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Continuous in situ measurements of aerosol optical properties have been conducted since March 2010 at a semi-arid rural site in Northeastern China - Tongyu (44.56°N, 122.92°N, elevation 151 m), a reference site of Coordinate Water and Energy cycle Observation Project (CEOP). Aerosol optical properties derived from the measurements during two spring seasons in 2010 and 2011 are analyzed and presented here. Mean values (and standard deviation) of light absorption coefficient (αab) and scattering coefficient (αsc) at 520 nm were 7.61 Mm–1 (6.17 Mm–1) and 89.22 Mm–1 (88.37 Mm–1), respectively, in spring of 2010, and were 7.01 Mm–1 (5.60 Mm–1) and 85.34 Mm–1 (116.11 Mm–1), respectively, in spring 2011. These values are lower than the majority of measurements made in other areas of China. The mean single scattering albedo (ω) was 0.90, greater than values found in some developed areas in China, indicating more scattering or less absorbing aerosols at Tongyu site. Mean values (and standard deviation) of the Angstrom exponent of absorption (αab) were 1.61 (0.27) and 1.64 (0.28) for spring of 2010 and 2011, respectively, and of the scattering (αsc) were 1.48 (0.50) and 1.10 (0.50), respectively. The values of αab were higher than those of pure BC, implying the presence of other light absorbing materials having larger αab values. The moderate values of αsc indicated that considerable amount of coarse particles presented at Tongyu site. Distinct diurnal variations of aerosol optical properties were observed. ω, αab and αsc had nearly opposite diurnal variations compared to those of αab and αsc. Dust aerosols from the northwest and anthropogenic aerosols from the south were major sources contributing to the episodic aerosol events and thus, unusual aerosol optical properties, in spring at Tongyu site. High levels of PM2.5, if mainly caused by dust particles, do not necessarily introduce high values of αab and αsc.

The Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by the Regional Atmospheric Modeling System (RAMS) was applied to East Asia to investigate the transport and photochemical transformation of tropospheric ozone during the Transport and Chemical Evolution over the Pacific (TRACE-P) field campaign. Modeled concentrations of hydroxyl radical, hydroperoxyl radical, nitric oxide, nitrogen dioxide, ethene, ethane, carbon monoxide, and ozone were compared with observations obtained onboard of two aircrafts in order to evaluate the model performance. Comparison indicates that the model reproduced the tempo-spatial distributions of ozone and its related chemical species reasonably well, and most model results were within a factor of 2 of the observations.

The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is applied to East Asia to analyze the production and transport processes of sulfur compounds in the springtime of 2001, when two large field campaigns TRACE-P (TRAnsport and Chemical Evolution over the Pacific) and ACE-Asia (Aerosol Characterization Experiment - Asia) were being conducted over a broad area covering northeastern Asia and the western pacific. Simulated concentrations of sulfur dioxide (SO"2) and sulfate aerosol (SO"4^2^-) were compared with observed data obtained on the ground level at three remote sites in South Korea and China and onboard aircraft C130, and it was found that the modeling system reproduced many of the important features in the observations, including horizontal and vertical gradients, of the Asian pollution outflow over the western Pacific. Analysis of model results shows that the SO"2 and SO"4^2^- concentrations exhibited pronounced variations in time and space, with SO"2 and SO"4^2^- behaving differently due to the interplay of chemical conversion, removal and transport processes.