studies using single-value, average-type country-level indicators of time-related trade costs such as the Doing Business Indicators. Instead, we compute a novel measure of import uncertainty taking advantage of the time-varying within-country distribution of Customs clearance times across manufacturing firms sourced from the World Bank Enterprise Surveys (WBES), thereby accounting for the heterogeneity of border times at the country-sector-firm-year level (Volpe Martincus, 2016). Specifically, we consider the within-country-sector-year interquartile range of the days elapsed between the time of arrival of imported inputs at the destination port of entry and the time of release from Customs, for a sample of 48 developing countries over 2006-2014.

Second, by matching this dataset with information on firm export dynamics at the origin-destinationsector-year level obtained from the World Bank’s Exporter Dynamics Database (EDD), we are able to shed light on how uncertainty in the time to import affects the decision of (i) non-exporters to enter foreign markets; (ii) both new and incumbent exporters to exit foreign markets, and (iii) firms to keep on exporting one, two and three years after the date they started serving the foreign market. Therefore, our paper emphasizes the granular origins of aggregate trade performance by exploiting firm-level information to derive country-sector level indicators of export dynamics. Export outcomes at the macro-level are driven by the activities of individual firms operating in different sectors across the country, with sometimes only a handful of them - dubbed export superstars - accounting for the lion’s share of total exports (Freund and Pierola, 2015).

By constructing a new measure of uncertainty in border clearance times for imports, we quantify a new source of trade costs. Traditionally captured by a wide range of variables including standard gravity-type measures such as bilateral distance, tariffs, contiguity, common language and participation in trade agreements, trade costs also relate to a country’s legal and regulatory framework, as well as the availability of quality infrastructure and other trade facilitation measures aimed for instance at reducing administrative red tape. Abundant research highlights the sizeable impact of trade costs on aggregate export volumes,<sup>3</sup> the intensive and extensive margins of trade<sup>4</sup> and export survival<sup>5</sup> on the one hand, and their large growth- and welfare-implications on the other (Anderson and van Wincoop, 2004).<sup>6</sup> Our results suggest that uncertainty in the time required to clear imported inputs at the border impacts neither the entry nor the exit rate of manufacturing firms in developing countries, but translates into lower survival rates for new exporters, with a smaller number of manufacturing firms continuing to serve the foreign market beyond their first year of entry. Interestingly, this effect grows larger over time as input-importing exporters bear the increasing reputational costs associated with missed delivery deadlines, and appears to be driven by South-North trade, possibly reflecting the time-sensitivity of buyers in developed countries. We also find that the export dynamics-effects of import uncertainty are

> 3See for example Limao (2001); Coulibaly and Fontagn ́e (2006); Blonigen and Wilson (2008) and Volpe Martincus, Carballo, and Cusolito (2017).

> 4See for instance Debaere and Mostashari (2010); Shepherd (2010); Dennis and Shepherd (2011); Albornoz, Calvo Pardo, Corcos, and Ornelas (2012); Regolo (2013); Feenstra and Ma (2014) and Beverelli, Neumueller, and Teh (2015).

> 5See for instance Brenton, Saborowski, and von Uexkull (2010); Brenton, Cadot, and Pierola (2012); Fugazza and Molina (2016); Cadot, Iacovone, Pierola, and Rauch (2013); Araujo, Mion, and Ornelas (2016) and Carr`ere and Strauss-Kahn (2017). 6Since the seminal work of Romer and Frankel (1999) who show that trade increases income, the literature has burgeoned with studies aimed at identifying the positive relationship between trade and economic growth. Winters (2004) provides an extensive overview of the literature.

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