Analysis of Urban Forest Needs as Anthropogenic (CO2) Gas Absorbent in Semarang City

Green open space in cities in significant needs to maintenance environment quality. On of the critical function is to absorb increasing number of gas CO 2 . Therefore, developing urban forest in cities is very importance. The objective of the study is to determine the area of urban forest as CO 2 gas anthropogenic absorb which is formed from fuel, diesel fuel, liquid petroleum gas. The study consists of (1) Analyzing the number of CO 2 gas emission by calculating the needs of petroleum and gas based on the number of population, (2) Analyzing the power of gas absorption, (3) Measuring the air concentration of CO 2 gas ambient based on daily traffic activities. This study shown that from year 2013 to year 2017, the increasing of urban forest is not so significant. For year 2013 the green open space in Semarang City are 373.67 hectares (7.5 percent from Semarang City area), consists of 239 parks, 11 public cemeteries, production forests, community forests, and urban forests, however the area of urban forest is not increase. The study assess that Antidesmabunius is one of the green species which high absorb capacity planted for Semarang. This trees produce 31,31 ton annually. This study proposed to fostering Antidesmabunius as one principle threes in Semarang urban forest.


Introduction
Semarang is the principal city in central Java. Semarang has a function of of central Java government, centre of service socio-economic, centre of trade and industrial. Which high growth on population, economic, and physical development, Semarang needs sufficient green infrastructure to support urban life [1]. Recently, public green open space in Semarang only 7,5% of the area. While according to the spatial planning regulation, a city requires at least 20% of the area. One of the problem to increase the green open space is land constraints [2]. It is known that the limitation of green open space will be increase air pollution, since CO 2 emission is not converted in urban environment.
Nowadays the concentration of CO 2 in tend to increase highly due to cities activities. Major of contributor is burning fossil fuels, electricity consumption, industries activities. Those activity estimated 65% of total emissions. In addition, about 14% comes from agricultural activities, 18% deforestation, domestic activity and waste decomposition [3]. One effort to maintain and control the concentration of CO 2 is to increase the area of green open space. Green open space is a part of urban forest [4].
The real impact of the rapid development of physical facilities and infrastructure are the reduction of green open space and the increasing consumption of fossil energy. the increasing consumption of fossil energy makes the urban environment become polluted. The increasing of CO 2 will make the urban environment unhealthy and reduce human health, therefore the concentration of CO 2 in the air should be maintenance. One way to reduce in urban areas is to reduce carbon emissions and build urban forests [5]. Urban forests are the most effective carbon sinks that can reduce carbon emissions in the atmosphere. Photosynthesis is an important process in the role of carbon cycle and maintaining in the atmosphere at the same time also play the oxygen cycle. Shifting cultivation, logging and forest fires in absorbing gas decreases. To help overcome the decline in forest function, it is necessary to build urban forest [6].
The balance of population growth with the availability of green open space will maintain health and comfort for the community. Therefore, the greening movement in Semarang City to neutralize the impact of air pollution should be further intensified. In order to achieve the air quality of Semarang City in the present and future period, it is necessary to research concerning to urban forest as an anthropogenic gas absorber in order to maintain the air quality in Semarang City [7,8].
The green of the city not only makes the city beautiful and cool but the aspect of sustainability, harmony and balance of natural resources will make comfort, freshness, freedom of the city from pollution and noise. it makes the citizen of the city healthy and intelligent [8].

Literature Review
Urban forest is an ecosystem. It is not like forest definition in general. Urban forest is a community of plants in the form of trees and its association which grows in urban land or around the city, path shaped, spreading or clustering with the structure that imitate natural forests, forming a habitat which allows life for animals and leads to a healthy, comfortable and aesthetic environment [9]. Urban Forest according to Fakuara [10] is defined as a woody vegetation plant in urban areas that provide enormous environmental advantages in the use of protection, recreation, and environmental aesthetics. In addition, there are two approaches used in building urban forest; The first approach, all areas in a city are basically the area for urban forest. In this approach, the components of a city such as settlements, offices and industries are viewed as a part of a forest in the city [5]. The second approach, urban forest is built in certain locations. In this approach urban forest is part of a city.
Urban forest is considered to have an advantage in absorbing CO 2 compared to parks, since it occupies a wider expanse of the park and consists of several height stratums

Carbon Dioxide gas
Normal air contains a gas consisting of 78% nitrogen; 20% oxygen; 0.93% argon; 0.03% (300 ppm) of carbon dioxide, and the remainder consists of heon, helium, methane and hydrogen. This composition can support human life. Carbon dioxide ( ), methane (CH 4), and nitrogen oxide ( O) are some examples of greenhouse gas (GHG) which cause greenhouse effect (GHE).Greenhouse Effect (GHE).
Greenhouse effect is useful for living things on earth. If there is no greenhouse gas, the average temperature on Earth is only 18 o C. This temperature is too low for most living things, including humans. However, due to the greenhouse effect, the average temperature on earth becomes 33 0 C higher, compare to the normal condition which estimated 15 o C. This temperature is suitable for the life of living beings [11]. Carbon dioxide is the most dominant greenhouse gas that occurs naturally and had significant role in the biological system of the world. Carbon dioxide and water are raw materials for photosynthesis. The carbon flow from atmosphere to vegetation is a two-way flow, which is the binding of to the atmosphere through the process of decomposition and combustion and the absorption of by plants.

Fuel Oil and Gas
Humans need oil fuel obtained from petroleum. Petroleum is a complex mixture composed mostly of hydrocarbons. Hydrocarbons contained in petroleum are mainly , and cyclotane ( ). Crude oil contains about 500 types of hydrocarbons with C -1 to 50 C atoms. In organic chemistry, hydrocarbon compounds, especially paraffinic and aromatic ones, have their own boiling points, of which the hydrocarbon chain rods are proportional to their boiling point. Meanwhile, the length of the hydrocarbon chain is proportional with greater boiling point and density. Therefore, petroleum processing (purification) is carried out by multilevel distillation, in which crude oil is separated into clusters [12]. After being distillated, the boiling point of petroleum fraction can be differentiated into oil and gas fuels as seen in Table 1: Source : [13]

Photosynthesis
Photosynthesis is the process of metabolism in plants with the help of chlorophyll and light, producing carbon dioxide and water into carbohydrates and oxygen molecules. The process of photosynthes is takes place on mesophyll tissue, because the tissues there is chloroplast where there is also chlorophyll. Chloroplast consists of two parts: (1) Tilakoid composed of that allows the conversion of light energy into chemical energy. (2) Lamela the liquid part (less solid) which is where reduction occurs in the dark reaction. Carbon dioxide gas as the main ingredient of photosynthesis enters through stomata. Plant productivity can be appropriately estimated by measuring both oxygen and carbon dioxide used in photosynthesis because the amount of C in is directly proportional to the amount of C bound in sugar during photosynthesis, productivity can be expected by the disappearance of in the environment [14].

Plant As a Gas Absorber
Plants that are in and around the city can be directed to overcome the greenhouse effect. The greenhouse effect is a symptom of warmer air temperatures, especially in the city center. Forest and city parks can absorb gas. City Forest can create a cool and comfortable micro climate Therefore, the greenhouse effect can be overcome well by the vast city forest. Plants can absorb CO 2 gas through the process of photosynthesis by the formula: 6 mol + 12 mol O 1 mol + 6 mol + 6 mol O.
The ability of plants to absorb bgas varies. According to Prasetyo et al, forests that have different types of vegetation have a different ability or absorption to [17]. Absorption of various types of vegetation to CO 2 can be seen in table 2: Source: [15] 3 Methodology This method refers to the scientific research conducted by Philipi de Rozari and Suwari [19]. The research uses quantitative descriptive method, ie problem-solving procedure that is investigated by describing or describing the state of the current research object based on facts that appear or as it is in quantitative way. The research stages include (1) determining the condition of existing CO2 emissions and estimation of CO2 concentration in the future,(2) identification of forest constituent tree species, (3) analysis of CO2 (carbon sink absorption by various forms of green open space (RTH) of urban forest, and (4) determining the amount of urban forest area requirement as CO2absorber. Research conducted in the city of Semarang is in Forest City Tinjomoyo.

Materials and tools
The materials used in this study were leaf samples, aquadest, HCl, NaOH, Ba(OH)2, alcohol, reagent Cu, red phenols, Nelson reagents, ZnSO4, filter paper, cutex, RTRW and green open space Semarang city.
The equipment used in the study includes: a set of glassware for chemical analysis, analytical balance, water bath, mortar, porcelain cup, oven, and Cecil spectrophotometer.

Data collection
The data used in this study consists of primary data and secondary data. Primary data collection was conducted through field surveys and laboratory analysis. Secondary data are obtained from various related institutions and literature tracking, such as research results and other relevant scientific documentation. Secondary data collected include population, electricity consumption, fuel oil and gas consumption in Semarang City.

Data analysis
The levels of anthropogenic CO2 emissions sourced from electricity consumption and the use of fuel oil and gas were analyzed using CO2 emission factor values established by the Energy Information Administration (EIA) 2000, DEFRA (2001) and The National Energy. Foundation (NEF) in 2005, while CO2 absorption by various plants was analyzed by carbohydrate measurement method [16]. Detail of analysis method as follow: 1) CO2 emissions from electricity consumption. The approach used to determine CO2 emissions from electricity consumption is based on the amount of electricity consumption in Semarang City and emission factor CO2. Total emissionsCO2 is calculated from electricity consumption / year of observation multiplied by emission factor(gram CO2/kWh). The value of the emission factor is the value of CO2 emissions from Electricity consumption set by the Energy Information Administration (2000), which is gram CO2/kWh. The total value of emissions is the total CO2 emissions resulting from the use of electrical energy.

2) CO2 emissions from Premium Consumption
The calculation of CO2 emissions from premium / gasoline is done through the approach of the amount of consumption and the value of emission factor.

3) CO2 emissions from solar consumption
The amount of CO2 emissions from diesel consumption is calculated based on total diesel fuel consumption multiplied by CO2 emission factor from diesel consumption set by The National Energy Foundation (2005),

4) CO2 Emissions from Kerosene Consumption
The determination ofCO2 emissions from the use of kerosene in Semarang City is based on kerosene consumption multiplied by kerosene emission factor.

5) CO2 Emissions from Fuel Gas Consumption
The amount ofCO2 emissions from gas fuel consumption is calculated based on the total consumption of gas fuel (BBG) multiplied by CO2 emission factor from diesel consumption set by The National Energy Foundation (2005),

6) Need for BBMG and Prediction of Future Needs
The data used is the data of the use of fuel oil and gas

Discussion
Urban forest is need to absorb the anthropogenic CO 2 gas emissions. This study proposed the formula to account and analyze the needs of the forest area City as an anthropogenic CO 2 absorber Used. This formula is use to assess the parameter oil gas such as gasoline, diesel, kerosene and LPG. The urban forest formula not yet account for the oxygen need for human life in cities. This formula could not be use directly to design the area of urban forest since the parameter of urban forest need should accommodate many function, such as, social, economic, ecology, psychology, amenity and leisure.

Conclusions
Anthropogenic CO 2 gas emissions increase every year. This is due to the increasing demand for fuel oil and gas as the population increases. Each tree has a different absorption of carbon dioxide gas depending on the leaf area per tree and the absorption of CO 2 per cm 2 . Trees that have CO 2 gas absorption. The addition of urban forest area to minimize the increase of anthropogenic CO 2 gas in Semarang City