Hypotheses, expected signs, and interpretations for the PM2.5 model
| Hypothesis | Expected sign | Interpretation |
|---|---|---|
| H1a: β1 > 0 | Positive | As built-up area (BU) expands, PM2.5 levels are expected to increase. This is because urban sprawl often naturally increases traffic, energy use, and emission-producing activities |
| H1b: β2 < 0 | Negative | As forest area share (FOR) increases, PM2.5 is expected to decrease. The main reason for this is the capacity of natural vegetation to capture/remove particles from the air and more general regulatory ecosystem services |
| H1c (core): β3 < 0 | Negative | As FOR increases, the negative impact of urbanization (BU) on PM2.5 is expected to weaken. In other words, in places with high FOR, the slope of the BU–PM2.5 relationship should be lower than expected |
| H1d: β4 < 0 | Negative | As per capita income rises, PM2.5 levels are expected to decline. This is because higher income accelerates the transition to cleaner technologies. In most cases, tighter environmental controls during the economic development process also facilitate this transition |
| H1e: β5 ≥ 0 | Positive or weakly positive | A higher urban population share (URB) tends to increase PM2.5 levels due to concentrated human and economic activity |
| H1f: β6 ? | Ambiguous | The effect of arable land (ARB) on PM2.5 emissions is uncertain: depending on agricultural practices, it may increase or decrease PM2.5 emissions |
| Hypothesis | Expected sign | Interpretation |
|---|---|---|
| H1a: β1 > 0 | Positive | As built-up area (BU) expands, PM2.5 levels are expected to increase. This is because urban sprawl often naturally increases traffic, energy use, and emission-producing activities |
| H1b: β2 < 0 | Negative | As forest area share (FOR) increases, PM2.5 is expected to decrease. The main reason for this is the capacity of natural vegetation to capture/remove particles from the air and more general regulatory ecosystem services |
| H1c (core): β3 < 0 | Negative | As FOR increases, the negative impact of urbanization (BU) on PM2.5 is expected to weaken. In other words, in places with high FOR, the slope of the BU–PM2.5 relationship should be lower than expected |
| H1d: β4 < 0 | Negative | As per capita income rises, PM2.5 levels are expected to decline. This is because higher income accelerates the transition to cleaner technologies. In most cases, tighter environmental controls during the economic development process also facilitate this transition |
| H1e: β5 ≥ 0 | Positive or weakly positive | A higher urban population share (URB) tends to increase PM2.5 levels due to concentrated human and economic activity |
| H1f: β6 ? | Ambiguous | The effect of arable land (ARB) on PM2.5 emissions is uncertain: depending on agricultural practices, it may increase or decrease PM2.5 emissions |