Environmental Pollution 195 (2014) 233e235
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Air pollution in Asia It is a pleasure for us to be the Guest Editors for this special issue of “Air Pollution in Asia” focusing on Greenhouse Gas (GHG) emissions, climate impacts, and modeling. GHG's and short-lived climate pollutants (SLCP) from the Asian region have been increasing continuously associated with rapid population growth and increased industrial activities (Atkinson et al., 2012). Coal is still the major source of energy in many Asian countries, and consequently, there is an increase in coal smoke, with suspended particulate matter, sulfur dioxide (SO2) and Nitrogen dioxide (NO2) as the predominant pollutants (Leung et al., 2012; Kurokawa et al., 2013). Biomass burning, primarily from land use practices is also a major contributor of aerosols and GHG's in the region (Andreae and Merlet, 2001; Vadrevu et al., 2013; Shi et al., 2013). In addition, the rapidly growing number of motor vehicles in the region has accelerated the emissions of other ambient air pollutants such as nitrogen dioxide (NO2) and ozone (O3) (Leung et al., 2012). As a result, air pollution levels in many Asian cities are well above World Health Organization guideline values, resulting in asthma and allergy-related health issues (Atkinson et al., 2012). It is well-recognized that air pollution is no longer just a local problem, but a trans-boundary issue requiring regional cooperation. For example, the recent biomass burning episode of June 2013 in Riau Province, Indonesia impacted all the downwind neighboring countries in Southeast Asia including Malaysia, Singapore, Brunei and southern Thailand (Vadrevu et al., 2014). The pollution not only caused visibility issues in different countries but also health and climate concerns. From the Southeast Asia, aerosols can be elevated by mid-latitude wave cyclones and sometimes can travel long distances to possibly inﬂuence climate and weather patterns. Recently, speciﬁc to climate impacts, Wang et al. (2014) has shown Asian pollution invigorates winter cyclones over the northwest Paciﬁc, increasing precipitation by 7% and net cloud radiative forcing by 1.0 W m 2 at the top of the atmosphere and by 1.7 W m 2 at the Earth's surface. Another important aspect relating to GHG's and SLCP's in the Asian region is the need for accurate inventories and reporting (Akimoto, 2003; Ohara et al., 2007). Various measurement systems are in place in the region including, ground based, satellite, airborne, etc., but few of these are truly operational. No single system can provide all the necessary data and to address air quality and climate impacts of GHG's, several studies infer the need to integrate both top-down and bottom-up approaches including modeling (Martin et al., 2003; Kim et al., 2014). To address the above issues, an international workshop entitled “Inventory, Modeling and Climate Impacts of Greenhouse Gas emissions (GHG's) and Aerosols in the Asian Region” was organized during 26the28th June, Tsukuba, Japan, 2013. Participants included 90 attendees from 15 different countries. The workshop was http://dx.doi.org/10.1016/j.envpol.2014.09.006 0269-7491/© 2014 Elsevier Ltd. All rights reserved.
sponsored by University of Maryland College Park, USA, National Institute for Environmental Studies (NIES), Tsukuba, Japan, Global Observation of Forest and Land Cover Dynamics (GOFC-GOLD) program, USA and International SysTem for Analysis Research and Training (START), Washington DC. The workshop was organized into ﬁve different sessions: 1). Regional campaigns/studies in Asia; 2). Anthropogenic emission inventories in Asia; 3). Earth Observation Programs in Land Cover/Land Use/Air Pollution/GHG emissions and Coordination Activities; 4). Biomass burning emissions; 5). Aerosols, climate change and air quality; 6). the Southeast Asia Regional Research and Information Network (SEARRIN). The latter part of the session focused on a round-table discussion highlighting the need of regional cooperation for effective collaboration in terms of capacity building, training and data sharing for addressing the pollution problem in Asia. This special issue is an outcome of the above workshop and it synthesizes the latest research on GHG emissions, aerosols and modeling, while reviewing other important regional campaigns and developments relating to air quality in the Asian region. We are most fortunate to have attracted 11 high quality papers involving researchers from different countries, i.e., Japan, Vietnam, Indonesia, Philippines, Taiwan, India, USA, etc. The papers cluster into three different topic areas: a). GHG inventories from different sectors; b). Impacts of GHG's and aerosols on climate and c). Use of models for emission inventories, quantifying impacts and emission reduction. A short summary of the papers is provided below. The ﬁrst six papers in the special issue focus on emissions from different sectors in Korea, biomass burning emissions in Indonesia and Vietnam, pollutant variations in rural and urban areas of India, and factors affecting CO2 variations in Thailand/Philippines. GHG emission inventories of North Korea are very rare and contain large uncertainties (Kim et al., 2014, 2014). In the ﬁrst paper entitled “Veriﬁcation of NOx emission inventories over North Korea”, Kim et al., use satellite-derived top-down approaches with the bottom-up GHG emissions for quantifying the NOx emissions from 1996 to 2009. Authors found REAS 1.1 GHG data closely matching with the top-down satellite estimates. NOx emissions from the industrial sector seemed to be the highest during 1980's and decrease in the 1990's in North Korea. Authors report NOx emissions from the agriculture and domestic sectors as the second highest after the transportation sector for post-1990's (Kim et al., 2014). These trends seem different compared to other countries, especially neighboring South Korea. Another unique characteristic authors report with respect to NOx emissions in North Korea is the seasonality; the monthly NOx emissions in North Korea seem to be high during the warm season and low during the cold season. This is in contrast to other developing countries where NOx emissions are higher during the cold season and lower during the
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warm season. These results are unique and need further investigation. An important question of signiﬁcance with respect to satellite retrievals of air pollutants is how well do they capture temporal and spatial variations and how well do they relate to episodic events such as ﬁres? Answering such questions can help in developing real-time pollution monitoring systems from satellites. Vadrevu et al. (2014) addresses this topic in the study entitled “Analysis of Southeast Asian pollution episode during June 2013 using satellite remote sensing datasets”. The authors use both the yearly and daily data on aerosol optical depth (AOD), ﬁne mode fraction (FMF), aerosol absorption optical depth (AAOD) and UV aerosol index (UVAI) for characterizing variations. The authors report signiﬁcant enhancement in aerosols and CO during the pollution episode and stronger correlations of ﬁre counts with AAOD and UVAI compared to AOD and FMF. Using the Hysplit trajectory model, authors show the transport of air masses from Indonesia towards Malaysia, Singapore and southern Thailand. In their study, authors highlight the potential and limitations of some of the atmospheric remote sensing products useful for biomass burning studies. Peat land ﬁres are most prevalent in Indonesia. Emission inventories on peat land ﬁres are urgently needed to understand their impacts on the environment, associated health aspects as well as to account for GHG uncertainties. The paper entitled “Peat-ﬁre related air pollution in Central Kalimantan, Indonesia”, by Hayasaka et al. (2014) describes the haze events from peat ﬁres in Palangkaraya, Indonesia. Authors use ground-based pollutant data on PM10, SO2, CO, O3 and NO2 to assess pollutant variations in peat land ﬁres from late-August to late-October. They report a signiﬁcant increase of the above pollutants resulting from peat land ﬁres. Authors report a signiﬁcant increase in PM10 during early-August, reaching a maximum value during mid-October, followed by a decline during late October mainly due to change from dry to wet season. Hayasaka et al. (2014) also stress the importance of peat land conservation measures to reduce air pollution in the study region. In the paper entitled “Vegetation ﬁres and air pollution in Vietnam”, Ha et al. (2014) integrate ground-based measurements and satellite data to describe vegetation ﬁres. The authors infer that in addition to the urban pollution, biomass burning is a major contributor of GHG's including CO, SO2, total suspended particles, particulate matter, etc. Authors map the ﬁre data spatially and report the north-west and central highlands of Vietnam as major hotspots of biomass burning, mainly due to shifting agriculture in forested land and agricultural residue burning respectively. They also analyze the relationship between satellite atmospheric variables and ground-based air pollutant data and show a good correlation between MOPITT CO, UV aerosol index, etc. They also report a strong dependence of particulate matter on Aerosol Optical Thickness (AOT) increase, based on aerodynamic diameters. The authors stress the need to develop a real-time ﬁre-air pollution monitoring system in Vietnam to help address air quality issues in Vietnam. Rapid population growth together with industrial development is major concern impacting air quality and environment in India. In the study entitled “Spatial and temporal patterns of air pollutants in rural and urban areas of India” authors Sharma and Kulshrestha use ground-based pollution monitoring data to infer spatial variations. They infer that districts of central and northern India have relatively higher suspended particulate matter (SPM) concentrations compared to southern India. They also relate SPM concentrations to population densities. In the same study, authors also show relatively higher correlation of satellite-derived aerosol optical depth data with SPM, SO2 and NO2 in urban areas compared to the rural areas.
In the study entitled “Factors inﬂuencing surface CO2 variations in LPRU, Thailand and IESM, Philippines’, Macatangay et al. (2014) use ground-based measurements of CO2 and meteorological data in a multiple-regression framework to assess CO2 variations. They show that air temperature and sea level pressure were the dominant meteorological factors impacting CO2 variations. Also, the authors use the Stochastic Time-Inverted Lagrangian Transport (STILT) model, driven by the meteorological ﬁelds of the Global Data Assimilation System model, to map trans-boundary transport of CO2 from the source regions to assess variations. An important paper in this special issue is by Lin et al. (2014), which reviews the interactions between biomass-burning aerosols and clouds over Southeast Asia. An extensive list of remote sensing instruments useful for cloudeaerosol interactions is provided. Of the different instruments, the most useful one is the CALIPSO mission which helps in characterizing the aerosol vertical distribution which is particularly useful to relate to ground-based aerosol measurements, including source characterization such as from biomass burning and dust. Data from ground-based instruments and sensor networks available from sun-photometer, sky-radiometer and Lidar are also listed in the study. In the paper, impacts of smoke aerosols on drought as well as net primary productivity are also reviewed. Authors also highlight several regionally relevant campaigns in Asia, such as INDOEX, ACE-Asia, TRACE-P, 7-SEAS, etc. These campaigns identify biomass burning as an important source of trace gas emissions and aerosols in the region with both regional and global climate impacts. Lin et al. (this issue), conclude that biomass burning aerosol impacts on clouds and precipitation is less clear in Southeast Asia and to better understand these relationships, there is a need to integrate ground-based, satellite and modeling studies. The last four papers in the special issue by Yumimoto et al., Dai et al., Goto et al., and Hanaoka et al., focus on modeling. In contrast to the bottom-up emission inventory approach, the inverse modeling techniques infer source emissions from observed mixing ratios, thus allowing retrieval of information on source strengths and optimization of the agreement between model and observational data (Henze et al., 2009; Yumimoto and Uno, 2006). In the paper entitled “Long-term inverse modeling of Chinese CO emission from satellite observations”, Yumimoto et al. (2014) use Green's function method of inversion in conjunction with MOPITT CO data for the emission inventory. Authors also compare their inverse modeling results with the bottom-up estimates of CO in China. GEOS-Chem model was used to calculate the sourceereceptor relationship of CO. Their results from inverse modeling show considerable seasonal variations closely matching the satellite data and bottom-up emission inventories; inparticular, a decreasing trend in CO emissions after 2007. They attribute this decrease to the global recession in that year and improved combustion efﬁciency for the other years. In recent times, aerosol transport models have emerged as an important tool for ﬁlling the observational gaps, providing an efﬁcient way of understanding both the spatial and temporal evolutions of aerosol properties including climate impacts (Schutgens et al., 2010; Dai et al., 2014). Assimilation aims to combine both the information from the model simulations and the observations to obtain an optimal solution with reduced uncertainties (Dai et al., 2014). In the paper entitled “Improvement of aerosol optical properties modeling over Eastern Asia with MODIS AOD assimilation in a global non-hydrostatic icosahedral aerosol transport model”, Dai et al. (2014) develop a new aerosol assimilation system based on the local ensemble transform Kalman Filter and a nonhydrostatic icosahedral aerosol transport model. The authors perform sensitivity experiments using aerosol optical depth retrieved from MODIS and the resulting AOD and Ångstrom Exponent validated with independent observations from the Aerosol
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Robotic Network (AERONET) (Holben et al., 1998). The authors found that the ensemble perturbation method has the largest effect on assimilation results compared to the local patch sizes in which experiments are performed. Also, the results highlight the importance of assimilation in reproducing events of short duration that are often missed by the standard model because of the lack of accurate emissions data. Black carbon (BC) emitted from fossil fuel combustion and biomass burning can absorb solar radiation resulting in positive radiative forcing. Several modeling studies in Asia underestimate the impacts of BC radiative forcing due to the lack of groundbased measurements for improved parameterization of BC in aerosol-transport models. Goto et al. (2014) in the study entitled “Modeling of black carbon in Asia using a global-to-regional seamless aerosol-transport model” compare two different models i.e., NICAM and MIROC over Asia in terms of BC spatial gradients and conclude that NICAM-simulated BC mass concentrations are lower in lower elevations (