1. positive.
2. the dropping oil price may lead to a competitive market. if so, under this situation, it gives an incentive to the development of technology innovation in energy, particularly the renewable energy which generates little emission. also, in this century, as era of technology explosion, it is more likely that the renewable energy will gradually replace the traditional energy (oil, coal mainly) in the long run. that would cause that the oil price will go down in order to achieve more consumption, thereby increasing the income of oil companies.
3. psychologically speaking, people usually focus on the things that are harder to contain, but would give an ignorance or less concerns to 'the too-cheap-or-free' products. in the MASLOW HIERARCHY THEORY additionally, consumers probably will to buy the products with a higher price in order to capture the top of pyramid, or called self-esteem or self-actualisation (eventually to some extent, it is showing off

). because logically most of consumers will consider that high price usually with a high level of quality. in the other word, lower oil price enables customers to think that the quality of oil may has been lowered. and for an instance, to drivers, especially the drivers who look their cars as babies, would say 'low quality will harm my baby'. then, drivers will possibly lessen frequency of using cars, reducing the volume of exhaust emission, or even climate changes. that is really helpful to environment.
to summarise, a decrease of oil price is more likely to reduce the using of oil, and it also will provide a positive competitive market which could stimulate advancement of technology of renewable energy. all of these will benefit environment.