Atmospheric Chemistry Group
Research Areas
The upper figure shows the air measuring platform on the roof of an academic building at Rutgers Newark campus, which was built in 2006 with atmospheric devices installed. A number of Rutgers graduate students have collected air samples on this platform for their thesis research. Undergraduate students also participated in air sampling at the platform.
The lower figure shows the results derived from aerosol samples collected on this platform: (1) Particulate matter in the air at Newark was dominated by fine particles of ~0.5 microns in diameter in both summer and winter; (2) Fine particles of ~0.5 microns in the air were higher in summer than in winter, due to high temperature and strong solar radiation in summer that promoted photochemical reactions for the formation of secondary particulate pollutants in the air (Zhao & Gao, 2008).
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1. Urban Air Quality Studies in the US Northeast Coast, with a particular focus on Newark in NJ since 2005
Urban air pollution has drawn increasing attention due to its impacts on air quality, human health, and regional and global climate change. Air pollutants, both primary and secondary, may exist in aerosol-, gas-, and precipitation- phases, functioning differently. Therefore, air quality is affected by the interactions of different air components and environmental factors. The research on urban air pollution that the Gao group has continually carried out since 2005 is primarily based at Rutgers Newark campus, and Newark is the largest metropolitan center in New Jersey adjacent to New York City. The subjects of research in the Gao group include:
- Particulate matter of PM2.5 in the NY-NJ Harbor Bight (Gao
et al., 2002).
- Ionic species in urban particles at Newark (Zhao & Gao,
2008).
- Urban heat island at Newark (Thuman, 2009).
- Precipitation composition and acid rain at Newark (Song &
Gao, 2009).
- Traffic emissions of toxics and fugitive dust (Song & Gao, 2012; Xia & Gao, 2010).
- Nitrogen oxides and ground-level ozone around Newark
(Roberts-Semple et al., 2012).
- Impact of urban air pollution on human health around
Newark (Roberts-Semple and Gao, 2013).
- Aerosol iron solubility at Newark (Xu & Gao, 2017).
- Atmospheric organic carbon and elemental carbon at Newark
(Gonzalez, 2020).
- Microplastics in the air around Newark (Yao et al., 2021).
- Impact of the COVID-19 pandemic on air auality in metropolitan New Jersey (Yao et al., 2022).
Atmospheric field work was conducted at Rutgers Marine Field Station at Tuckerton in Southern NJ. This photo shows the Gao group installing air samplers on a narrow pathway between the station complex and the met tower. Results from measurements of precipitation and aerosols at this site showed that atmospheric deposition contributed a significant amount of nitrogen to Barnegat Bay (Gao, 2002).
2. Atmospheric N Deposition to NJ Coastal Waters
The coastal atmosphere adjacent to or downwind of large urban and industrial centers can be strongly impacted by pollution emissions, and high concentrations of pollutants in the coastal air could result in enhanced air-to-sea deposition fluxes. One of the consequences is accelerated coastal primary production (or eutrophication) driven by excessive discharges of nutrients, such as nitrogen (N), from both point and non-point sources, such as atmospheric deposition. With earlier work on the Asian coast, quantifying atmospheric N and its deposition was carried out on the New Jersey coast, including Barnegat Bay (Gao, 2002) and Mullica River-Great Bay estuary (Ayars and Gao, 2007) in Southern New Jersey. The combined atmosphere-water column measurements in northern and southern New Jersey suggest that atmospheric deposition appears to be an important pathway of new N inputs to New Jersey coastal waters and a potentially significant N enrichment source for biotic production (Gao et al., 2007).
Upper photo: Air sampling platform installed on the eighth-floor front deck of the Chinese icebreaker, Xue Long, to support atmospheric measurements. The cruise was made through the Southern Ocean from West Australia to the Chinese Zhongshan Station in East Antarctica and in coastal waters from Zhongshan Station to Casey Station, Antarctica (Gao et al., 2013).
Lower photo: Atmospheric sampling tower at Palmer Station in West Antarctic Peninsula to support atmospheric measurements. This platform was installed at a site between the station complex and the glaciers, called Palmer Backyard (Gao et al., 2020).
3. Southern Ocean/Antarctic Atmospheric Chemistry
The Southern Ocean plays an important role in the global carbon cycle and climate change. However, much of it belongs to the category of HNLC waters, where primary production is limited by the micronutrients such as iron (Fe), besides light, temperature, etc. Some Antarctic coastal seas are highly productive and receive Fe from Antarctic continental shelf sediments and glacier/ice melt; however, some of the nearby pelagic waters in the Southern Ocean are Fe-limited and thus could receive Fe from other sources, including the atmospheric deposition. To address this issue, the shipboard experiments of aerosols were conducted on the Chinese icebreaker, XueLong, in the Southern Ocean and East Antarctica for aerosol Fe solubility and size distributions (Gao et al., 2013) and water-soluble organic and inorganic species (Xu et al., 2013 & 2021). Ground-based atmospheric measurements were also carried out at Palmer Station in the West Antarctic Peninsula for aerosol Fe properties (Gao et al., 2020), aerosol elemental composition (Fan et al., 2021), and secondary organic aerosols (Deng et al., 2021). With the continued NSF support, the Gao group will be heading to the Amundsen Sea in West Antarctica to explore the roles of atmospheric input on the biogeochemical cycle in the Antarctic continental shelf waters.
This figure shows the US GEOTRACES Western Arctic GN01 section from Dutch Harbor, Alaska to the North Pole. Air sampling was made aboard the US Coast Guard Icebreaker Healey with the use of a MOUDI sampler (M), and sampling periods (M1-M8) during this cruise were marked with different colors. Particle-size distributions of iron-containing aerosol particles and relevant solubility of aerosol iron were measured for the first time in this region. Results suggest that dust sources around the Arctic Ocean may have been altered by climate warming (Gao et al., 2019).
4. Atmospheric Composition over the Arctic
The Arctic temperature has increased over the last 100 years. One factor that may contribute to the warming could be the role of the short-lived absorbing aerosol particles, such as black carbon. On the other hand, the atmospheric composition over the Arctic Ocean could be highly impacted by natural and anthropogenic emissions in the surrounding continents, and the input of nutrients from the atmospheric long-range transport could affect the marine ecosystem in this oceanic basin. To explore the unknowns on this aspect, field measurements of black carbon, selected trace elements, and ionic species were conducted in the Svalbard Archipelago in the Arctic Ocean, based at the Chinese Yellow River Station at Ny-Ålesund (Zhan and Gao, 2014; Zhan et al., 2017). Shipboard atmospheric measurements were also made as part of the US GEOTRACES western GN01 cruise on the US Coast Guard icebreaker, the Healy, from Dutch Harbor, Alaska all the way to the North Pole and back (Gao et al., 2019; Mukherjee et al., 2020 & 2021). The results from these efforts have contributed to the new knowledge of better understanding the interactions of the atmosphere-ocean-anthropogenic perturbation in this complicated polar environment.
This figure shows the images of selected individual aerosol particles collected on a transect from Hawaii in the North Pacific to the Asian coast aboard the NOAA R/V Ronald H. Brown during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia); a total of 11,482 aerosol particles from samples collected on this cruise were examined through individual-particle analysis (Gao et al., 2007). The evidence of the reactions of Asian dust particles with anthropogenic SO2 was found in aerosols collected in Northern and coastal China (Gao and Anderson, 2001).
5. Dust Particles Characterization
As an aerosol, dust affects the Earth’s radiation budget through direct and indirect effects. The degrees of both effects are dominated by chemical and physical properties of dust. Dust particles also provide reaction sites for many heterogeneous reactions involving SO2, NOx, HOx, O3, etc. and serve as conveyors carrying anthropogenic substances from the continents to the remote environments through the long-range transport. Those processes may alter the chemical and physical properties of dust, such as iron solubility and then its bioavailability to the surface ocean biota. Particle composition was examined by SEM (Gao and Anderson, 2001; Gao et al., 2007) and the effects of organic ligands, light, and acidity on the solubility of Fe-rich particles were tested by wet lab procedures (Xu & Gao, 2008). Currently, the Gao group is taking a closer look at Fe oxidation state through synchrotron-based near-edge X-ray absorption spectroscopy.
6. Quantifying Atmospheric Deposition of Nutrient Elements to the Ocean through Integrating Observational Data and Model Simulations
Many atmospheric processes, such as heterogeneous reactions with acidic species and organic ligand complexation, may convert insoluble nutrient elements in aerosols, such as Fe in dust, to soluble forms that become bioavailable for phytoplankton uptake in the surface ocean. Results from observations including Zhao and Gao (2008) and Xue et al. (2013) and laboratory experiments including Xu and Gao (2008) were applied to the numerical models to explore the processes and mechanisms that affect the fluxes of soluble iron to the ocean on the global scale (Lu & Gao, 2010). Seasonal variation of aeolian Fe fluxes to the global ocean was characterized through the combination of surface-based and satellite data (Gao et al., 2001). Precipitation scavenging was identified as a potential driver for natural iron fertilization in the ocean (Gao et al., 2003).
Upper figure: NASA MODIS data for a dust episode off the African coast on 29 Feb 2000. The left part of the image is a composite image of MODIS aerosol products (Gao et al., 2001).
Lower figure: Results of model simulations of soluble iron deposition to the global ocean affected by oxalate, an organic ligand that originates from both natural and anthropogenic sources (Luo & Gao, 2010).
This figure shows the air mass trajectories as related to (a) the highest dust concentration observed at Midway Island (M) in the North Pacific when the air masses originated in or passed over the desert regions in China, and (b) the lowest dust concentration when there was little or no evidence for direct transport from Asia (Gao et al., 1992a).
7. Atmospheric Transport of Asian Dust over the North Pacific Ocean and Natural and Anthropogenic Impact on Atmospheric Composition over East Asia
Among the most critical environmental events are the Asian dust storms that often occur in the spring. The dust storms disrupt human activities and link the biogeochemical cycles through the land, atmosphere, and ocean. For example, the flux of mineral aerosol affects the distributions of dissolved iron and aluminum in the open sea. The mid-latitudes of the North Pacific are strongly influenced by Asian dust, and this material is a significant source for deep-sea sediments. The primary sources of Asian dust include sandy deserts distributed in the west and northwestern China and tremendous accumulations of loess and extensive areas of the Gobi in northern and northeastern China. Research results showed that the sources of Asian dust and its transport patterns impacting the marine atmospheric composition between Western-north Pacific and remote North Pacific were uniquely different (Gao et al., 1992a). Atmospheric dust deposition contributed a significant fraction of mineral matter to the total input in the Yellow Sea (Gao et al., 1992b), and non-sea-salt sulfate and nitrate aerosols over the China Sea were derived mainly from anthropogenic sources (Gao et al., 1996). Anthropogenic emissions could have perturbed the natural cycles of atmospheric dust over East Asia (Gao et al., 1997).