Abstract
This study investigated the seasonal variation of nitrate concentration and its radiative forcing over East Asia by using an online-coupled regional climate model. Comparison with a series of in-situ observations from Acid Deposition Monitoring Network in East Asia (EANET) and China demonstrated a good skill of the model in reproducing the magnitude and seasonality of nitrate concentration across East Asia. It was found that nitrate concentration in Beijing and Tianjin exhibited the maximum in summer and the minimum in winter possibly due to stronger chemical oxidation and regional transport effect of larger emissions from the north China Plain in summer, whereas in most areas of East Asia, nitrate concentration was higher in winter and lower in summer, consistent with the seasonality of NOx emission. Surface nitrate concentration was higher over the lower reaches of the Yellow River, followed by the middle to lower reaches of the Yangtze River and portions of south China, and lower in Korean Peninsula and Japan. The annual mean surface nitrate concentration was predicted to be 2.9 μg·m−3 for East Asia and 8.5 μg·m−3 for east China. All-sky direct radiative forcing (DRF) due to nitrate at the top of the atmosphere (TOA) exhibited the largest forcing up to −7 W·m−2 over the lower reaches of the Yellow River, and lower forcing of ~−2 W·m−2 in the Korean Peninsula and Japan. Clear-sky DRF by nitrate reached the maximum in spring and the minimum in summer over both East Asia and east China, whereas DRF under all-sky condition showed its maximum in autumn, associated with seasonalities of nitrate column burden, relative humidity, and cloud effect. Annual mean all-sky DRFs at TOA were estimated to be −1.7 W·m−2 and −3.7 W·m−2 over East Asia and east China, respectively, significantly larger than global annual mean, suggesting the important role of nitrate aerosol in environment and climate change over East Asia.
Highlights
Aerosol pollution in East Asia has become a serious problem in the past decades mainly due to continuous economic growth and ineffective emission control in this region
This study aims to investigate seasonal variations of nitrate concentration and its direct radiative forcing over East Asia by using an online-couple regional climate model (RIEMS-Chem: Regional Integrated Environmental Model System with atmospheric chemistry)
Namely sulfate, nitrate, ammonium, black carbon (BC), organic carbon (OC), other anthropogenic particulate matters (AnthPM), dust, and sea salt are considered in this model
Summary
Aerosol pollution in East Asia has become a serious problem in the past decades mainly due to continuous economic growth and ineffective emission control in this region. It was clear that NOx emission had the most rapid increase among pollutants relating with aerosols This implies that nitrate aerosol plays a more and more important role in China in recent years. Nitrate plays important roles in environment and climate change, concerns paid to nitrate are much less than other aerosol types such as sulfate, black carbon, and mineral dust, especially over East Asia/China where intensive emissions of nitrate precursors (NOx ) exist. Previous studies on nitrate aerosol over East Asia/China were limited nitrate accounts for a large fraction of anthropogenic aerosols Most of those studies only investigated the spatial distribution of nitrate concentration in a short time period and model comparison with observation was usually insufficient (e.g., [18,19,20,21]). This study provides valuable information for further understanding the aerosol’s roles in radiation and climate change in this region and for global estimation of nitrate aerosol
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