**3. Discussion and results**

The simulation results indicate that for headfire burning, the annual emissions (PM, CO, and CH<sup>4</sup> ) increased from 25,370 t (1987) to 43,292 t (2015). While for backfire, the emissions went from 20,197 t (1987) to 34,465 t (2015), which represents an increase of 71%.

**Figures 6** and **7** illustrate the accumulated emissions of the period under study. In the headfire burning, 141,951 t of PM, 825,899 t of CO, and 25,809 t of CH4 are generated. In the backfire burning, the emissions are 77,428 t of PM, 696,853 t of CO, and 16,776 t of CH4 .

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 combustion.

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 1987–2015.

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

**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, and 12.41 kg CH4 , are generated. In the case of backfire burning, 390.37 kg of contaminants, composed of 37.23 kg PM, 335.07 kg CO, and 8.07 de CH4, are generated.

**Figure 6.** Accumulated emissions by headfire burning.

**Figure 7.** Accumulated emissions by backfire burning.

The balance of energy and matter indicates that for each ton of harvested wheat in the Mexicali Valley, 1,130.03 kg of wheat straw are generated, of which 169.50 kg are used in diverse applications and 960.53 kg are burnt in open air. The incineration of this waste implies that 13,927.63 MJ are wasted without any use, as well as pollutant emissions. In the headfire burning, 73.96 kg of pollutants, composed of 10.57 kg PM, 61.47 kg CO, and 1.92 kg CH4, are generated. As for the backfire burning, 58.88 kg of contaminants, composed of 5.76 kg PM, 51.87 kg CO, and 1.25 kg CH4 , are generated.

**4. Conclusions**

**Figure 8.** Energy sent to the environment.

Wheat cultivation is an intensive activity of great importance for the economic development of Baja California, Mexico. It also means the generation of vast amounts of wheat straw that is

Since 1987 until 2015, the sown surface of wheat has incremented in the Mexicali Valley,

annually, contaminants that affect

Wheat Straw Open Burning: Emissions and Impact on Climate Change

http://dx.doi.org/10.5772/intechopen.76031

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burnt *in situ* and emits large quantities of PM, CO, and CH4

**Figure 9.** Material and energy balance of one harvested hectare of wheat.

resulting in an increase in the polluting emissions and the wasted energy.

the air quality of Mexicali and its valley.

**Figure 8.** Energy sent to the environment.

**Figure 9.** Material and energy balance of one harvested hectare of wheat.
