## 1 Introduction  
According to international inventories, most of atmospheric particulate carbons in large cities such as Seoul, Korea, come from combustion processes such as coal and fuel combustion, diesel exhausts, open burning at construction sites and residential areas [1, 2]. These airborne particulates contain various components, some of which adversely affect human health. A field test on the urban roads revealed a proportional relationship between carbons and traffic amount [3]. In particular, morning rush hour traffic contributed 8-9% of the total elemental carbon (EC) in the local air.  
There were several reports that PM\({}_{10}\) levels ranged from 6.73 to 20.8 \(\upmu\)g/m\({}^{3}\) in schools far from the road, and from 9.20 to 32.8 \(\upmu\)g/m\({}^{3}\) in schools near the road [4, 5]. Thus, the school children located in a crowded inner city face harsh environmental conditions. One reference emphasizes building conditions for maintaining safe indoor air quality especially in city schools [6]. The carbon content in macrophages of the respiratory tract is inversely associated with lung function particularly in children. Thus, the capacity and growth of school children respiratory systems near main roads are worse than those in remote areas [7]. Carbonaceous components occupy 10 to 40% of the aerosols suspended in urban atmosphere [8]. Mass fractions of organic carbon (OC) and EC in PM\({}_{2.5}\) of downtown Seoul were 0.13 \(\pm\) 0.06 and 0.05 \(\pm\) 0.03 respectively [9]. In particular, EC which is mainly emitted from cars in large cities exists in the form of aggregates (0.1-1 \(\upmu\)m) composed of tiny spherules ranging in size between 0.001 and 0.005 \(\upmu\)m particles which belong to PM\({}_{2.5}\)[10]. Since fine particulate carbons can contain various harmful substances, a particular attention should be paid to carbonaceous species.  
It was found that the ratio of indoor to outdoor (I/O ratio) carbons varied from lower than 1 to 1.9 depending on indoor activities and source contributions [11]. Residents are at high risk of exposure from contaminants present in indoor spaces. In accordance, higher I/O ratio would be undesirable given the likely negative health effects for indoor occupants. Depending on the region and building conditions, approximately 40% of the mass of indoor PM\({}_{2.5}\) consists of carbonaceous matters, and the OC mass fraction is two to five times higher than that of EC [8; 12]. Among the government controlled indoor environments in public places, air quality of school classrooms where young students stay for a long time is particularly important.  
There is a study carried out in China, emphasizing the importance of school air quality by tracking the OC sources around the school [13]. Most of school indoor EC are originated from air infiltration through unintentional leaks of building envelope and window gap or wall cracks as well as window openings. While some researches have been conducted on indoor air in private homes, little has been done on carbon levels in school classrooms [14].  
Thus, to investigate carbonaceous aerosols in school environment, particulate matters such as PM\({}_{2.5}\) and PM\({}_{10}\) were sampled and quantitatively analyzed from classrooms and playgrounds. This study also focused on the daily class hours of students. The obtained data will be fruitfully used to inform the establishment of a national school environment management policy. Elementary schools are rarely open to the general public, even including academic researchers, but this time, a comprehensive investigation on air quality was allowed with the aid of the Ministry of Environment.