Abstract
Managers at Glacier Bay National Park must annually determine the allowable number of cruise-ship entries into the park. This decision considers how differences in visitor volume may affect park resources. This study quantified the impacts to air quality and visibility under different ship quotas using simulations with the Weather Research and Forecasting model inline coupled with chemistry. Results of the simulation assuming two entries per day for May 15 to September 15, 2008 (QTA; 248 ship entries representing a 35% increase) were compared to those of the 2008 cruise-ship activity (REF; 184) during that timeframe. A simulation without anthropogenic emissions (CLN) served to assess the overall impacts of cruise-ship emissions on visibility and air quality in Glacier Bay. Compared to REF, the increased entry quotas shifted chemical regimes and aerosol composition, depending upon thermodynamical conditions, and ambient concentrations. On days with notable regime shifts, sulfur-dioxide concentrations deceased while ammonium-sulfate aerosol concentrations increased. The increased quotas also altered the fine-to-coarse aerosol ratios in both directions despite constant ratio of fine-to-coarse aerosol emissions. In Glacier Bay, the days with worst visibility coincided with high relative humidity, although this relationship varied by scenario. On the 20% worst days, mean visibility was slightly better in CLN (mean haze index over Glacier Bay waters = 2.9 dv) than in REF ( = 3.1 dv). While increased emissions in QTA reduced mean visibility by 0.1 dv, the 10th, 50th and 90th percentile of haze indices remained identical to those in REF. Best (worst) visibility occurred on the same days in REF and QTA due to emission impacts, but on different days than in CLN because relative humidity solely governed visibility in CLN. While calm wind played no role for visibility in CLN, wind speed gained similar importance for visibility as relative humidity in REF and QTA. Overall, increasing ship quotas would only marginally affect air quality and visibility as compared to REF, although even small changes in these parameters need careful consideration in the context of conserving the values of Glacier Bay.
Highlights
The demand for glacier viewing is likely to increase as “last chance” tourism highlights the need to see sensitive places before they disappear [1]
Concentrations on days without emissions in Glacier Bay in reference simulation (REF) were by a factor of 12.2, 2.5, 1.4 2.2, 1.2, and 1.4 higher for PM10, PM2.5, SO2, NO2, peroxiacetyl nitrate (PAN), and volatile organic compounds (VOC) than in CLN, while O3 concentrations remained about the same. These findings suggest that cruise-ship emissions from previous days, along with formation of secondary particulate matter (PM) from precursors (NO, SO2, NH3) caused the on average 1.5 dv higher haze index in REF on cruise-free days as compared to CLN (Figure 4, Figure 7)
Together these findings indicate that while ship emissions contributed to degraded visibility in REF and QTA in Glacier Bay, meteorology primarily governed visibility
Summary
The demand for glacier viewing is likely to increase as “last chance” tourism highlights the need to see sensitive places before they disappear [1]. Glacier Bay National Park is a coveted destination to view a number of active tidewater glaciers and receives high demand for access. The National Park Service (NPS) has a mandate to both conserve park resources while providing for appropriate opportunities for visitation. The NPS manages parks to “...preserve unimpaired the natural and cultural resources and values of the national park system for the enjoyment, education, and inspiration of this and future generations” [2]. In 2015, over 95% of all visitors to Glacier Bay arrived aboard cruise ships. Increases in cruise ships equate to more opportunities for enjoying park resources and mean elevated emissions, which affect both air quality and visibility
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