**2. Materials and methods**

The emissions and energy associated with the agricultural burnings depend on many parameters; for that, those supported by current and reliable information were selected. The settings used to feed the model are the following:

The lower heating value of the wheat straw was considered as 14.50 MJ/kg, which was experimentally determined. The tests were realized with the *T. aestivum* wheat variety from Baja

**Year Wheat-harvested surface (ha) Year Wheat-harvested surface (ha)**

 53,098 2002 74,394 50,572 2003 85,320 48,374 2004 80,555 60,366 2005 75,989 79,683 2006 79,946 79,683 2007 81,958 80,018 2008 88,937 69,658 2009 87,724 53,159 2010 87,321 67,224 2011 74,260 54,913 2012 72,153 50,636 2013 83,015 74,273 2014 81,681 68,033 2015 90,609

 **emission factors by agricultural burning technique**

open air, the factors reported by the EPA AP-42 [17], enlisted in **Table 2**, were used. Such report clusters the emission factors according to the incineration technique used by the farmers. It is important to note that in the Mexicali Valley case, both techniques are used by producers, for which the calculations were made considering the two of them. The incinerating

• Backfire: Burning technique in which the fire advances to the opposite direction of the

**Figure 4** displays the sequence and relationships between the parameters used in the emis-

emissions, generated by wheat straw burnt *in situ* in the

Wheat Straw Open Burning: Emissions and Impact on Climate Change

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71

California, Mexico [14].

2001 64,926

**2.3. PM, CO, and CH4**

wind.

sions and energy model.

To estimate the PM, CO, and CH4

techniques according to the EPA are described as follows:

**Table 1.** Historical series of the wheat-harvested surface, 1987–2015.

• Headfire: Burning technique where the fire advances in the wind direction;

**2.4. Parameters used in the emissions and energy model and sequence**


#### **2.1. Historical series of the wheat-harvested surface**

Wheat straw is a waste generated in large quantities during wheat harvesting. To estimate its generation in the Mexicali Valley, information on the annual wheat harvested surface on the 1987–2015 period was used and is presented in **Table 1** [15, 16].

#### **2.2. Wheat straw generation index and lower heating value**

To estimate the quantity of wheat straw generated by agricultural cycle, a generation index of 7.3 t/ha was considered [6].

Wheat Straw Open Burning: Emissions and Impact on Climate Change http://dx.doi.org/10.5772/intechopen.76031 71


**Table 1.** Historical series of the wheat-harvested surface, 1987–2015.

are the low density of biomass, handling and high transportation cost, an attractive heating

**Figure 3.** Open burning of the wheat straw near the rural population of the Mexicali Valley, Mexico.

In this chapter, the emissions caused by the headfire or backfire burning of wheat straw *T. aestivum* in Baja California, Mexico, for the period 1987–2015, were estimated through the development of a model on the iThink® dynamic simulator [13]. Also, the energy emitted by wheat straw burning was calculated considering its significant heating value of 14.50 MJ/kg

The emissions and energy associated with the agricultural burnings depend on many parameters; for that, those supported by current and reliable information were selected. The settings

emission factors by agricultural burning technique.

Wheat straw is a waste generated in large quantities during wheat harvesting. To estimate its generation in the Mexicali Valley, information on the annual wheat harvested surface on the

To estimate the quantity of wheat straw generated by agricultural cycle, a generation index of

value, and the physicochemical characterization [12].

**2. Materials and methods**

70 Global Wheat Production

used to feed the model are the following:

**2.** Wheat straw generation index, **3.** Wheat straw lower heating value,

**4.** PM, CO, and CH4

7.3 t/ha was considered [6].

**1.** Historical series of the wheat harvested surface,

**2.1. Historical series of the wheat-harvested surface**

1987–2015 period was used and is presented in **Table 1** [15, 16].

**2.2. Wheat straw generation index and lower heating value**

determined experimentally [14], and it was included in this model.

The lower heating value of the wheat straw was considered as 14.50 MJ/kg, which was experimentally determined. The tests were realized with the *T. aestivum* wheat variety from Baja California, Mexico [14].

#### **2.3. PM, CO, and CH4 emission factors by agricultural burning technique**

To estimate the PM, CO, and CH4 emissions, generated by wheat straw burnt *in situ* in the open air, the factors reported by the EPA AP-42 [17], enlisted in **Table 2**, were used. Such report clusters the emission factors according to the incineration technique used by the farmers. It is important to note that in the Mexicali Valley case, both techniques are used by producers, for which the calculations were made considering the two of them. The incinerating techniques according to the EPA are described as follows:


#### **2.4. Parameters used in the emissions and energy model and sequence**

**Figure 4** displays the sequence and relationships between the parameters used in the emissions and energy model.

#### 72 Global Wheat Production


**2.5. Emissions and energy model**

under study and associated emissions.

**3. Discussion and results**

CH<sup>4</sup>

combustion.

1987–2015.

and 12.41 kg CH4

Based on the selected parameters and with the purpose of facilitating the analysis of the emissions associated with wheat straw burning during the 1987–2015 period, a dynamic model was developed on iThink®, whose simplified version is illustrated in **Figure 5**. The development of the model allows to establish and observe practically and graphically the interrelations of the different variables used to estimate the emissions corresponding to wheat straw burning and the quantity of energy generated during the combustion of the agricultural waste

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73

The simulation results indicate that for headfire burning, the annual emissions (PM, CO, and

**Figures 6** and **7** illustrate the accumulated emissions of the period under study. In the head-

The decrease of emission in backfire burning is due to a more significant interaction generated between the wheat straw and the oxygen present in the air because the incineration occurs against the wind which promotes the slow burning of wheat straw and better

The energy sent to the environment by wheat straw incineration in the 1987–2015 period was estimated at 188.81 PJ, which represents the 2.29% of the primary energy production of Mexico by 2015 [18]. During the analyzed period, there was an increase in the energy sent to the environment that varied from 4.78 PJ in 1987 to 8.15 PJ in 2015. **Figure 8** displays the behavior of the accumulated values of the energy sent to the environment in

The annual average of discarded energy in the 1987–2015 period was of 6.51 PJ, which represents the 1.81% of the biomass energy in Mexico, 2015 [18]. However, the use of this wasted energy presents some challenges and opportunities that must be taken into consideration,

**Figure 9** displays the matter and energy balance corresponding to one wheat hectare harvested in the Mexicali Valley, where the index of wheat production by hectare is of 6.46 t and the generation of wheat straw is 7.3 t. The 15% of wheat straw generated has many applications such as incorporation in agricultural soil, cattle food, construction material elaboration, among others. The 85% of wheat straw, that is to say, 6.205 tons, is openly burnt *in situ*, which represents 89,972.50 MJ of energy sent to the environment and causes pollutant emissions. In the headfire burning, 477.78 kg of contaminants, composed of 68.26 kg PM, 397.12 kg CO,

, are generated. In the case of backfire burning, 390.37 kg of contaminants,

which implies evaluating the technical and economic feasibility of any process.

composed of 37.23 kg PM, 335.07 kg CO, and 8.07 de CH4, are generated.

from 20,197 t (1987) to 34,465 t (2015), which represents an increase of 71%.

burning, the emissions are 77,428 t of PM, 696,853 t of CO, and 16,776 t of CH4

fire burning, 141,951 t of PM, 825,899 t of CO, and 25,809 t of CH4

) increased from 25,370 t (1987) to 43,292 t (2015). While for backfire, the emissions went

are generated. In the backfire

.

**Table 2.** Emissions factors.

**Figure 4.** Parameters used in the emissions and energy model.

**Figure 5.** Emissions and energy model developed in iThink®.
