# Investigation into the Effect of Atmospheric
## 5 Conclusions  
The Global Satellite Navigation System (GNSS) has been widely used in vehicle and personal navigation, engineering and geodetic surveying, geophysical and geodynamic studies, machine guidance, attitude determination, indoor positioning (with high-sensitivity receiver), etc. High-precision GNSS applications such as engineering and geodetic surveying need millimeter and centimeter level accuracy. Air pollution is a serious environmental problem globally, especially in developing countries. Major pollutants include sulfur oxides, nitrogen oxides, carbon monoxide, volatile organic compounds, particulate matter (PM), chloroform, ammonia, radioactive pollutants, etc. GPS signals travel through the atmosphere before arriving at receivers on the Earth's surface, but are GPS signals affected by the increased concentration of the PM\({}_{2.5}\)/PM\({}_{10}\) particles? There is no standard model of the effect of PM\({}_{2.5}\)/PM\({}_{10}\) particles on GNSS signals in GPS data processing, although an approximate generic model of non-gaseous atmospheric constituents (<1 mm) can be found in the literature. Through knowing the unique condition of repeatable satellite geometry of GPS in about one sidereal day at continuous static antennas, this paper presented an empirical method to investigate the impact of PM\({}_{2.5}\)/PM\({}_{10}\) particles and their concentrations on GPS signal propagation. The method was used to compare the carrier-to-noise ratios (CNRs) in two consecutive sidereal days with similar and very different PM indices. Six data sets were collected on the campus of the University of Nottingham Ningbo China in November 2014 and December 2015 for this investigation. Since the receiver clock offset of a GNSS receiver is not a constant, we cannot compare GNSS pseudorange and carrier-phase measurements collected in high and low PM periods directly. Moreover, relative positioning techniques cannot be used to detect the impact of particulate matter on GNSS signal propagation because the assumption of differenced residuals due to particulate matter in different atmospheric paths cannot be justified. CNR is not affected by the different receiver clock offsets at different measurement epochs and it is not affected by multipath effect when the same sidereal time is used in the comparison. Therefore, CNR is used in this investigation.  
In the CNR test, the results are mixed, but with more negative results than positive results (i.e., reduced CNR due to the presence of PM\({}_{2.5}\)/PM\({}_{10}\) particles). All the CNR differences are much less than 1 dBHz, which is much less significant than the multipath effect. The CNR differences between consecutive sidereal days are likely due to the GPS carrier-phase measurement noise. Therefore, we cannot find any significant impact of high PM\({}_{2.5}\)/PM\({}_{10}\) concentration on GPS signal propagation with the presented empirical method and the six data sets collected. This result agrees with the computed delays from the approximate generic model.  
The authors would like to thank the reviewers for their in depth reviews and helpful suggestions that have greatly contributed to improving this paper. Part of the Article Processing Charge (APC) is funded by the Zhejiang Natural Science Foundation (ZJNSF) General Programme grant LY17D040001.  
[PERSON] conceived and designed the experiments, performed the experiments, analyzed the data, and wrote the paper; [PERSON] contributed PM, AQI and meteorological data.  
The authors declare no conflict of interest.