Tethered balloon-based soundings of ozone, aerosols, and solar radiation near Mexico City during MIRAGE-MEX

Atmospheric Environment 43 (2009) 2672–2677 Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv Short communication Tethered balloon-based soundings of ozone, aerosols, and solar radiation near Mexico City during MIRAGE-MEX J.P. Greenberg * , A.B. Guenther, A. Turnipseed National Center for Atmospheric Research, Boulder, CO 80307, USA a r t i c l e i n f o a b s t r a c t Article history: Received 17 December 2008 Received in revised form 6 February 2009 Accepted 8 February 2009 A tethered balloon sampling system was used to measure vertical proﬁles of ozone, particles, and solar radiation in the atmospheric boundary layer on the northern edge of Mexico City, in March 2006 as part of the Megacity Impact on Regional and Global Environment-Mexico experiment. Several commercial sensors, designed for surface applications, were deployed on a tethered balloon platform. Proﬁles indicate that for these 3 scalars the boundary layer (surface up to 700 m) was well mixed in the period 10:00–16:00 LST. Good agreement was observed for median surface and balloon ozone and particle number concentrations. For most proﬁles, the surface deposition of ozone was not signiﬁcant compared to median proﬁle concentrations. Particle number concentration (0.3, 0.5, 1.0 and 5.0 m m) also showed little variation with attitude. Radiatproﬁles showed a monotonic increase in diffuse radiation from the maximum altitude of proﬁles to the surface. Consequently, it was inferred that surface measurements of these likely were representative of lower boundary layer values during this time period. O 2009 Elsevier Ltd. All rights reserved. Keywords: Tethered balloon Boundary layer Megacity Ozone Radiation Particles 1. Introduction The MIRAGE (Megacity Impact on Regional and Global Envi- ronment)-MEX ﬁeld campaign (March 2006) was designed to examine the chemical and physical transformations of gases and aerosols in the polluted outﬂow from Mexico City. The campaign included observations from ground stations, aircraft, and satellites. (An overview of the experiment is given in Molina et al., 2008). Surface measurements were made at three primary sites: central Mexico City (T0, Instituto Mexicano de Petroleo), the Technical University of Tecamac (T1), approximately 35 km NW of T0, and Rancho de Bisnaga (T2), approximately 70 km from T0. The sites were selected to characterize polluted MC air as it aged in transit from its source (arbitrarily set at T0). The balloon–platform proﬁles presented here are from the T1 site (19N42.184, 98W59.917, 2270 m asl) from 13 to 28 March 2006. The primary objective of the tethered balloon study was to deter- mine if surface measurements accurately reﬂected concentrations in the boundary layer, so that ground based data might be extended to characterize to the atmospheric boundary layer analysis. Vertical proﬁles of several variables (ozone, particles, and direct and diffuse * Corresponding author. National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307, USA. Tel.: þ1 303 497 1454; fax: þ1 303 497 1400. E-mail address: greenber@ucar.edu (J.P. Greenberg). 1352-2310/$ – see front matter O 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2009.02.019 solar radiation) were made to illustrate mixing from the surface to the maximum balloon height (usually between 400 and 700 m above ground level). 2. Experiment details 2.1. Instrumentation Extensive details of tethered balloon proﬁling in the atmo- spheric boundary layer have been provided previously (Greenberg et al., 1999; Greenberg and Guenther, 2002). Several commercial lightweight sensors were deployed on the balloon platform. Ozone was measured by a UV absorption ozone analyzer (2B Technologies, Boulder, CO, 2.1 kg); a glass ﬁber ﬁlter was placed on the inlet to prevent interference of dust in the optical cell. Ten second average data are reported for each proﬁle. The relative standard deviation of 1 min averaged data was determined experimentally to be approximately 1.3% at approximately 70 ppb. An optical particle counter (Abacus, Particle Measurement Systems, Boulder, CO, 1 kg) was also deployed. Particles numbers were counted for discrete 0.3, 0.5, 1 and 5 m m sizes; 45 s average number concentrations are reported. The reported collection efﬁciency is approximately 20% for 0.3 m m particles. Total (global), direct (total minus diffuse) and diffuse radiation were measured using Sunshine Sensor, Model BF3 (Delta-T Devices, Ltd., Cambridge, UK, 0.5 kg). This detector has a sensor array which requires no shadow band and need not be