1. Time series of satellite-based fine particulate matter (PM 2.5 ) concentrations over China: 2004-2012 Guannan Geng, Qiang Zhang, Aaron van Donkelaar, Randall V. Martin, and Kebin He 2013-12-11, San Francisco

2. Sources and negative effects of fine particles (PM 2.5 ) Climate Brown Cloud Acid rain Haze Health Increased morbidity and mortality from both acute and chronic exposure to ambient fine particulate matter (PM 2.5 ) fine particulate matters in the (ambient) air with 2.5 micrometers or less in size

3. Regional haze is a major concern in China Beijing haze Primary pollutants in 74 cities (2013.1-10) PM 2.5 concentration (2013.1-10) Heavy PM 2.5 pollution occurs in China, especially in the North China Plain

4. How has PM 2.5 evolved over the past decade over China? Long-term variation of PM 2.5 concentrations is important for epidemiological studies. China has developed control strategies for the precursors of PM 2.5, e.g. SO 2 and NO x. But ground measurements are limited in China –Only several research groups have monitored the ground level PM 2.5 concentration before the year 2013. –National network of PM 2.5 monitoring is built up since 2013.

5. Satellite Remote sensing approach can be used to enhance our ability to estimate PM 2.5 concentration Many works have used aerosol optical depth (AOD) to retrieve PM 2.5 concentration In this study, ground-level PM 2.5 concentrations for the period 2004-2012 over China are estimated using CTM to provide the conversion factor between PM 2.5 and AOD. Multiple linear regression Chemical transport model

6. Satellite-derived surface PM 2.5 van Donkelaar et al, EHP, 2010 van Donkelaar et al, JGR, 2013 GEOS-Chem (GC) PM 2.5 AOD MISR CALIPSO AOD Vertical Profile emissions MEIC

7. Emission trends of the precursors in China The MEIC inventory, 2004-2012

8. Evaluation of model simulations SNA simulation in the year of 2006 Modeled AOD trend compared with MISR Slope = 0.28, R = 0.32 Slope = 0.26, R = 0.33 Slope = 0.19, R = 0.17 Slope = 0.85, R = 0.39 Slope = 0.44, R = 0.81 Slope = 0.52, R = 0.78 Slope = 0.68, R = 0.71 Slope = 0.86, R = 0.88 Slope = 0.58, R = 0.66 Slope = 0.79, R = 0.82 Slope = 0.64, R = 0.49 Slope = 0.93, R = 0.74

9. Satellite-based PM 2.5 retrieved from MISR AOD

10. Trends of the conversion factor and MISR AOD Modeled PM 2.5 Modeled PM 2.5 /AOD MISR AOD Modeled AOD

11. The population weighted national annual mean PM 2.5 trends over China during 2004-2012 10 4

12. PM 2.5 trends of some cities in China

13. The effect of the correlation slope between modeled and satellite AOD on PM 2.5 trend

14. Conclusions National scale surface PM 2.5 concentration derived from MISR increased from 2004 to 2006 and started to decrease around 2006- 2007, and had a second small peak in 2011. The trend between 2004 and 2012 was +0.5 ug·m -3 ·yr -1. In the Northern China, there are mostly increasing trends, even above 4 ug·m -3 ·yr -1 in some regions. While in the Southern China, PM 2.5 decreased in 2012 compared to 2004. PM 2.5 concentrations in some megacities have started to decrease slightly.