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[1] The Dutch-Finnish Ozone Monitoring Instrument (OMI) launched on the NASA Aura satellite in July 2004 offers unprecedented spatial resolution, coupled with contiguous daily global coverage, for space-based UV measurements of sulfur dioxide (SO 2 ). We present a first validation of the OMI SO 2 data with in situ aircraft measurements in NE China in April 2005. The study demonstrates that OMI can distinguish between background SO 2 conditions and heavy pollution on a daily basis. The noise (expressed as the standard deviation, s) is $1.5 DU (Dobson units; 1 DU = 2.69 Á 10 16 molecules/cm 2 ) for instantaneous field of view boundary layer (PBL) SO 2 data. Temporal and spatial averaging can reduce the noise to s $ 0.3 DU over a remote region of the South Pacific; the long-term average over this remote location was within 0.1 DU of zero. Under polluted conditions collection 2 OMI data are higher than aircraft measurements by a factor of two. Improved calibrations of the radiance and irradiance data (collection 3) result in better agreement with aircraft measurements on polluted days. The air mass-corrected collection 3 data still show positive bias and sensitivity to UV absorbing aerosols. The difference between the in situ data and the OMI SO 2 measurements within 30 km of the aircraft profiles was about 1 DU, equivalent to $5 ppb from 0 to 3000 m altitude. Quantifying the SO 2 and aerosol profiles and spectral dependence of aerosol absorption between 310 and 330 nm are critical for an accurate estimate of SO 2 from satellite UV measurements.

a b s t r a c tChina's urbanization has been a notable global event. The National New Urbanization Plan (2014)(2015)(2016)(2017)(2018)(2019)(2020) unveiled by the Chinese Central Government revealed a new path for urbanization that accommodated unique Chinese characteristics. The most notable aspect was the transfer from land-centered urbanization to people-oriented urbanization. Given that land urbanization was the key to the previous orbit, this manuscript aims to analyze the evolution and challenge for land-centered urbanization, and way forward for people-oriented urbanization in China. With increasing urban populations and expanding industrial activities, China has experienced vigorous land urbanization and an uneven population distribution pattern since 1978. Land-centered urbanization has created some economic and social benefits, but has also posed many adverse impacts. The issues of the loss of arable land, the phenomenon of "ghost cities," and the urban heat island effect have become critical challenges. Eight suggestions from two perspectives are recommended in this manuscript for achieving new-type urbanization in China. We should give priority to this issue of the citizenization of peasant migrants. Government, scientists, and the public can all combine to influence the development trajectories of China's new-type urbanization.

[1] Papers published in this special section report findings from the East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST-AIRE). They are concerned with (1) the temporal and spatial distributions of aerosol loading and precursor gases, (2) aerosol single scattering albedo (SSA), (3) aerosol direct radiative effects, (4) validation of satellite products, (5) transport mechanisms, and (6) the effects of air pollution on ecosystems. Aerosol loading is heaviest in mideastern China with a mean aerosol optical depth (AOD) of 0.5 and increasing to 0.7 around major cities that reduced daily mean surface solar radiation by $30-40 W m À2 , but barely changed solar reflection at the top of the atmosphere. Aerosol loading, particle size and composition vary considerably with location and season. The MODIS AOD data from Collection 5 (C5) agree much better with ground data than earlier releases, but considerable discrepancies still exist because of treatments of aerosol SSA and surface albedo. Four methods are proposed/adopted to derive the SSA by means of remote sensing and in situ observation, which varies drastically with time and space. The nationwide means of AOD, Å ngström exponent, and SSA (0.5 mm) in China are 0.69 ± 0.17, 1.06 ± 0.26, and 0.89 ± 0.04, respectively. Measurements of trace gases reveal substantial uncertainties in emission inventories. An analysis of aircraft measurements revealed that dry convection is an important mechanism uplifting pollutants over northern China. Model simulations of nitrogen deposition and impact of ozone pollution on net primary productivity indicate an increasing threat of air pollution on the ecosystem.