as inputs. The effects of nonprecipitating clouds associated with the LSB circulation on the calculated concentration fields are also studied.

Mass transports by updrafts and counterflows associated with the LSB circulation and diurnally varying eddy diffusion processes show transitions between double and single maxima within a 24-hour cycle. The vertical profiles of some secondary pollutants such as O3 generally agree with field observations. Clouds are also shown to affect the predicted distributions of both the soluble and less soluble species by reducing the below-cloud photon flux, by removing soluble species from the air at cloud level, and/or by in-cloud production processes. Deposition processes reduce the species concentrations near the surface, and these effects propagate upward through mass transport processes. However, the qualitative characteristic vertical concentration profiles are similar to the cases where deposition is not included. Finally, the results demonstrate the effectiveness of the divergence correction method used in the numerical calculations in eliminating the fictitious production and consumption reactions introduced by nonzero divergence wind fields.

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Yang Zhang
,
Young Sunwoo
,
Veerabhadra Kotamarthi
, and
Gregory R. Carmichael

Abstract

The influence of dust on the tropospheric photochemical oxidant cycle is studied through the use of a detailed coupled aerosol and gas-phase chemistry model. Dust is a significant component of the troposphere throughout Asia and provides a surface for a variety of heterogeneous reactions. Dust is found to be an important surface for particulate nitrate formation. For dust loading and ambient concentrations representative of conditions in East Asia, particulate nitrate levels of 1.5–11.5 µg m−3 are predicted, consistent with measured levels in this region. Dust is also found to reduce NOx levels by up to 50%, HO2 concentrations by 20%–80%, and ozone production rates by up to 25%. The magnitude of the influence of dust is sensitive to the mass concentration of the aerosol, relative humility, and the value of the accommodation coefficient.

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Mahesh J. Phadnis
,
Gregory R. Carmichael
,
Yoichi Ichikawa
, and
Hiroshi Hayami

Abstract

A comparison between transport models is done to study the sulfur deposition in East Asia. A single-layer Lagrangian model with simple chemistry is compared to a multilayered 3D Eulerian model. The comparison is done for two-month-long episodes of winter (February) and summer (August) 1989. The model-predicted sulfur deposition is about 0.1 g S (m2 month)−1 for regions with the largest emissions. A comparison between the model-predicted and the observed values at a network of monitoring stations in Japan shows similar temporal trends. The sulfur deposition due to volcanic emissions in Japan has been shown to be about 20% of the total deposition in that country.

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Changhyoun Park
,
Christoph Gerbig
,
Sally Newman
,
Ravan Ahmadov
,
Sha Feng
,
Kevin R. Gurney
,
Gregory R Carmichael
,
Soon-Young Park
,
Hwa-Woon Lee
,
Mike Goulden
,
Jochen Stutz
,
Jeff Peischl
, and
Tom Ryerson

Abstract

To study regional-scale carbon dioxide (CO2) transport, temporal variability, and budget over the Southern California Air Basin (SoCAB) during the California Research at the Nexus of Air Quality and Climate Change (CalNex) 2010 campaign period, a model that couples the Weather Research and Forecasting (WRF) Model with the Vegetation Photosynthesis and Respiration Model (VPRM) has been used. Our numerical simulations use anthropogenic CO2 emissions of the Hestia Project 2010 fossil-fuel CO2 emissions data products along with optimized VPRM parameters at “FLUXNET” sites, for biospheric CO2 fluxes over SoCAB. The simulated meteorological conditions have been validated with ground and aircraft observations, as well as with background CO2 concentrations from the coastal Palos Verdes site. The model captures the temporal pattern of CO2 concentrations at the ground site at the California Institute of Technology in Pasadena, but it overestimates the magnitude in early daytime. Analysis of CO2 by wind directions reveals the overestimate is due to advection from the south and southwest, where downtown Los Angeles is located. The model also captures the vertical profile of CO2 concentrations along with the flight tracks. The optimized VPRM parameters have significantly improved simulated net ecosystem exchange at each vegetation-class site and thus the regional CO2 budget. The total biospheric contribution ranges approximately from −24% to −20% (daytime) of the total anthropogenic CO2 emissions during the study period.

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