Air Quality Research Branch

Toronto, Canada

Air Quality Research Branch

Toronto, Canada
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Tsigaridis K.,Columbia University | Tsigaridis K.,NASA | Daskalakis N.,University of Crete | Daskalakis N.,Foundation for Research and Technology Hellas | And 91 more authors.
Atmospheric Chemistry and Physics | Year: 2014

This paper evaluates the current status of global modeling of the organic aerosol (OA) in the troposphere and analyzes the differences between models as well as between models and observations. Thirty-one global chemistry transport models (CTMs) and general circulation models (GCMs) have participated in this intercomparison, in the framework of AeroCom phase II. The simulation of OA varies greatly between models in terms of the magnitude of primary emissions, secondary OA (SOA) formation, the number of OA species used (2 to 62), the complexity of OA parameterizations (gas-particle partitioning, chemical aging, multiphase chemistry, aerosol microphysics), and the OA physical, chemical and optical properties. The diversity of the global OA simulation results has increased since earlier AeroCom experiments, mainly due to the increasing complexity of the SOA parameterization in models, and the implementation of new, highly uncertain, OA sources. Diversity of over one order of magnitude exists in the modeled vertical distribution of OA concentrations that deserves a dedicated future study. Furthermore, although the OA / OC ratio depends on OA sources and atmospheric processing, and is important for model evaluation against OA and OC observations, it is resolved only by a few global models. The median global primary OA (POA) source strength is 56 Tg a-1 (range 34-144 Tg a-1) and the median SOA source strength (natural and anthropogenic) is 19 Tg a-1 (range 13-121 Tg a-1). Among the models that take into account the semi-volatile SOA nature, the median source is calculated to be 51 Tg a-1 (range 16-121 Tg a-1), much larger than the median value of the models that calculate SOA in a more simplistic way (19 Tg a-1; range 13-20 Tg a-1, with one model at 37 Tg a-1). The median atmospheric burden of OA is 1.4 Tg (24 models in the range of 0.6-2.0 Tg and 4 between 2.0 and 3.8 Tg), with a median OA lifetime of 5.4 days (range 3.8-9.6 days). In models that reported both OA and sulfate burdens, the median value of the OA/sulfate burden ratio is calculated to be 0.77; 13 models calculate a ratio lower than 1, and 9 models higher than 1. For 26 models that reported OA deposition fluxes, the median wet removal is 70 Tg a-1 (range 28-209 Tg a-1), which is on average 85% of the total OA deposition. Fine aerosol organic carbon (OC) and OA observations from continuous monitoring networks and individual field campaigns have been used for model evaluation. At urban locations, the model-observation comparison indicates missing knowledge on anthropogenic OA sources, both strength and seasonality. The combined model-measurements analysis suggests the existence of increased OA levels during summer due to biogenic SOA formation over large areas of the USA that can be of the same order of magnitude as the POA, even at urban locations, and contribute to the measured urban seasonal pattern. Global models are able to simulate the high secondary character of OA observed in the atmosphere as a result of SOA formation and POA aging, although the amount of OA present in the atmosphere remains largely underestimated, with a mean normalized bias (MNB) equal to -0.62 (-0.51) based on the comparison against OC (OA) urban data of all models at the surface, -0.15 (+0.51) when compared with remote measurements, and -0.30 for marine locations with OC data. The mean temporal correlations across all stations are low when compared with OC (OA) measurements: 0.47 (0.52) for urban stations, 0.39 (0.37) for remote stations, and 0.25 for marine stations with OC data. The combination of high (negative) MNB and higher correlation at urban stations when compared with the low MNB and lower correlation at remote sites suggests that knowledge about the processes that govern aerosol processing, transport and removal, on top of their sources, is important at the remote stations. There is no clear change in model skill with increasing model complexity with regard to OC or OA mass concentration. However, the complexity is needed in models in order to distinguish between anthropogenic and natural OA as needed for climate mitigation, and to calculate the impact of OA on climate accurately. © Author(s) 2014.

Deng Z.-Q.,Lanzhou Arid Meteorological Institute of China Meteorological Administration | Deng Z.-Q.,Key Open Laboratory of Arid Climate Change and Disaster Reduction of China Meteorological Administration | Han Y.-X.,Lanzhou Arid Meteorological Institute of China Meteorological Administration | Han Y.-X.,Key Open Laboratory of Arid Climate Change and Disaster Reduction of China Meteorological Administration | And 4 more authors.
Zhongguo Huanjing Kexue/China Environmental Science | Year: 2011

Relationship between dust aerosol and solar radiation in gebi desert in North China was analyzed based on observational and calculative data, such as TOMS aerosol index (AI), total astronomical radiation, total solar radiation and dust visibility. in China mainland. It turns out that there were perfect correlation and same trend between the total solar radiation and AI, suggesting that the thermal convection triggered by solar radiation was the most important factor for dust aerosol. It also shows that the input of dust aerosol in atmosphere would affect solar radiation significantly and persistently. Besides these, the ratio of absorption and scattering of solar radiation by dust aerosol between fine days and sandstorm was above 60%.

Zhang H.,National Climate Center | Wang Z.,Chinese Academy of Meteorological Sciences | Wang Z.,National Climate Center | Liu Q.,National Climate Center | And 7 more authors.
Climate Dynamics | Year: 2012

An interactive system coupling the Beijing Climate Center atmospheric general circulation model (BCC_AGCM2. 0. 1) and the Canadian Aerosol Module (CAM) with updated aerosol emission sources was developed to investigate the global distributions of optical properties and direct radiative forcing (DRF) of typical aerosols and their impacts on East Asian climate. The simulated total aerosol optical depth (AOD), single scattering albedo, and asymmetry parameter were generally consistent with the ground-based measurements. Under all-sky conditions, the simulated global annual mean DRF at the top of the atmosphere was -2. 03 W m-2 for all aerosols including sulfate, organic carbon (OC), black carbon (BC), dust, and sea salt; the global annual mean DRF was -0. 23 W m-2 for sulfate, BC, and OC aerosols. The sulfate, BC, and OC aerosols led to decreases of 0. 58° and 0. 14 mm day-1 in the JJA means of surface temperature and precipitation rate in East Asia. The differences of land-sea surface temperature and surface pressure were reduced in East Asian monsoon region due to these aerosols, thus leading to the weakening of East Asian summer monsoon. Atmospheric dynamic and thermodynamic were affected due to the three types of aerosol, and the southward motion between 15°N and 30°N in lower troposphere was increased, which slowed down the northward transport of moist air carried by the East Asian summer monsoon, and moreover decreased the summer monsoon precipitation in south and east China. © 2011 Springer-Verlag.

Binyamin J.,University of Winnipeg | Davies J.,McMaster University | McArthur B.,Air Quality Research Branch
International Journal of Climatology | Year: 2010

Cloud optical properties play a highly significant role in the amount of UV-B irradiance reaching the ground. Broadband values of UV-B cloud optical properties are calculated for nine Canadian stations from 26 years of data. Cloud single scattering albedo ωc and asymmetry factor gc are computed from Mie theory for two values of equivalent droplet radius; 7 μm for arctic stations and 10 μm for midlatitude and subarctic stations. Overcast cloud optical depths τc are estimated iteratively for a model cloud layer located between 2 and 3 km above the surface from hourly integrated spectral Brewer spectrophotometer measurements for snow-free cases using either the discrete ordinate radiative transfer (DISORT) or the delta-Eddington algorithms. Median τc values calculated by both algorithms compare to within 3%. Median values are smaller for arctic stations (9-18) and between 26 and 38 for the rest. Both mean and median values are negatively correlated with latitude. Aerosol effect on τc varies between 9 and 18% on average. © 2009 Royal Meteorological Society.

Wang Z.L.,Chinese Academy of Meteorological Sciences | Wang Z.L.,National Climate Center | Zhang H.,National Climate Center | Shen X.S.,Chinese Academy of Meteorological Sciences | And 3 more authors.
Advances in Atmospheric Sciences | Year: 2010

Aerosol indirect effects (AIEs) on global climate were quantitatively investigated by introducing aerosol-cloud interaction parameterizations for water stratus clouds into an AGCM (BCC_AGCM2. 0.1), which was developed by the National Climate Center of the China Meteorological Administration. The study yielded a global annual mean of -1.14 W m-2 for the first indirect radiative forcing (IRF), with an obvious seasonal change. In summer, large forcing mainly occurred in mid to high latitudes of the Northern Hemisphere, whereas in winter, large values were found at 60°S. The second indirect effect led to global annual mean changes in net shortwave flux of -1.03 W m-2 at the top of the atmosphere (TOA), which was relatively significant in mid-latitude regions of both hemispheres. The total AIE reduced the global annual means of net shortwave flux at the TOA and of surface temperature by 1.93 W m-2 and 0. 12 K, respectively. Change in surface temperature induced by the total AIE was clearly larger in the Northern Hemisphere (-0. 23 K) than in the Southern Hemisphere, where changes were negligible. The interhemispheric asymmetry in surface cooling resulted in significant differences in changes of the interhemispheric annual mean precipitation rate, which could lead to a tendency for the ITCZ to broaden. The total AIE decreased the global annual mean precipitation rate by 0.055 mm d-1. © 2010 Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg.

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