Effects Of Surface Fire Behavior On Emission From Pinus Koraiensis Plantation–A Laboratory Simulation Study

The mountainous area in the eastern part of northeastern China is important state owned forest areas,and red pine（Pinus koraiensis）is the zonal apex vegetation and the main silvicultural species in this region.Because of the high flammability and high forest fire risk of red pine,its plantation forest is the key forest fire prevention area in this region.Particulate and gaseous pollutants are important components of forest fire smoke,and the emissions of carbon-containing particulate matter and gaseous pollutants can seriously affect the"carbon sinks"of forest,and high-intensity forest fires can even cause transient forest"carbon imbalance".Meanwhile,the emission of smoke from forest fires not only affects short-term respiration health of fire fighter and public,but also poses a long-term threat to human cardiopulmonary functionality.Forest fire behavior,as a phenotypic phenomenon of forest combustion,is necessarily linked to smoke emission from forest fires.The study of forest fire smoke emission patterns under the change of forest fire behavior is important for revealing the mechanism of forest fire smoke emission,improving the efficiency of forest firefighting,reducing the casualties and forest resources loss,and promoting"carbon sink"with"emission reduction"to achieve the goal of"double carbon",which is of great ecological,economic and social significance.This study was conducted in the Maoer Mountain area which located in the eastern mountainous region of Northeast China,and red pine plantations with high flammability and weak resistance to natural hazards were selected for the study.The dead surface fuel of red pine plantation forest were collected as experimental materials,and the characteristics of forest fire behavior and the emission characteristics of particulate pollutants and gaseous pollutants during forest combustion were measured by laboratory simulated combustion experiments under field conditions as the main research means.In this study,we systematically investigated the effects of forest fire behavior characteristics on the respirable particulate matter and mixed exposure ratio,and established a forest fire smoke prediction method based on easily estimated fire behavior characteristics.The main innovation of this study is to investigate the relationship between forest fire behavior characteristics and forest fire smoke emission,and predict the hazardous fire enviroment above the smoke exposure limit.The results will provide basic data for quantifying changes in forest fire behavior and forest fire smoke characteristics under changes in different influence factors,and will provide guiding suggestions and scientific basis for immediate smoke prediction in firefighting environment and development of firefighting techniques and tactics.The main results are as follows:（1）In terms of influence factors on the forest fire behavior characteristics,the effect of wind speed on the forest fires behavior characteristics was highly significant（P<0.001）,except for residence time and flame height,which were significantly（P<0.001）inhibited,and other forest fires behavior characteristics,which were significantly promoted;the most sensitive responses to changes in fuel loadings are flame height（P<0.001）,fuel consumption loading and combustion efficiency,with significant effects on other fire behavior characteristics as well;the fuel moisture content has the most significant（P<0.001）effect on flame height,and also shows a significant inhibitory effect on some forest fire behavior characteristics;the interaction of wind speed and fuel moisture content has a highly significant（P<0.01）effect on the spread rate;the interaction between wind speed and fuel loading also has a highly significant（P<0.01）effect on fuel consumption loading,the higher the wind speed and fuel loading,the higher the fuel consumption loading caused by the interaction between the two factors;（2）PM_2.5 concentration(range:569.20～7 268.10μg·m^-3)is highly significantly（P<0.001）and positively correlated under the influence of single factor of wind speed,fuel moisture content and fuel loading;the interaction of factors also has a significant or highly significant effect on PM_2.5 concentrations,especially at low wind speeds,where the interaction of fuel moisture content and fuel loading has a significant（P<0.001）effect on PM_2.5concentrations,with both wind speed and fuel loadings playing a dominant role in PM_2.5concentrations;the effect of high fuel moisture content on the PM_2.5 concentration released by combustion is more complex;（3）The maximum of combustion release CO,CO₂ and NO_X SO₂ concentrations are 89.77mg·m^-3、29 094.07 mg·m^-3、1.13 mg·m^-3and 0.14 mg·m^-3;wind speed has a highly significant（P<0.01）effect on the combustion release of CO,CO₂ and NO_X concentrations,but not on the SO₂ concentration（P>0.05）;the effect of fuel loading on CO₂ is highly significant（P<0.01）,and the effect of fuel loading and fuel moisture content on the concentration of the remaining gaseous pollutants is not significant（P>0.05）;based on the interaction analysis of factors,the effects on CO and CO₂ concentrations are,from largest to smallest,fuel loading>wind speed>fuel moisture content.the influence factors under interaction have no significant effect on NO_X and SO₂ concentrations;the maximum concentrations of NO_X and SO₂,are well below the exposure gas concentration limit value(10 mg·m^-3)specified in the Standard,so NO_X and SO₂ will not be studied in depth in the subsequent study of fire experiment smoke prediction in firefighting;（4）Flame length,depth,fuel consumption loading and fire line intensity are highly significant positive correlation with PM_2.5 concentration;flame length and fuel consumption loading are highly significant positive correlation with CO concentration;residence time,flame height,fuel consumption loading and CO₂ concentration are highly significant positive correlation;when wind speed is greater than 0,flame angle and PM_2.5 concentration,CO concentration and CO₂ concentration are all negatively correlated,which is caused by the high spread rate and less fuel involved in combustion.（5）Based on MLR,SVM,BPNN and RF,forest fire smoke exposure characteristics were predicted using easily estimated forest fire behavior characteristics,and RF was the optimal algorithm after screening,the R² of predicting PM_2.5 concentration and MER were 0.88 and0.87,and MAPE were 16.55%and 14.84%,;flame length had the most significant effect on PM_2.5 and MER based on RDA,and the flame length explained 15.0%and contributed42.6%to smoke exposure;when the concentration of particle pollutant and gaseous pollutant MER were exceeded limit values,the corresponding flame lengths were 28.30 cm and 20.88cm,respectively,and when the flame length exceeded the limit value,attention should be paid to forest fire smoke protection.In summary,the forest fire behavior characteristics measured in this study were highly correlated with the collected forest fire smoke concentrations,making it possible to realize fire environment smoke predictions based on forest fire behavior characteristics.This study presents and validates the underlying assumptions for smoke prediction in the fire environment based on preliminary analysis at the laboratory combustion experiment only.Further optimization of laboratory data parameters using actual forest combustion data in the field will significantly improve the applicability of indoor burning experiments.Combined with the large-scale forest fire spread simulation analysis,it will help scientific formulation of forest fire prevention policies and effectively improve the forest firefighting efficiency.