In Chile, 60% of its population are exposed to levels of Particulate Matter (PM) above international standards
. Air Pollution is causing 4,000 premature deaths per year
, including health costs over US$8 billion.
The System Dynamics Causal Loop Diagram developed herein shows an initial study of the dynamics among the variables that influences the accumulation of PM in the air, in particular the case of Temuco, in the South of Chile. In Temuco, 97% of the PM inventories comes from the combustion of low quality firewood, which in turns is being burned due to its low price and cultural habits/tradition.
The Model starts with the concept of closing the [Temperature GAP]
between the [Ambient Temperature]
and the [House Internal Temperature]
. The monetary resources come from the [Family Budget]
, which in turn needs to be distributed between [Fraction of Budget for Heating]
and [Fraction of Budget for House Insulation]
Both [Heating] and [Insulation] have balancing feedback loops associated with [Budget Limits]: as the [Family Budget] goes up, the [Fraction of Budget for heating/insulation] goes up, increasing the [Costs], reducing the [Family Budget], thus reducing the [Fraction of Budget for heating/insulation].
From the diagram above it can be seen that the decision to increase the [Fraction of Budget for House Insulation] is affected by time delays (i.e. it would require major investment end effort). Additionally, the actual physical tasks associated with the increase in [House Insulation Level] add another delay to the insulation solution. Thus, in the short-term, it is easy to see why it is more attractive to increase the [Fraction of Budget for Heating] (i.e. to directly buy firewood for combustion) instead of increasing the [Fraction of Budget for House Insulation].
Both alternatives have feedback loops associated with their effectiveness: as the [House Insulation Level] goes up, the [House Internal Temperature] goes up, reducing the [Temperature GAP], thus reducing the [Fraction of Budget for House Insulation], reducing the likelihood of increase further the [House Insulation Level]. An analogous process can be deducted within the [Heating Reduction] balancing feedback loop.
The [Fraction of Budget for Heating] can be spent in increasing the [Stock of Heating Equipment] and/or increasing the [Heating Efficiency] of the heaters. Both alternatives show [Delays] associated with their implementation related to the additional time and budget required in comparison with the option to directly investing in [Firewood Stock].
The [PM Emissions]
are a function of the amount of [Firewood Stock]
burned, their [Firewood Quality]
(i.e. high humidity leads to higher emissions), the [Stock of Heating Equipment]
and their [Heating Efficiency]
Thus, an increase in [Firewood Quality]
will lead to an increase in the [Heat Generated]
but also to a reduction in [PM Emissions]
. Furthermore, studies have shown that, even spending more in order to increase the [Firewood Quality]
(i.e. dry firewood), the monthly total [Costs]
of heating are reduced due to the higher combustion efficiency of the high-quality firewood. Then, if investing in [Firewood Quality]
is cheaper and evironmentally friendlier, why almost all the city's population continue to using it?
Mainly because cultural habits and tradition.
Then, what influence could this [Cultural Persistance]
have in the [PM Emissions]
The answer to this question lies in the cultural tendency to continue selecting low [Firewood Quality] due to its low price, due to tradition (i.e. to see smoke during combustion) and due biases in the social class. In order to account this effect in the model, the variable [Cultural Persistance Firewood Combustion] was added.
The rationale behind this is as follows: As the [Firewood Stock] goes up (i.e. mix between high and low quality firewood), the [Heat Generated] goes up (i.e. more fuel to burn), reinforcing the idea that "firewood works" as a fuel for heating, increasing further the [Cultural Persistance Firewood Combustion]. The impacts of this rationale are direct and quantifiable, without delays in the process, represented as the [Low Quality Firewood Persistance] reinforcing feedback loop.
On the other hand, as the [Cultural Persistance Firewood Combustion] increases, the [Firewood Quality] is being reduced, increasing total [PM missions], creating [Health Impacts due to emissions]. In the long run and after long [Delays], more [Health Impacts due to emissions] will lead to a reduced [Cultural Persistance Firewood Combustion], creating the balancing feedback loop [Firewood Quality] that counters the effect of the reinforcing feedback loop generated by Low Quality Firewood usage.
An analogous effect can be seen in the [Equipment Renewal] - [Equipment Persistance] feedback loops shown below.
It is important to note that the feedback loop of reduction in [Cultural Persistance Firewood Combustion/Old Equipment] caused by [Health Impacts due to emissions] is very, very weak. People don't draw a causal link between respiratory diseases and the [Firewood Quality] and/or [Heater Efficiency] because it is difficult to relate the consequences of the actions on these two variables to health issues mainly due to the huge time [Delays] in involved in this process.
Then, what can be concluded from the analysis described in this model?
First, from the budgetary perspective, it is more simple and direct just to buy firewood, because investing in house insulation and heater efficiency have time delays within their processes. The consequences of this reasoning is that people will tend to buy and burn firewood as the primary mechanism of house heating.
Second, through analyzing the fact that the cost of high quality (dry) firewood is higher and the overall cost of using dry firewood is lower (due to better combustion efficiency), one can conclude that people would tend to use dry firewood, but that is not the case. There are important cultural influences that need to be taken into account. These cultural influences reinforces the idea to keep using low quality (high humidity) firewood and to keep using old heaters, not only because they "work", but also because it has been the social habit during decades.
Third, the reinforncing feedback loops that describe the cultural persistance are really strong in comparison to the balancing feedback loops that reduces the likelihood of using low quality firewood / low efficiency heaters due to health impacts, mainly because of the time delays inherent to this process.
Finally, it can be concluded that any public policy designed to reduce PM emissions should include dynamics analyses of people's behavior, because, as we have learned throughout the modern history, human beings are not as rational as we think we are.