Global Modeling of Secondary Organic Aerosol With Organic Nucleation

Organic nucleation has been identified as an important way to form secondary organic aerosol (SOA) and change the number concentration of aerosol and thus its climate effect. A global atmospheric chemistry model is developed to include a comprehensive organic nucleation scheme that includes heteromolecular nucleation of sulfuric acid and organics, neutral pure organic nucleation, and ion‐induced pure organic nucleation. Our model simulation shows reasonable agreement with the seasonal as well as spatial pattern of organic carbon concentration in America, while it fails to predict the seasonal pattern of organic carbon in Europe due to the lack of sharp increases in primary organic aerosol emissions in the winter. Including organic nucleation decreases the bias of the annual average particle number concentration at 54% of the available observation sites and increases the temporal correlation coefficients at 58% of the sites. Ion‐induced pure organic nucleation contributes the most to the total organic nucleation rate, which peaks around 400 hPa in the tropics. Heteromolecular nucleation of sulfuric acid and organics dominates the total organic nucleation rate in the summer and mostly occurs in the lower troposphere. The number concentration of particles formed from organic nucleation (newSOA) in the nucleation and Aitken modes is highest in the tropics, while accumulation mode newSOA is highest in the Northern Hemisphere due to growth as a result of the condensation of sulfate. Three sensitivity experiments suggest that more studies are needed to investigate the formation mechanism of newSOA, so that a more accurate simulation of the spatial and size distribution of newSOA can be developed.Key PointsA new version of the CESM/IMPACT atmospheric model is developed to include three organic nucleation schemesIncluding organic nucleation improves the model’s ability to simulate aerosol number concentrationIon‐induced pure organic nucleation is the largest contributor to the global new organic particle formationPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151313/1/jgrd55629_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151313/2/jgrd55629.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151313/3/jgrd55629-sup-0001-Figure_SI-S01.pd

Processes of intraseasonal snow cover variations over the eastern China during boreal winter

This study reveals that the dominant time scale of intraseasonal snow cover variation over the eastern China is within 30 days by using the latest satellite snow cover data from the moderate resolution imaging spectroradiometer (MODIS)/Terra product. The leading empirical orthogonal function (EOF) mode of 10–30‐day snow cover variation during boreal winter from 2004 to 2018 over the eastern China has two centers: northwest part of the eastern China and north of the Yangtze River. Composite analysis based on 25 snow events identified from normalized leading principal time series (PC1) indicates that the southeastward intrusion of surface anticyclonic anomalies and accompanying low temperature anomalies provide the temperature condition for snow events. Negative Arctic Oscillation induces mid‐latitude wave train and leads to the development of surface anticyclonic anomalies and upper‐level cyclonic anomalies over East Asia. The cyclonic anomalies induce ascending motion and anomalous convergence of water vapor fluxes over the eastern China, which supplies moisture for snowfall.(a) Time evolution of composite NAO index (pink curve), AO index (blue curve), regional mean surface air temperature anomalies (°C) (black curve) and snow cover anomalies (%) (red curve) in the region of 20–40°N, 105–120°E. (b) Time evolution of composite anomalies of regional mean snow cover tendency (%/day) (black curve), vertical velocity (Pa/s) (blue curve), and divergence of water vapor flux integral from 1,000 to 100‐hPa (*10−6 kg/(m2*s)) (pink curve) in the region of 20–40°N, 105–120°E. Dots on the curves indicate anomalies significant at the 95% confidence level.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149343/1/asl2901_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149343/2/asl2901.pd

Impacts of different urban canopy schemes in WRF/Chem on regional climate and air quality in Yangtze River Delta, China

AbstractYangtze River Delta (YRD) region has experienced a remarkable urbanization during the past 30years, and regional climate change and air pollution are becoming more and more evident due to urbanization. Impacts of urban canopy on regional climate and air quality in dry- and wet-season are investigated in this paper, utilizing the Weather Research and Forecasting/Chemistry (WRF/Chem) model. Four regimes of urban canopy schemes with updated USGS land-use data in actual state of 2004 base on MODIS observations are examined: (1) SLAB scheme that does not consider urban canopy parameters (the control experiment in this paper); (2) a single-layer urban model with a fixed diurnal profile for anthropogenic heat (UCM); (3) multilayer urban canopy model (BEP-Building effect parameterization); (4) multilayer urban models with a building energy model including anthropogenic heat due to air conditioning (BEP+BEM). Results show that, compared with observations, the best 2-m temperature estimates with minimum bias are obtained with SLAB and BEP+BEM schemes, while the best 10-m wind speed predictions are obtained with BEP and BEP+BEM scheme. For PM10 and ozone predictions, BEP+BEM scheme predicted PM10 well during January, while the best estimate of PM10 is obtained with UCM scheme during July, BEP+BEM and SLAB schemes best estimated ozone concentrations for both the two months. Spatial differences of meteorological factors between canopy schemes and control scheme show that compared with SLAB scheme, BEP and BEP+BEM schemes cause an increase of temperature with differences of 0.5°C and 0.3°C, respectively, UCM scheme simulates lower temperature with decrease of 0.7°C during January. In July, all the canopy experiments calculates lower air temperature with reduction of 0.5°C–1.6°C. All the canopy experiments compute lower 10-m wind speed for both January and July. Decreases were 0.7m/s (0.8m/s) with UCM, 1.7m/s (2.6m/s) with BEP, and 1.8m/s (2.3m/s) with BEP+BEM schemes in January (July), respectively. For chemical field distributions, results show that, compared with SLAB scheme, UCM scheme calculates higher PM10 concentration in both January and July, with the differences of 22.3% (or 24.4μg/m3) in January, and 31.4% (or 17.4μg/m3) in July, respectively. As large as 32.7% (or 18.3 μg/m3) of PM10 increase is found over Hangzhou city during July. While 18.6% (or 22.1 μg/m3) and 16.7% (or 24.6 μg/m3) of PM10 decreases are fund in BEP and BEP+BEM schemes during January. Compared with control experiment during January, 6.5% (or 2.6ppb) to 10.4% (4.2ppb) increases of ozone are computed over mage-cities by canopy experiments. All the three canopy schemes predict lower ozone concentrations and as large as 30.2% (or 11.2ppb) decrease is obtained with UCM scheme, and 16.5% (6.2ppb) decrease with BEP scheme during July. The SLAB scheme is suitable for real-time weather forecast while multiple urban canopy scheme is necessary when quantify the urbanization impacts on regional climate

Variation of Traits on Seeds and Germination Derived from the Hybridization between the Sections Tacamahaca and Aigeiros of the Genus Populus

Poplar is an important research organism, and species in sections Tacamahaca and Aigeiros, have advantages in terms of stress resistance, ease of propagation, and fast growth. Poplar species are widely distributed and well-adapted in the world, presenting a large potential for genetic improvement. Hybridization between different species allows us to generate offspring with a unique combinations of traits. This approach has a huge potential for breeding new poplar varieties that could aid in controlling desertification in the arid and semi-arid zones of the “Three-North” in China. In this study, we carried out a cross test scheme with nine female and thirteen male poplar trees. A total of 105,401 seeds were collected from 117 crosses. Flowering phenology and seed maturation differences of the hybrid progeny were monitored in greenhouses. For male trees, Populus deltoides had the longest flowering time. For female trees, Populus pseudo-simonii showed the longest seed maturity time. The number of carpals and ovules were not the same in different females. Meanwhile, three carpals were found in P. pseudo-simonii. A highly significant positive correlation was found between the seed size and the Thousand Kernel Weight, as well as the seedling cotyledon length. During seed germination, non-radicle and non-hypocotyl seedlings were observed. We also observed a number of cotyledon variants, including single and fused cotyledons, two cotyledons with one cotyledon cracking into two parts, three cotyledons, as well as four cotyledons. These results lay a favorable foundation for combining the research between the sections Tacamahaca and Aigeiros in future work