Does "at risk" refer to "at risk of exposure to air pollution" or "at risk of natural death"?

A significantly increased hazard ratio (HR) for PM2·5 of 1·07 (95% CI 1·02—1·13) per 5 μg/m3 was recorded.

Would anyone like to explain the meaning of "of 1·07" in that context? What does 1.07 refer to?

http://www.epa.gov/pm/

"Particulate matter," also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.

The size of particles is directly linked to their potential for causing health problems. EPA is concerned about particles that are 10 micrometers in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects. EPA groups particle pollution into two categories:

"Inhalable coarse particles," such as those found near roadways and dusty industries, are larger than 2.5 micrometers and smaller than 10 micrometers in diameter.

"Fine particles," such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller. These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air.
Basic Information - Basics about particle pollution.

Health - Effects of particle p

We used data from 22 European cohort studies, which created a total study population of 367 251 participants. All cohorts were general population samples, although some were restricted to one sex only. With a strictly standardised protocol, we assessed residential exposure to air pollutants as annual average concentrations of particulate matter (PM) with diameters of less than 2·5 μm (PM2·5), less than 10 μm (PM10), and between 10 μm and 2·5 μm (PMcoarse), PM2.5 absorbance, and annual average concentrations of nitrogen oxides (NO2 and NOx), with land use regression models. We also investigated two traffic intensity variables—traffic intensity on the nearest road (vehicles per day) and total traffic load on all major roads within a 100 m buffer. We did cohort-specific statistical analyses using confounder models with increasing adjustment for confounder variables, and Cox proportional hazards models with a common protocol. We obtained pooled effect estimates through a random-effects meta-analysis.

BTW, I wonder the difference between "a standardised protocol" and "a common protocol."

Quote:

BTW, I wonder the difference between "a standardised protocol" and "a common protocol."

LOL you are overworking me so if you will forgive me I will leave that question to someone else who hopefully will have a far better background in such studies then a poor electrical engineer, who college days are forty years in the past, happen to have.