diff --git a/corsika/detail/modules/writers/LongitudinalWriter.inl b/corsika/detail/modules/writers/LongitudinalWriter.inl
new file mode 100644
index 0000000000000000000000000000000000000000..f971e8b33e1adfd83b111e5e43b6074321b07a61
--- /dev/null
+++ b/corsika/detail/modules/writers/LongitudinalWriter.inl
@@ -0,0 +1,157 @@
+/*
+ * (c) Copyright 2021 CORSIKA Project, corsika-project@lists.kit.edu
+ *
+ * This software is distributed under the terms of the GNU General Public
+ * Licence version 3 (GPL Version 3). See file LICENSE for a full version of
+ * the license.
+ */
+
+#pragma once
+
+#include <corsika/framework/core/ParticleProperties.hpp>
+#include <corsika/framework/core/PhysicalUnits.hpp>
+#include <corsika/framework/utility/FindXmax.hpp>
+
+#include <corsika/media/ShowerAxis.hpp>
+
+#include <exception>
+
+namespace corsika {
+
+ template <typename TOutput>
+ inline LongitudinalWriter<TOutput>::LongitudinalWriter(ShowerAxis const& axis,
+ GrammageType dX,
+ size_t const nBins)
+ : TOutput(number_profile::ProfileIndexNames)
+ , showerAxis_(axis)
+ , dX_(dX)
+ , nBins_(nBins) {}
+
+ template <typename TOutput>
+ inline void LongitudinalWriter<TOutput>::startOfLibrary(
+ boost::filesystem::path const& directory) {
+ TOutput::startOfLibrary(directory);
+ }
+
+ template <typename TOutput>
+ inline void LongitudinalWriter<TOutput>::startOfShower(unsigned int const showerId) {
+ TOutput::startOfShower(showerId);
+ // reset profile
+ profile_.clear();
+ profile_.resize(nBins_);
+ }
+
+ template <typename TOutput>
+ inline void LongitudinalWriter<TOutput>::endOfLibrary() {
+ TOutput::endOfLibrary();
+ }
+
+ template <typename TOutput>
+ inline void LongitudinalWriter<TOutput>::endOfShower(unsigned int const showerId) {
+
+ int iRow{0};
+ for (number_profile::ProfileData const& row : profile_) {
+ // here: write to underlying writer (e.g. parquet)
+ TOutput::write(showerId, iRow * dX_, row);
+ iRow++;
+ }
+ TOutput::endOfShower(showerId);
+ }
+
+ template <typename TOutput>
+ template <typename TTrack>
+ inline void LongitudinalWriter<TOutput>::write(TTrack const& track, Code const pid,
+ double const weight) {
+ GrammageType const grammageStart = showerAxis_.getProjectedX(track.getPosition(0));
+ GrammageType const grammageEnd = showerAxis_.getProjectedX(track.getPosition(1));
+
+ // Note: particle may go also "upward", thus, grammageEnd<grammageStart
+ int const binStart = std::ceil(grammageStart / dX_);
+ int const binEnd = std::floor(grammageEnd / dX_);
+
+ for (int bin = binStart; bin <= binEnd; ++bin) {
+ if (pid == Code::Photon) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::Photon)] +=
+ weight;
+ } else if (pid == Code::Positron) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::Positron)] +=
+ weight;
+ } else if (pid == Code::Electron) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::Electron)] +=
+ weight;
+ } else if (pid == Code::MuPlus) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::MuPlus)] +=
+ weight;
+ } else if (pid == Code::MuMinus) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::MuMinus)] +=
+ weight;
+ } else if (is_hadron(pid)) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::Hadron)] +=
+ weight;
+ }
+ if (is_charged(pid)) {
+ profile_[bin][static_cast<int>(number_profile::ProfileIndex::Charged)] += weight;
+ }
+ }
+ }
+
+ template <typename TOutput>
+ inline void LongitudinalWriter<TOutput>::write(GrammageType const Xstart,
+ GrammageType const Xend, Code const pid,
+ double const weight) {
+ double const bstart = Xstart / dX_;
+ double const bend = Xend / dX_;
+
+ if (abs(bstart - floor(bstart + 0.5)) > 1e-2 ||
+ abs(bend - floor(bend + 0.5)) > 1e-2 || abs(bend - bstart - 1) > 1e-2) {
+ CORSIKA_LOGGER_ERROR(TOutput::getLogger(),
+ "CONEX and Corsika8 dX grammage binning are not the same! "
+ "Xstart={} Xend={} dX={}",
+ Xstart / 1_g * square(1_cm), Xend / 1_g * square(1_cm),
+ dX_ / 1_g * square(1_cm));
+ throw std::runtime_error(
+ "CONEX and Corsika8 dX grammage binning are not the same!");
+ }
+
+ int const bin = int((bend + bstart) / 2);
+
+ if (pid == Code::Photon) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::Photon)] += weight;
+ } else if (pid == Code::Positron) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::Positron)] +=
+ weight;
+ } else if (pid == Code::Electron) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::Electron)] +=
+ weight;
+ } else if (pid == Code::MuPlus) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::MuPlus)] += weight;
+ } else if (pid == Code::MuMinus) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::MuMinus)] += weight;
+ } else if (is_hadron(pid)) {
+ profile_.at(bin)[static_cast<int>(number_profile::ProfileIndex::Hadron)] += weight;
+ }
+ if (is_charged(pid)) {
+ profile_[bin][static_cast<int>(number_profile::ProfileIndex::Charged)] += weight;
+ }
+ }
+
+ template <typename TOutput>
+ inline YAML::Node LongitudinalWriter<TOutput>::getConfig() const {
+
+ YAML::Node node;
+
+ node["type"] = "LongitudinalProfile";
+ node["units"]["grammage"] = "g/cm^2";
+ node["bin-size"] = dX_ / (1_g / square(1_cm));
+ node["nbins"] = nBins_;
+
+ return node;
+ }
+
+ template <typename TOutput>
+ inline YAML::Node LongitudinalWriter<TOutput>::getSummary() const {
+ YAML::Node summary;
+ return summary;
+ }
+
+} // namespace corsika
diff --git a/corsika/modules/writers/LongitudinalWriter.hpp b/corsika/modules/writers/LongitudinalWriter.hpp
new file mode 100644
index 0000000000000000000000000000000000000000..e1073e64eced5fc5147a16c185d998f1f715db56
--- /dev/null
+++ b/corsika/modules/writers/LongitudinalWriter.hpp
@@ -0,0 +1,140 @@
+/*
+ * (c) Copyright 2021 CORSIKA Project, corsika-project@lists.kit.edu
+ *
+ * This software is distributed under the terms of the GNU General Public
+ * Licence version 3 (GPL Version 3). See file LICENSE for a full version of
+ * the license.
+ */
+
+#pragma once
+
+#include <corsika/output/BaseOutput.hpp>
+#include <corsika/framework/core/ParticleProperties.hpp>
+#include <corsika/framework/core/PhysicalUnits.hpp>
+#include <corsika/media/ShowerAxis.hpp>
+#include <corsika/modules/writers/WriterOff.hpp>
+#include <corsika/modules/writers/LongitudinalProfileWriterParquet.hpp>
+
+#include <vector>
+#include <array>
+
+/**
+ * @file LongitudinalWriter.hpp
+ */
+
+namespace corsika {
+
+ /**
+ * Local helper namespace to store number and names of particle number profile columns.
+ */
+ namespace number_profile {
+
+ /**
+ * Definition of longitudinal profile columns.
+ */
+ enum class ProfileIndex {
+ Charged,
+ Hadron,
+ Photon,
+ Electron,
+ Positron,
+ MuPlus,
+ MuMinus,
+ Entries
+ };
+
+ /**
+ * Number of columns (static).
+ */
+ size_t constexpr NColumns = static_cast<size_t>(ProfileIndex::Entries);
+
+ /**
+ * Names of columns in output.
+ */
+ static std::array<char const*, NColumns> constexpr ProfileIndexNames{
+ {"charged", "hadron", "photon", "electron", "positron", "muplus", "muminus"}};
+
+ /**
+ * Data type to store column data.
+ */
+ typedef std::array<double, NColumns> ProfileData;
+ } // namespace number_profile
+
+ // clang-format-off
+ /**
+ * The LongitudinalWriter can be used to pool the particle counts of several
+ * longitudinal profile processes into one output file/stream.
+ *
+ * Typically several processes/modules can lead to particle counts along the shower axis
+ * in the shower. The LongitudianalWriter can be used in combination with the SubWriter
+ * class to collect all of them into a single output stream:
+ *
+ * \code {.cpp}
+ * # showerAxis must be a ShowerAxis object
+ * # the X binning can be specified.
+ * LongitudinalWriter profile{showerAxis, 10_g / square(1_cm), 200};
+ * # add to OutputManager:
+ * output.add("profile", profile);
+ * # add SubWriters, e.g. LongitudinalProfile, CONEX:
+ * LongitudinalProfile<SubWriter<decltype(profile)>> long{profile};
+ * CONEXhybrid<SubWriter<decltype(profile)>> conex{..., profile};
+ * ...
+ * \endcode
+ *
+ * The default output option is parquet format.
+ *
+ * @tparam TOutput
+ */
+ // clang-format-on
+
+ template <typename TOutput = LongitudinalProfileWriterParquet<number_profile::NColumns>>
+ class LongitudinalWriter : public TOutput {
+
+ public:
+ /**
+ * Construct a new writer.
+ */
+ LongitudinalWriter(ShowerAxis const& axis,
+ GrammageType dX = 10_g / square(1_cm), // profile binning
+ size_t const nBins = 200); // number of bins
+
+ void startOfLibrary(boost::filesystem::path const& directory) final override;
+
+ void startOfShower(unsigned int const showerId) final override;
+
+ void endOfShower(unsigned int const showerId) final override;
+
+ void endOfLibrary() final override;
+
+ /**
+ * Add continuous profile.
+ */
+ template <typename TTrack>
+ void write(TTrack const& track, Code const pid, double const weight);
+
+ /**
+ * Add binned profile.
+ */
+ void write(GrammageType const Xstart, GrammageType const Xend, Code const pid,
+ double const weight);
+
+ /**
+ * Return a summary.
+ */
+ YAML::Node getSummary() const;
+
+ /**
+ * Return the configuration of this output.
+ */
+ YAML::Node getConfig() const;
+
+ private:
+ ShowerAxis const& showerAxis_; ///< conversion between geometry and grammage
+ GrammageType dX_; ///< binning of profile.
+ size_t nBins_; ///< number of profile bins.
+ std::vector<number_profile::ProfileData> profile_; // longitudinal profile
+ };
+
+} // namespace corsika
+
+#include <corsika/detail/modules/writers/LongitudinalWriter.inl>