The regional influence of volcanic emissions from Popocatéptl, Mexico: Discussion of “Measurement of aerosol particles, gases and flux radiation in the Pico de Orizaba Nacional Park, and its relationship to air pollution transport”, Márquez et al., 2005, Atmospheric Environment, 39, 3877–3890

Abstract

An understanding of the influence of anthropogenic and natural point sources of pollution on the compositions of distant airmasses requires the careful collection of atmospheric composition data over extended periods of time. Equally, a proper understanding of the influence of megacities, biomass burning plumes and persistent volcanic emissions on the oxidising capacity of the atmosphere requires analysis of the downstream fate of their associated gas and aerosol plumes. Marquez et al. (2005) recently presented some interesting data on the compositions of ambient atmospheric gases and particles at a sampling site in Mexico (Pico de Orizaba National Park, elevation 3300 m; Fig. 1) in late February and early March 2001. Two notable features of their data were the high concentrations of SO2 (mean value 14 ppb) and particulate sulphate (mean 5 μg m−3). The authors ascribed these features to the arrival of air from urban sources nearby, either Mexico City (200 km to the west, elevation 2240 m) or Puebla City (70 km to the west, elevation 2160 m). However, airmass parcels which arrive at the sampling location from either Mexico City, or Puebla, are likely to have passed close to the active volcano of Popocatepetl, 160 km from the sampling endpoint (Fig. 1). In their original paper, Marquez et al. (2005) dismissed any possible volcanic influence on their sampling on the basis of the absence of any volcanic (ash) plume visible in AVHRR weather satellite data. However, Popocatepetl, like many volcanoes, is a prodigious source of reactive gas and aerosol even in the absence of any visible ash plumes. ‘Passively’ degassing volcanoes are becoming increasingly well known as major contributors to the tropospheric gas and aerosol burden, and in particular that of SO2, sulphate and other particles